design and control of compact legged- wheeled robot spicar · developed – term “spicar” is...

pg. i Zeeshan Ansari (s09466807)

BEng (Hons) Electronic Engineering

Faculty of Computing, Engineering and the Built Environment

School of Engineering and Built Environment

Student Number: s09466807

Submission Date:

Supervisor:

Design and control of compact legged-

wheeled robot "Spicar"

May / 2017

Dr Mohamed Kara-Mohamed

pg. ii Zeeshan Ansari (s09466807)

pg. iii Zeeshan Ansari (s09466807)

Acknowledgements

I wish to express my sincere gratitude to Dr Mohamed Kara Mohamed for his

unflinching encouragement, support and guidance during this project. Very special

thanks to Sir Alan Pendry whose lectures and support on “Project Management” led

me to the completion of this project.

Also special thanks to senior demonstrator Mr Chris Evans for his good help

with Legs 3D printing and other hardware assembly. Also would senior demonstrator

Mr Ishver Patel for his valuable help with the technical details and problem solving of

the Spicar robot’s wheels and axles. Special thanks to all classmates, indeed.

I would dearly like to thank my Dear Parents who were always a pillar of support

throughout my education and all my respected tutors especially Sir Jagjit Sehra, Sir

Gurvinder Dubb and Dr Tony Wilcox for all their support throughout this degree. I

would also like to extend my very special thanks to Syeda F.Z and Mr. M Ejaz

Mughal for motivation and moral support.

pg. iv Zeeshan Ansari (s09466807)

Abstract

In the past, robots were usually raised on a fixed platform and locomotion was

not required. But in the last two decades their transition from fixed to mobile robots

has extended their operations to open air spaces and busy hubs like airports,

hospitals, shopping malls, metro stations etc. These are called field and service

robots. Robots that use both legs and wheels for locomotion are called hybrid. A

hybrid robot can switch between different modes of locomotion namely walking with

legs, rolling on wheels and “rolking” which means using wheels and legs

simultaneously.

This project has targeted at creating a hybrid robot possessing a six-legged

walking system and a four-wheeled locomotion system.

Out of many walking machines, hexapod with 12 DOF (degree of

freedom) is chosen to perform legged locomotion as it offers best stability

on uncertain surfaces. Operations include walking forward, backward,

right and left turn.

For rolling locomotion, four wheels are added under the chassis. This

locomotion would perform forward and backward rolling.

This project has developed a generalised legged-wheeled robotic platform that

can manually be switched between legs’ and wheels’ mode. It fully demonstrates

walling and rolling locomotion.

In future this platform can be modified and programmed to an autonomous

robot to perform increasingly complex motions and functions. Typical applications

include Search & Rescue, reconnaissance, extra-terrestrial explorations etc.

pg. 1 Zeeshan Ansari (s09466807)

Table of Contents

1 Introduction ........................................................................................................ 6

1.1 Scope of the project ...................................................................................... 6

1.2 Rationale ....................................................................................................... 7

1.3 Motivation ...................................................................................................... 8

1.4 Aim and objectives ........................................................................................ 8

2 Review of existing knowledge ........................................................................ 10

2.1 Background ................................................................................................. 10

2.2 Locomotion systems ................................................................................... 13

2.2.1 Walking locomotion: ............................................................................. 14

2.2.2 Rolling locomotion: ............................................................................... 14

2.2.3 Hybrid locomotion: ............................................................................... 15

3 Project Specification ........................................................................................ 16

3.1 Non-functional Requirements ...................................................................... 16

3.1.1 Product Requirements ......................................................................... 16

3.1.2 Organisational Requirements............................................................... 16

3.1.3 External Requirements ........................................................................ 17

3.2 Functional Requirements ............................................................................ 17

3.2.1 Category 1 ........................................................................................... 17

3.2.2 Category 2 ........................................................................................... 17

4 Design Considerations .................................................................................... 18

4.1 Gait planning ............................................................................................... 19

4.2 Spicar Robot Control ................................................................................... 19

4.3 Spicar Design Flowchart ............................................................................. 21

5 Hardware and Software ................................................................................... 23

5.1 Hardware .................................................................................................... 23

5.1.1 Robot Chassis ...................................................................................... 23


5.1.2 Micro-controller .................................................................................... 27

5.1.3 Servos .................................................................................................. 30

5.1.4 DC motors ............................................................................................ 34

5.1.5 Power Source ...................................................................................... 35

5.2 Software ...................................................................................................... 38

6 Methodology ..................................................................................................... 39

6.1 Software and Spiral methodologies............................................................. 39

6.2 Waterfall ...................................................................................................... 39

6.3 Chosen methodology .................................................................................. 40

6.3.1 Methodology Flowchart ........................................................................ 41

7 Project Planning – Gantt chart ........................................................................ 43

7.1 Main milestones of the project .................................................................... 43

7.2 Deliverables of the project ........................................................................... 44

7.3 Safety Assessment ..................................................................................... 45

7.4 Ethical Considerations ................................................................................ 45

8 Spicar Control .................................................................................................. 46

8.1 PWM Signal Generation .............................................................................. 46

8.2 Controlling the Servos and DC motors ........................................................ 46

8.3 Spicar Open-Loop Control .......................................................................... 48

8.3.1 Programme Flow chart ......................................................................... 48

8.4 Dagu Spider Robot controller ...................................................................... 49

9 Hardware Implementation ............................................................................... 50

9.1 Design and Assembly ................................................................................. 50

9.1.1 Legs design.......................................................................................... 51

9.1.2 Spicar Assembly .................................................................................. 56

9.2 Hardware Block Diagram ............................................................................ 57

10 Software Implementation ............................................................................. 58


10.1 Walking Locomotion .................................................................................... 58

10.1.1 Inverse and Forward kinematics .......................................................... 58

10.1.2 Spicar Gaits ......................................................................................... 59

10.1.3 Analysis of the Walking Gaits............................................................... 60

10.1.4 Tripod, the Chosen Gait Implementation ............................................. 61

10.2 Rolling Locomotion...................................................................................... 69

11 Testing, Results and Evaluation ................................................................. 72

11.1 Unit Testing ................................................................................................. 72

11.2 Function Testing.......................................................................................... 72

11.3 Evaluation ................................................................................................... 73

11.3.1 Final Functionality ................................................................................ 73

12 Discussion and Conclusion ......................................................................... 74

13 Future Work .................................................................................................. 76

13.1 Autonomous Control ................................................................................... 76

13.1.1 Sensor Configuration ........................................................................... 77

14 References .................................................................................................... 82

15 Bibliography .................................................................................................. 85

16 Appendix A – Walking Locomotion Code ................................................... 86

17 APPENDIX B – Rolling Locomotion Code .................................................. 98

18 APPENDIX C – Hardware Components and Prices .................................. 101

19 APPENDIX D – Project Proposal ............................................................... 102

20 APPENDIX E – Future Work Further Research ........................................ 103

20.1 Sensor Implementation Code: ................................................................... 103

20.2 Research for Further Useful Improvements .............................................. 107


List of Figures

Figure 1 Old Spider Robot Projects ........................................................................... 11

Figure 2 Pros and Cons ............................................................................................ 13

Figure 3 Scheme for preliminary layout design of Spicar .......................................... 18

Figure 5 Legs Description & Gates (Tedeschi and Carbone, 2014) .......................... 19

Figure 6 Hierarichal control architecture for Spicar ................................................... 20

Figure 7 Spicar Design Flowchart (Tedeschi and Carbone, 2014) ............................ 22

Figure 8 mBot-Blue Educational Programmable Robot (Bluetooth Version)

(Robotshop.com, 2017) ...................................................................................... 23

Figure 9 LEGO® MINDSTORMS® EV3 (EU Version) (Robotshop.com, 2017) ........ 24

Figure 10 Lynxmotion AH2 Hexapod Robot Kit (BotBoarduino) (Robotshop.com,

2017) .................................................................................................................. 25

Figure 11 DIY Six Feet Robot 6-Legged 6DOF Hexapod4 Spider Robot with Servo

(banggood.com, 2017) ....................................................................................... 26

Figure 12 The Axon II (Societyofrobots.com, 2017) .................................................. 28

Figure 13 Dagu Spider Robot Controller (cdn.sparkfun.com, 2017) .......................... 29

Figure 14 Tower Pro Micro Servo 9g (micropik.com, 2017) ...................................... 30

Figure 15 Servo Motor Block Diagram (Robotplatform.com, 2017) ........................... 31

Figure 16 PWM Process (Daware, 2017). ................................................................. 32

Figure 17 DC Motor (Pololu.com, 2017) .................................................................... 35

Figure 18 NiMH battery structure (Skylightupower.com, 2017) ................................. 35

Figure 19 LiPo battery structure (Skylightupower.com, 2017) ................................... 36

Figure 20 (LiPo) 7.4 V 450 mAh 40 C Conrad energy Stick (produktinfo.conrad.com,

2017) .................................................................................................................. 37

Figure 21 Waterfall Method (Bowes, 2017) ............................................................... 40

Figure 22 Methodology Flowchart ............................................................................. 42

Figure 23 Project Gantt chart .................................................................................... 44

Figure 24 Servo's High Pulse Width determines the Angle Position (Johns, 2017) ... 47

Figure 25 Program Flow chart ................................................................................... 49

Figure 26 Robot parts ................................................................................................ 50

Figure 27 Robot ......................................................................................................... 50

Figure 28 Leg (TIBIA design in Thomas, 2014)

Figure 29 Tibia drawing and 3D print ........................................................................ 52

Figure 30 Leg Brackets ............................................................................................. 53


Figure 31 Femur and “Femur Support” ...................................................................... 54

Figure 32 Spicar Base Measurements ...................................................................... 55

Figure 33 Brackets, Wheels / Axle fitting for rolling locomotion ................................. 56

Figure 34 System Integration .................................................................................... 56

Figure 35 Hardware Block Diagram .......................................................................... 57

Figure 36 Wave Gait (Do, 2017). ............................................................................... 59

Figure 37 Tripod Gait (Do, 2017). .............................................................................. 60

Figure 38 Gait Selections (Pairs), (Liang, 2017) ........................................................ 61

Figure 39 Common (Tripod) Gait and Stepping Sequence (McComb, 2017) ............ 62

Figure 40 Legs’ Servos attached to Pins on Microcontroller ..................................... 64

Figure 41 Top View of Spicar .................................................................................... 65

Figure 42 Legs in loop motion ................................................................................... 65

Figure 43 Leg Motion ................................................................................................ 66

Figure 44 Loop of leg1 & leg4 when walking towards right ....................................... 67

Figure 45 Movement of each leg in their loop for Rightwards’ Walking ..................... 68

Figure 46 Forward Logic (APPENDIX B – Rolling Locomotion Code) ....................... 69

Figure 47 Backward Logic (APPENDIX B – Rolling Locomotion Code) .................... 70

Figure 48 Right Turn Logic (APPENDIX B – Rolling Locomotion Code) ................... 71

Figure 49 Left Turn Logic (APPENDIX B – Rolling Locomotion Code) ...................... 71

Figure 50 Autonomous Spicar Closed Loop Feedback Control ................................. 77

Figure 51 Devantech SRF08 UltraSonic Ranger (coecsl.ece.illinois.edu, 2017) ....... 78

Figure 52 Using the I2C Bus, SCL & SDA (Robot-electronics.co.uk, 2017) .............. 80

Figure 53 Start and Stop Sequences (Robot-electronics.co.uk, 2017) ...................... 80

Figure 54 Data Transfer (Robot-electronics.co.uk, 2017) .......................................... 81


1 Introduction

A robot can be defined as a machine designed to perform one or more tasks

automatically through interaction with its own brain (called a controller) and the

outside world. Increasing trend of developing autonomous mobile robots is replacing

humans in some of their activities. This is true especially in situations where human

lives are endangered due to the amount of risks attached to them, or because of

significant personal or industrial requirements where human operators should

perform tasks. Therefore, there is a high demand of developing highly robust and

multi-functional robots for different tasks, situations and missions (Jakimovski et al.,

2017).

In this work, design and control of compact legged-wheeled robot “Spicar” is

developed – Term “Spicar” is coined from Spider and car; as it is a hexapod spider

robot to walk with additional features of wheels where it drives like a toy car. “Spi”

and “car” makes the word “Spicar”. Legged and wheeled robots use two different

mechanisms for their operations. Usually, legged robots are slow that make them

more applicable for uncertain territories where wheeled robots are unsuitable. On the

other hand wheeled robots provide best mobility on both even or hard surfaces

because of rolling locomotion, locomotion is the physical ability to move from one

place to another.

An important characteristic that has been introduced within this hybrid robot is

that it is capable of executing both walking and rolling locomotion. Also kinematic

analysis is used to develop the most stable gait for walking the robot and finding out

the location of the robot in the world coordinate frame for mapping and driving it. For

rolling locomotion Proportional Control Strategy is developed for forward and

backward rolling. Product (autonomous hybrid robot) would have many robotic

applications such as Search & Rescue, reconnaissance, extra-terrestrial exploration

etc.

1.1 Scope of the project

Hybrid robots are gaining great amount of recognition due to the characteristics

they offer and their better performance and efficiency over different terrains. This

project has primarily aimed at more generalised legged-wheeled robotic platform that

can manually be switched between legs’ and wheels’ mode. Finally, walking and

rolling locomotion can be modified with sensors and control strategy to an


autonomous robot that can demonstrate the combined capability of legs and wheels

with respect to terrain types they operate on. It will automatically switch between

legs’ mode for smooth stroll on even surfaces and wheels’ mode to maximise the

speed on approaching uneven surfaces.

1.2 Rationale

Robots are taking over humans in some of the activities where human life is

endangered or in situations/missions where human operators have become

unavailable to perform tasks. Physical ability to move from one place to another

(locomotion) defines the core operation of robots. Locomotion in even and uneven

terrains is important for wide range of robotic applications including Search& Rescue

operations and extra-terrestrial exploration etc. A robot that can roll over even

terrains to maximise the speed and walk on uneven terrains to surmount obstacles

must be operated by rolling and walking locomotion.

One of the fundamental problems of mobile robotics is locomotion. Three

primary types of locomotion include legged, wheeled and articulated bodies. Factors

that normally effect locomotion are environment, stability, systems complexity and the

cost. Keeping in mind the higher indices of stability, efficiency and increased payload

rolling locomotion is employed in the first place. However rolling locomotion still

prevents its efficient operation on unstructured environments. Despite the significant

effort to overcome the problem of smooth rolling over unstructured terrains wheels

are still far from being perfect for locomotion in all types of environments

(Saudabayev et al., 2017).

Inspired from the nature, walking locomotion offers robust mechanism to tackle

the difficulties of rough terrains. Legs ability of efficient navigation on even terrains

alongside uneven terrains in walking locomotion could have claimed to be a universal

solution for mobile robot locomotion. However, static and dynamic stability is still one

of the major challenges for legged systems. Hybrid robots have emerged offering

combined capabilities of rolling and walking locomotion. With hybrid locomotion, a

robot would be able to maximise the speed on even terrains using wheels and step

over obstacles on uneven terrains using walking locomotion (Saudabayev et al.,

2017).


1.3 Motivation

Motivation behind undertaking this project was the development of knowledge

and skills that this project offers for a graduate electronics engineer. Required

knowledge and skills for this project include programming skills, electronics circuit

design, mechanical design, simulation software, mathematical modelling, control

strategy and dynamic knowledge.

Author wanted to get together, all the knowledge and skills gained previously, in

one place to implement using a new platform and develop something that can be

called innovative, while further polishing his skills to a higher level and gaining in-

depth theoretical knowledge. As most of the major modules studied in previous years

are pre-requisites for this project which was also a major reason to choose this

project.

To summarise, this project in its entirety will demonstrate 80% of the knowledge

and skills acquired and yet-to-be acquired until the end of the graduate degree; it is a

massive step into the world of robotics; hardware, locomotion systems and control

strategies. Although it’s a challenging project but hard work and dedication would

provide good practice for prospective electronics engineer.

1.4 Aim and objectives

Aim is to design and control an autonomous robot with compact legged/wheeled

capabilities to maximise the speed of the robot. Robot must have the capacity to

perform two functions; it will switch to wheels’ mode on even surfaces to amplify the

speed and manual/automatic change to legs mode for smooth stroll on drawing

closer to uneven surfaces.

After a research and literature review has been carried out, the following

objectives shall be achieved:

Determine suitable hardware for robot structure; i.e. Microcontroller, legs,

wheels, sensors and so forth.

Mechanical design of legs, wheels and sensors to further assemble the

components into a robot.

Electronic circuit design and configuration of wheels, legs and sensors to

aid performance.

Develop block diagram of system hardware to write program for system

and algorithm(s) (high-level description) of the system software.


Derive equations to obtain mathematical model of robot.

Program the microcontroller to implement a suitable control strategy.

Basically implementing manual switch between legged and wheeled

modes.

Finally adding sensors to switch it to autonomous control between two

modes (Optional Objective).

Develop appropriate test plans for circuit simulation and to check the

functionality of the control strategy and robot as a whole.

Evaluate final product as an autonomous robot (Optional Objective).


2 Review of existing knowledge

2.1 Background

Robotics is a field of science that develops robots which have hardware and a

software side. Robotics is a technology that amalgamates computer, electronics,

electrical and mechanical engineering. It involves a broad spectrum of activities like

design, construction, application and various operations of robots. It also involves

designing computer systems for sensory feedback, information processing and

control.

This idea of developing machines that can operate independently was present

as early as the classical times and efforts were being made to improve such

machines. But it was not until the twentieth century that research into the potential

uses and functions of robots gained momentum. Scientists have been increasingly

interested in artificial intelligence (AI) as well which is the technology that is trying to

make robots think like humans and make logical decisions when provided with a

difficult situation. Behind it is the thought that robots will one day have the ability to

copy human behaviour and look much like a human in outward appearance. This is

the most inspiring field of robotics today.

Robots are machines that have vast applications in practical life. They can be

used for services in dangerous situations or an emergency that calls for quick action

where situation is life threatening for humans e.g. in diffusing bombs, work in mines,

space exploration, deep sea research for history or search for something like

shipwreck etc. They have numerous applications in assembly lines in factories and

assist in packaging, labelling etc. They reduce the cost of production while increasing

efficiency for the business. Bio-tech or bio-engineering also employs robots. Some

robots are designed from inspiration from nature and life around us, so they are

called bio-inspired robots.

Robotics is fast growing in research and applications. It is being adapted as the

technology of the future. They are being built today for use in commercial

applications, as a household aid, space exploration and military uses.

In the 1950’s, movement of a spider robot was controlled manually by an

operator. The motion of early robots was fed into their system beforehand by

scientists and their applications on the ground were not possible.

These are the earliest researches carried out on spider robots in history:-


University of Rome’s hexapod.

MASHA hexapod.

OSU hexapod.

ODEX I hexapod.

ASV hexapod.

Figure 1 Old Spider Robot Projects

In 1972, University of Rome developed the first hexapod robot that worked. It

was a walking machine with electric drives that was controlled by a computer. The

Russian Academy of Sciences in the mid 70’s in Moscow developed a six-legged

walking robot applying a mathematical model of motion control. Masha hexapod

walking robot was the name of the robot developed in 1976 at Moscow State


University (Figure 1b). Masha was able to overcome obstacles using contact on the

feet and a proximity sensor. Then came the “OSU Hexapod” that was developed by

Ohio State University in 1977, OSU could cover short distances and cross hurdles in

the process. It was a success. ODEX I was the first commercially prepared walking

robot developed in 1983. Then came the Adaptive Suspension Vehicle (ASV) in 1986

by the United States. It was a walking vehicle that was large in size and driven by a

human rider. How the robots operate depends on the locomotion system they use,

some important locomotions are discussed below:

In the past, robots were usually raised on a fixed platform and locomotion was

not required. They were used mostly in factories to assist in the assembly lines. But

the last two decades have seen their transition from fixed to mobile robots. Their area

of work extends to open air spaces and busy hubs like airports, hospitals, shopping

malls, metro stations etc. These are called field and service robots. Electric motors

are installed at the joints for mobility. These motors use their maximum torque ability

for robot locomotion and sometimes reach the saturation point especially under

conditions where critical mass and power constraints put limitations on the actuator’s

size. Algorithms for robot motion optimization are used for locomotion with maximum

saturation margin.

Robots that use both legs and wheels for locomotion are called hybrid. A hybrid

robot can switch between different modes of locomotion namely walking with legs,

rolling on wheels and “rolking” which means using wheels and legs simultaneously.

Now the ground on which the robot moves is of different types. It can be smooth,

hilly, slope, muddy, filled with ice, slippery or mushy. A hybrid robot chooses its

locomotion mode after judging the type of terrain through its sensors. This system of

automatic locomotion mode control through sensors runs on measuring and judging

the various characteristics of the ground when the vehicle interacts with it. These

characteristics include slipping and drawbar force of wheel, energy usage and

various terrain parameters. This project is about creating a hybrid robot possessing a

six-legged walking system and a four-wheeled locomotion system. Also kinematic

analysis is used to develop the most stable gait for walking the robot and finding out

the location of the robot in the world coordinate frame for mapping and driving it. For

rolling locomotion Proportional Control Strategy is developed for forward and

backward rolling. Pros and Cons of Wheeled and Legged Robots are given below in

the figure 2.


Figure 2 Pros and Cons

2.2 Locomotion systems

The word locomotion means the act or power of moving from place to place.

The capability of locomotion is a natural feature of humans and animals. Without the

capabilities of locomotion everyday life becomes complicated and tasteless.

Handicapped people have long been taken into account to develop locomotion

systems.

Locomotion system drives the vehicle, decides its mode if provided i.e. compact

legged/wheeled mode, and reaches its goals when executed to perform a certain

task. A good locomotion is critical to the successful operations of a robot. Generally a

robot should be able to perceive the surface (terrain), plan the path, navigate and

obviously avoid the obstacles to reach its destination.

Requirements are to be taken into account in the design process of a

locomotion system for a robot. The main factor is the environment where the robot

needs to operate. Typical design factors include speed, stability, mode switch


between surfaces based on i.e. sensor system and overall control. Locomotion on

even/uneven surfaces can be realised using the principles of rolling, walking,

running, crawling, jumping or wriggling. This project focuses on rolling for even

surfaces and walking/running for uneven surfaces (Leppänen, 2017).

Basically the locomotion system involves the conversion of some source of

energy i.e. electricity, air pressure, noise, sunshine, nuclear power etc. into a

mechanical action that moves a vehicle (a robot). Variety of techniques can be used

to achieve motion. Most common source of energy used is electricity or a battery

power that operates an electric motor.

This robot will also consume battery power for its operation. Direction of the

motors can be changed to achieve forward or backward motion. Similarly motors can

be fed less or more power to slow down or maximise the speed of the robot. Different

kinds of control strategies can also be implemented for variety of robot movement’s

e.g. dancing, turning etc. This project aims to achieve walking and rolling locomotion

which can be further combined to achieve hybrid locomotion.

2.2.1 Walking locomotion:

Walking locomotion is most suitable for uneven surfaces, especially in soft

grounds or grounds with obstacles where wheels locomotion becomes almost

impossible. Legs can be used to provide better mobility when robot approaches

uneven surfaces, they can step over obstacles and move up and down the stairs.

Again the legs’ mode mobility will also depend on the size, type, structure of legs and

the motors driving them as well as the structure of the main robot body. Flexibility can

be introduced in robots body to maximise the motion of legs, while maintaining

stability and to improve its ability to surmount obstacles. The realisation of legged

locomotion is normally based on two mechanisms which are slide and level.

2.2.2 Rolling locomotion:

Wheels locomotion is one of the most common methods of locomotion. Wheels

provide best mobility on even or hard surfaces depending on its structure, type, size,

surface, type of motor driving them and other factors. The wheels can also carry

more load in comparison to walking or other locomotion systems. Two-wheel robot is

sometimes hard to balance. Four and six wheeled robot is a better option for this

project.


2.2.3 Hybrid locomotion:

In hybrid locomotion; wheeled and legged locomotion can be combined as

hybrids to obtain maximum mobility for greatly varying ground conditions. Hybrid

locomotion can guarantee a high speed on wheels and good negotiating capabilities

of legged locomotion (Leppänen, 2017). Locomotion is performed by wheels while

adapting to slow terrain’s changes to legs. In other words on approaching obstacles

bigger than the wheels size or when obstacles prevent driving the robot switches to

walking locomotion. The idea is to make best use of both the locomotion capabilities

for greater mobility.


3 Project Specification

3.1 Non-functional Requirements

3.1.1 Product Requirements

3.1.2 Organisational Requirements


3.1.3 External Requirements

3.2 Functional Requirements

3.2.1 Category 1

The application is intended to control motion of legged-wheeled robot “Spicar”.

3.2.2 Category 2

Following requirements should be not met under given priorities:


4 Design Considerations

It’s not easy to design a hybrid robot “Spicar”. Design of Spicar involves

decisions to be made about the features depending on the technicalities and

operations required. Following are some of the design constraints of Spicar:-

The mechanical structure of the Spicar body

Leg architecture

Wheel and Bracket design

Actuators and drive mechanisms

Control architecture

Power supply

Walking gaits and rolling locomotion

Autonomy

Operation features

Cost

Sensors (Obstacle avoidance capability - (it is secondary objective))

These design issues can be categorized as design inputs (or key features) and

design outputs (or main design characteristics) as illustrated below in figure 3.

Spicar can be designed in various configurations and every design has its own

specifications, criteria, benefits and drawbacks. Each robot design is unique.

Design Inputs Design Outputs

Key Features Main Design Characteristics

Walking gaits and rolling

locomotion

Autonomy

Operation features

Cost

Obstacle avoidance

capability

Preliminary

Layout

Design

Mechanical structure

Legs architecture

Actuators and drive

mechanism

Control architecture

Power supply

Figure 3 Scheme for preliminary layout design of Spicar


4.1 Gait planning

A gait is a defined as the sequence of leg motions which is coordinated with a

sequence of body motions of the robot to move the robot in the required direction and

to change its place. When similar states of the same leg occur at the same interval of

time for all legs during sequential strokes, then these gaits are called periodic gaits.

They are suitable to use over smooth territory. In Figure 5 below, the scheme of

some periodical hexapodal gaits are exhibited. In these diagrams, white colour

shows that the foot of the robot is in contact with ground while the black colour shows

that it’s off ground.

Figure 4 Legs Description & Gates (Tedeschi and Carbone, 2014)

Figure 5(a) shows the robot’s legs description. Figure 5(b) shows the

mechatronic gait which the robot adopts when its speed is slow. When it starts

moving, it starts with its rear-most leg and then all the rest of the legs are moved

forward in sequence. Same gait is repeated on the other side’s set of legs. The

posture of the hexapod remains stable because only one leg is raised at a time while

the other five are grounded.

Figure 5(c) shows the ripple gait which is used for medium speed. Figure 5(d)

shows tripod gait which is a regular periodic gait in which the front and back legs on

one side raise with the contralateral middle leg within the time frame thus forming

alternating tripods. This gait is most appropriate for walking in high speeds over

smooth ground.

4.2 Spicar Robot Control

In figure 6 given below, the control system of this robot is a hierarchical system.


It consists of a host computer, a controller and required actuators and sensors. The

user of the Spicar robot will provide the input for the gait generation for trajectory

which is walking and rolling locomotion in Spicar. This input determines the required

position for legs to conduct walking locomotion and proportional control calculation

for forward or backward rolling locomotion. The trajectory generator sends leg

coordinates to forward kinematic model for each leg. The forward kinematic model

then calculates the leg coordinates into angular coordinates for all the joints. The joint

angles will then enter the control loop. The control at the joint is executed by a PID

open-loop control.

Figure 5 Hierarichal control architecture for Spicar


4.3 Spicar Design Flowchart

The flowchart given below describes the flow of design process.


Figure 6 Spicar Design Flowchart (Tedeschi and Carbone, 2014)


5 Hardware and Software

In-depth research has been conducted on hardware and software requirements

for this project. Hardware options considered were wheeled and legged; humanoid,

quadruped and hexapod robots. Microcontrollers included Dagu spider robot

controller with ATmega2560 processor and The Axon II with ATmega640 processor.

Hardware section also includes detail about Servos, DC motors and Power Source.

Software options involved any software that’s compatible for C/C++ programming.

Hardware and software is justified below:

5.1 Hardware

Hardware part discusses different options for hardware and justifies the most

appropriate ones for this project. Hardware Parts covered here are Robot chassis,

Micro-controllers, Servos, DC Motors and Power Source.

5.1.1 Robot Chassis

Three different robot chassis that were analysed to a great extent for this project

are given below:

5.1.1.1 Wheeled-robots

Re-visiting, aim is to design and control an autonomous robot with compact

legged/wheeled capabilities to maximise the speed of the robot. Keeping aim in mind,

wheeled robots have been researched and studied in detail but results revealed that

their hardware is very hard to be modified to include legs and to further build it to

meet the aim of this project.

Figure 7 mBot-Blue Educational Programmable Robot (Bluetooth Version)

(Robotshop.com, 2017)


The first model is a wheeled-robot called mBot (shown above), mBot comes

with electronics based on arduino open source platform; a blue tooth version for

wireless connections can be used for projects like wall avoidance, line following,

games with other mBots etc. The major disadvantage is that mbot does not offer

enough room to add legs to it, adding legs seems very hard on this robot.

5.1.1.2 Humanoid (Legged-robots)

Humanoid (legged) robot kits like “Mindstorm” (given below in figure 9) were

considered but detailed study on these found out that it is not very suitable for a robot

that needs to switch between wheeled and legged locomotion on approaching even

and uneven surfaces. Adding wheels to humanoid robot is of course possible but as

robot needs switching between two modes its stability on wheels while maximising its

speed becomes a big challenge for a graduate project. Humanoid robots are not

even a good economical option as they are more expensive than the Spider robots.

Figure 8 LEGO® MINDSTORMS® EV3 (EU Version) (Robotshop.com, 2017)

Second model under research was humanoid robot “LEGO® MINDSTORMS® EV3

(EU Version)”. This robot is a comprehensive robotics construction kit with powerful

ARM9 processor. It comes with a programmable brick with an intuitive user interface

and sound, 3 interactive servo motors to move the robot in multiple directions, and it

also includes infrared, touch and colour sensors and everything to build a different

but more humanoid-like robot (Robotshop.com, 2017)


Mindstorms EV3 could have been used to perform excellent walking locomotion

but its biggest drawback is that adding wheels to it restricts the speed to almost zero

because its structure is such that it compromises on its dynamic stability.

5.1.1.3 Spider (Legged-robots)

Spider (legged) robots were found to be the best for this project. Quadruped

and Hexapod can be first programmed to walk/crawl and then two wheels can be

added for wheeled locomotion. Hardware of Spider robots give enough space to add

and fix two big wheels to it. Spider robot is small and has no problem of dynamic

stability (while in operation) as long as the control strategy is well implemented.

Considering its small body and legs’ movements (degree of freedom) and overall

control makes two wheeled locomotion possible and efficient. Hexapod robot can be

best designed, modified, controlled and implemented to meet the aims and objectives

of this project.

5.1.1.3.1 Lynxmotion AH2 Hexapod Robot

Keeping aims and objectives in mind, variety of hexapod and quadruped robots

were then searched in robust depth and consequently the third model considered

was Lynxmotion AH2 hexapod robot kit as shown below in figure 10.

Figure 9 Lynxmotion AH2 Hexapod Robot Kit (BotBoarduino)


Lynxmotion AH2 Hexapod Robot kit comes with advanced mechanical

advantage leg design with 2DOF (degree of freedom), supports forward, reverse,


gradual and in place turning. It also includes BotBoarduino microcontroller and SSC-

32 servo controller. The robot uses 12 HS-422 servos for legs (Robotshop.com,

2016). This kit includes everything to build the robot except the wheels which can be

bought or requested to be made from BCU’s Mechanical Workshop. Price is £393.61,

on top buying wheels and sensors add up to £450, which is not an economical

option.

5.1.1.3.2 DIY Six Feet Robot 6-Legged 6DOF Hexapod4 Spider Robot

with Servo

Similar robot in hardware/software specification was then searched for cheaper

price. One of the best resembling option found out to be “DIY Six Feet Robot 6-

Legged 6DOF Hexapod4 Spider Robot with Servo” and it is shown below in figure

11.

Figure 10 DIY Six Feet Robot 6-Legged 6DOF Hexapod4 Spider Robot with

Servo (banggood.com, 2017)

This hexapod robot comes with even more options i.e. 6DOF (Degree of

freedom) instead of 2DOF in Lynxmotion AH2 Hexapod Robot; it offers flexible

control, more movements and joy. It is light weight and comes with servos but circuit

plate and its battery needs to be installed. Size is about 24(L)*18(W)*12(H) cm

(banggood.com, 2017). Pack at a price of £47.94 includes 1*Hexapod Robot Frame

and 12*9g Servos. One drawback is that it does not include microcontroller which

can be bought separately. This robot has been chosen as the final option based on


its hardware structure, features and price. Then further research for microcontrollers

made the author to decide the best economical microcontroller especially designed

for spider robots.

5.1.2 Micro-controller

Two micro-controllers Axon 2 and Dagu spider robot controller were mainly

compared based on their processors and other features i.e. FLASH, SRAM,

EEPROM, USB interface, I/O pins, number of servos support, analogue inputs,

PWM, serial communication, external interrupt pins and boot-loader etc.

5.1.2.1 Axon II

Axon II micro-controller (shown below in figure 12) has been developed for

robotics hobbyists including beginners and experts. It comes with many great

features for different operations of robots. It uses the powerful ATmega640 as its

processor. A number of important features are given below:

58 I/O Total

16 ADC

25+ Servos

I2C, SPI

3 UART + USB

Up to 8 external interrupts

15 PWM Channels

64KB Flash, 4KB EEPROM, 8KB SRAM

16 MIPS throughput at 16 MHz

6 Timers (four 16-bit, two 8-bit)

pre-programmed with a bootloader - no programmer required

numerical LED display

built in 3.3V, 5V, and unregulated power buses

external memory support (port A)

all software is free

100% open source, large support community

Windows, Mac, and Linux compatible


(Societyofrobots.com, 2016)

Figure 11 The Axon II (Societyofrobots.com, 2017)

5.1.2.2 Dagu Spider Robot controller

Chosen microcontroller; Dagu spider robot controller (shown below in figure 13)

priced at £35.30 is shown below in figure 3.6. It is an Arduino compatible robot

controller designed specifically for robots that uses a large number of servos such as

humanoids, hexapods and serpents. Dagu uses a very powerful ATmega1280 as its

processor with 128K FLASH, 8K SRAM and 4K EEPROM, its drives are up to 48

servos, it has 3A, 5V switch mode power supply and input voltage is from 7V TO

30V. Detailed features are given below:

70 I/O pins terminated with a servo compatible 3 pin male header and a

female header

USB interface and ISP socket

Power switch and reset button

Pin spacing allows custom shields to be made using standard prototype

PCB's

Comes with Arduino bootloader installed

16x 10 bit analogue inputs

Up to 15x PWM outputs (depends on the number of servos in use)


4x serial ports (1 used by USB interface)

1x I²C interface

Can drive up to 48 servos using the Arduino servo library


Figure 12 Dagu Spider Robot Controller (cdn.sparkfun.com, 2017)

The Dagu controller has twice the processing power of the axon 2, and its other

features have almost twice the capability of those of the axon two. Dagu is way more

powerful than axon 2, its powerful features will especially aid in walking and rolling

locomotion and other control strategies.

The reason for selecting this controller is its powerful features (given above)

that allow optimum operations and excellent control of a robot with maximum servos.

Data sheets can be used later on for detailed implementation. Once walking and

rolling locomotion is achieved, sensors can then be researched in detail to modify the

robot to an autonomous compact legged-wheeled robot. Sensor selection is left to

the end of the project.


5.1.3 Servos

Servo motor is a motor which is designed according to specifications for use in

making robots and other control applications. Servo motor is used at high torque for

locating position and controlling speed. Either AC or DC motor is controlled by

servomechanism. So the two major types of servo motors are called AC servo motor

and DC servo motor. The power of servo motor ranges from a fraction of a watt to a

few 100 watts. The rotor of the servo motor is long lengthwise but its diameter is

small. That way its inertia is kept low (Circuitdigest.com, 2017).

The servo motor that this Spicar used is Tower Pro SG90 Micro Servo which is

shown below in figure 14. This servo is a good choice for people who are new in

building electrical gadgets and devices and want to use a motor controller which is

compact in size yet comes with full functionality as it is fitted with gears and feedback

mechanism based on sensors.

Although the SG90 servo is small in size and doesn't weigh much still its motor

generates high power to produce the desired output. Its weight is 9g and the

dimensions are about 22.2 x 11.8 x 31 mm. The voltage needed to operate it is about

5V (4.8V to be exact). The operating speed is 0.1s/60 degree with a stall torque of

1.8kgf.cm. The range of temperature while operating is 0 - 55 degree centigrade and

dead bandwidth is 10 microseconds. This servo motor is available with its 3 horns

and the related hardware for feedback and gearbox (micropik.com, 2017).

Figure 13 Tower Pro Micro Servo 9g (micropik.com, 2017)


5.1.3.1 Servomechanism

In a simple servo motor, only position is controlled but mostly these days servo

motors are used to control both position and speed. The mechanism of servo is a

closed loop system which comprises of a controlled device along with a controller,

output sensor and feedback system. In this project open loop control is used because

sensors are still not implemented which are left for future work discussed in the

section at the end. Following is the block diagram of a servo motor and the logical

servo circuit. It shows what is a servo made up of and how it works (Daware, 2017).

Figure 14 Servo Motor Block Diagram (Robotplatform.com, 2017)

The various parts that make up a servomechanism are discussed below:

(Robotplatform.com, 2017)

(Daware, 2017)

1) Power supply: Just like all electric devices, a servo needs power to operate.

Usually the voltage ranges from 4.8V to 6V but some servos are designed to operate

at lower than 4.8V and higher than 6V. Servos that use more than 6V to operate are

called heavy duty servos. Maximum voltage of a particular servo is written on its

datasheet and it should not be exceeded otherwise the motor will burn.

2) Signal line: A servo has three wires fitted with it. These are a ground wire, a

positive wire and a control wire/line. Two of these wires i.e. positive wire and


negative wire will be used for power supply while the control wire will be used for

sending signals. Signal line is also called the control line of a servo motor because it

sends a pulse with a code which makes the shaft move at a certain angle according

to the code. The pulse has a voltage range of 3V to 5V and this gives a signal to the

shaft. This process is called “Pulse Width Modulation” or PWM. The PWM is sent

through the control wire. These pulses are generated from either a microcontroller or

a timer IC. The servos maximum movement as a result of the electronic pulses is

from 0 degree to 180 degrees. If needed, the servo rotation can be achieved to be

depending on the manufacturing features. It cannot move further from 180

degrees because a mechanical stopper prevents it. The pulse is sent at an interval of

every 20 milliseconds (ms). The width of the pulses sent varies. It can be 1.0ms,

1.5ms or 2.0ms. A pulse of 1.0ms will rotate the shaft in an anticlockwise direction at

- , a pulse of 1.5ms will bring the shaft back at neutral position or and a pulse

of 2.0ms will rotate the shaft in a clockwise direction at + . This is the plane in

which the shaft will move. The following figure 16, illustrates the process of PWM.

Figure 15 PWM Process (Daware, 2017).

The shaft when applied the pulse will move to the required angle and hold its

position. The pulse must be repeated every 20ms for the shaft to keep its position. If

some other force is applied to the servo motor externally along with the pulses, it


resists that force to take its position. A servo is never idle and continuously keeps a

check to sense the input signals so that it can rotate accordingly.

3) Voltage converter: This is also called a voltage decoder. It is a circuit which

decodes the input pulse and then converts it into its corresponding voltage. As soon

as the circuit receives the input pulse, it charges the capacitor at a constant rate and

keeps charging it until the pulse is high. When the pulse goes low, the capacitor

discharges through the buffer amplifier and this negative feedback is then sent to the

error amplifier.

4) Error amplifier/voltage comparator: This is a negative feedback operational

amplifier and it receives input voltage from potentiometer and voltage converter and

compares it. The difference between these two input voltages is then amplified and

sent as feedback to the servo motor. The motor in turn rotates the pot shaft and the

servo shaft. When this voltage difference is more, motor will drive faster and when

difference is low, motor will be slower in speed. In the same way, direction of motor

will be controlled by the fact that if voltage difference is positive then it will move in

one direction and if the difference is negative then it will move in the opposite

direction.

5) Potentiometer: A potentiometer is used to sense the mechanical position of

the shaft through pot in the servo. The pot is the position sensor which senses the

rotational position of the servo shaft. Shaft of the pot is attached to motor shaft with

gears. Drive shaft and pot shaft rotate together thus changing its resistance.

Resistance at every angle that the shaft moves generates a corresponding voltage

which is then given as feedback to the error amplifier to decode and compare the

voltage.

6) Motor and Gear set: The servo motor receives the data about angle with its

polarity (positive/negative) from the error amplifier and then drives as a result of this

input. In servos available these days, sensors are used to sense the position of the

shaft. The gear assembly in a servo is used to reduce speed/ RPM (Revolutions per

minute) and simultaneously increase torque of the servo motor for rotation. The high

speed force of a servo motor is changed into torque by application of gears. In

physics, as a law; Work = Force x Distance. So, in servo motor when the force is less

than the distance (speed) is high and when the force is high then the distance is less.

The potentiometer calculates and stops the servo motor at the desired angle as

discussed earlier (Daware, 2017) (Robotplatform.com, 2017).


5.1.3.2 Applications of servos in today’s world

Servos can be used where a task needs to be performed repeatedly and in a

specific pre-defined way. Servo motors are a very useful device and they have found

vast applications in the fields of commercial applications as well as industrial

manufacturing. Servos are used to find cost-effective solutions to products so that

they are affordable for the end user. They make life in the twenty first century more

convenient and increase our quality of life. Some of the examples of their

applications are computers, robotics, mars rover, CD/DVD players, conveyor belts in

factories for product packaging/labelling, camera auto-focus, metal cutting and metal

forming machines, antenna positioning, automatic door openers, printing press or

printers, textile spinning and weaving machines, woodworking mechanisms, solar

tracking system for solar panels and robotic vehicles etc. (Tigertek.com, 2017)

5.1.4 DC motors

Micro Metal Gear motor MP 6V with Extended Motor Shaft

It is a small DC motor with a voltage of 6V with a 248.98:1 metal gearbox. It is

medium powered. The physical specifications of the micro metal gear motor are as

follows:

The gearbox is D-shaped.

Its cross section is 10 x 12 mm.

Its length is 9 mm.

Its diameter is 3 mm.

The gear motor has an extended shaft of 4.5 x 1 mm

The micro metal gear motor (shown below in figure 17) operates at 90 RPM and

40 mA with no load, 41 oz-in (3.0 kg-cm) and 0.7A at stall. These small brushed gear

motors are available in various gear ratios in a range of 5:1 to 1000:1. This gear

motor will be used for running the wheels of the Spicar hexapod.


Figure 16 DC Motor (Pololu.com, 2017)

5.1.5 Power Source

(Skylightupower.com, 2017)

(produktinfo.conrad.com, 2017)

For developing Spicar, two types of batteries were explored namely NiMH and

Lipo. NiMH battery (Nickel-metal hydride battery) was developed by upgrading NiCd

battery. NiMH is a cylindrical shaped battery as shown in figure below. It is filled with

hydrogen as its energy storage medium. The battery is closed with a lid made up of

an alloy of nickel with one more sturdy metal e.g. titanium, as shown below in figure

18.

Figure 17 NiMH battery structure (Skylightupower.com, 2017)

Lipo battery (Lithium polymer battery) is made up of Carbon element and

Lithium which has the chemical property of being highly reactive. This battery has a

flat shape which allows minimal resistance. This battery has the capacity to store a

lot of energy due to its properties. Lipo battery is shown below in figure 18.


Figure 18 LiPo battery structure (Skylightupower.com, 2017)

Now the two batteries were studied and the eight differences noted in the

following respects:

1. Cost: Presently NiMH battery is cheaper than LiPo in the market.

But if LiPo is produced in large numbers, the economies of scale

bring its price down.

2. Weight: In all radio control devices, the weight and size of battery

is a critical matter. As compared with NiMH, LiPo batteries are

smaller in size and less heavy.

3. Voltage: The voltage for each cell of LiPo battery is 3.7V so it

comes in 7.4, 11.1V, 14.8V etc. while NiMH battery has 1.2V for

each cell. NiMH is available in 3.6V, 7.2V etc.

4. Charge/Discharge: LiPo battery has an added advantage that it

can be charged / discharged in a short period of time. But it also

has the disadvantage that it can burst if over charged/discharged

so it has a safety hazard. NiMH is relatively safer in this regard.

5. Safety concern: LiPo batteries have a soft casing so they are

prone to physical damage while NiMH are better in this regard

because they have a strong hard casing.

6. Battery capacity: LiPo cell's battery capacity is much better than

NiMH. The capacity for Lipo is from 3.7V 800 mah to 3.7V 22AH.

Whereas the capacity of NiMH battery is from 2500 mAh to 3000

mAh only.


7. Battery charger: To make every LiPo cell balanced, LiPo battery

has its own specific chargers. But there are chargers available in

the market that can charge both LiPo and NiMH batteries e.g.

iMax B6.

8. Memory effect: LiPo batteries have zero memory effect while

NiMH can have voltage depression similar to that of NiCD

batteries.

Keeping all these factors in mind, LiPo batteries are much better than NiMH for

use in radio control cars, helicopters and robots. So, for “Spicar” robot also LiPo

battery was the obvious choice for its better performance. As Spicar was powered

using a “Rechargeable Li-Ion Polymer Battery”. It provides nominal voltage of 7.4 V

and nominal capacity of 450 mAh.

Figure 19 (LiPo) 7.4 V 450 mAh 40 C Conrad energy Stick

(produktinfo.conrad.com, 2017)

The Lithium-ion Polymer Battery (shown above in figure 20) can be stored for

short as well as long term. If the battery needs to be stored for longer than 3 months,


then it needs to be recharged from time to time to preserve it. It’s recommended to

store it at a temperature range of -10 degrees to +40 degree centigrade and a 45 to

85% RH if its stored for 3 months. But if it needs to be stored for a period longer than

3 months then the temperature range recommended is from 0 degree to +35 degree

centigrade. The voltage that needs to be maintained for this long time storage is in a

range of 3.7V to 4.2V for each cell in the battery. After storage when the battery is

used, its capacity recovery rate is 80% or even more sometimes when in the delivery

state which consumes 50% capacity of the fully charged battery

(produktinfo.conrad.com, 2017).

Table of Hardware components with their Specifications and Prices is given in

“APPENDIX C – Hardware Components and Prices”.

5.2 Software

Arduino is an open-source electronics prototyping platform based on flexible,

easy-to-use hardware and software. It’s intended for artists, designers, hobbyists,

and anyone interested in creating interactive objects or environments (Bruce, 2017).

All arduino boards are completely open-source, empowering users to build them

independently and eventually adapt them to their particular needs (Arduino.cc, 2017).

Ardunio, as a piece of hardware can be either used independently in a robot,

connected to a computer, or connected to other arduinos, or other electronics

devices and controller chips. In this project it will be connected to the Atmega2560

processor embedded in Dagu spider robot controller. Thousands of people and

organizations use it for smaller and larger level projects. The language that it

normally uses is Java or similar langugaes i.e C/C++. Based on previous experience

in C language, it has been chosen to be the language for this project.


6 Methodology

This section discusses the various suitable methods available to design

engineers and selection of most appropriate method for this project that ensures

reliability, efficiency and viability.

Methodology for this project must encompass developing the concept of the

product, research and literature review, design and development of mechanical,

electronics and software components, final testing and evaluation before release. A

number of relevant existing project methodologies are discussed below:

6.1 Software and Spiral methodologies

These methodologies when read and understood in greater detail, found out to

be more specifically designed for detailed software development (cms.gov, 2017).

Elaborating methodologies above and some other project methodologies i.e. agile

development, rapid application development, lightweight methodologies seem

irrelevant here. These methodologies do not fulfil all the requirements of this project

as this project is not a pure software development one; it involves development of a

physical product through hardware and software implementation.

6.2 Waterfall

Waterfall methodology is a sequential (non-iterative) design process which

demands that one task be completed before going to the next. This methodology

progresses through the phases of conception, initiation, analysis, design,

construction, software implementation, testing, integration, deployment (installation)

and maintenance as shown below in figure 21.


Figure 20 Waterfall Method (Bowes, 2017)

This methodology originated in the manufacturing and construction industries;

it’s basically a hardware-oriented model which has also been adopted for software

development.

6.3 Chosen methodology

As per the requirements of this project given above, this waterfall methodology

with flowchart approach and with slight modifications, to meet the requirements of

this project, is chosen to be the best. Methodology made for this project ensures

reliability, efficiency and viability of the project. It is summarized in bullet points

below:

Research the available locomotion systems for different robotic vehicles.

Set the required specification of the vehicle.

Design the vehicle in software and prove its functionality.

Build the actual system.

Test the robot.

Evaluate construction, design processes and functionality.

Write the final report of the project.

Flowchart given below provides a deep insight into project methodology:


6.3.1 Methodology Flowchart


Figure 21 Methodology Flowchart

After methodology this leads to the Control of Spicar robot which is given below.


7 Project Planning – Gantt chart

Gantt chart given below in figure 23, illustrates the estimated times to complete

the tasks within the project. Timing deadlines have been followed closely as there

were good number of tasks and activities encapsulated in the project. Ideally, tasks

were emphasized on their completion before the deadlines and the next task was

started as soon as possible to compensate the time for any particular task (i.e.

software implementation) that took a little longer than its scheduled time on the Gantt

chart. Although hardware arrived more than a month late but still other tasks were

started to avail the time that’s why the original Gantt chart designed was not

modified.

Log book/e-log was kept up to date and the literature review was prepared as

the project progressed through each task. Although the time for report writing was

allocated towards the end of the project but draft report writing was carried out at the

end of each task/activity. Draft report writing along with Log book/e-log definitely

proved out to be very useful towards the final report writing.

Meetings with the supervisor took place every week except in last month when

the weekly meetings were not required. Draft work (Progress summary) was sent to

the supervisor before every meeting for feedback and it was further discussed in the

one-to-one meeting. Minutes, tasks discussed and next week actions of each

meeting were recorded in logbook on weekly basis. Main milestones and

Deliverables of the project are listed below:

7.1 Main milestones of the project

Logbook / e-logbook

Meetings with supervisor

Project Research

Project Registration

Project Proposal

Interim Presentation Upload

Project Design and Development

o Walking locmotion

o Rolling locomotion

Testing & Evaluation

Project Report

Presentation and Poster

Final Product


7.2 Deliverables of the project

Project Registration & Project Proposal

Interim Report / Presentation

Log book

Physical product (Robot)

Project Report Gantt chart given below can be maximised, using zoom options, for clear view.

Figure 22 Project Gantt chart


7.3 Safety Assessment

Safety and other important assessments were fully conducted in “Project

Specification” chapter but some more technical safety assessments are also

elaborated here. Although this project does not involve any kind of serious risks, a

couple of safety measures, were defined and some were later observed during the

implementation stages, for better work execution towards the end of the project, are

given below:

To avoid eye strain and tiredness, frequent breaks were taken which were

important while looking at the PC for long periods of time.

To avoid battery leakage, the battery was always kept at room temperature.

Proper wires were used to avoid any burning or small fire explosions.

While testing the robot, keeping eye contact at least a foot away from the

robot was always maintained.

While drilling holes in the robot frame, don’t apply extra force as it breaks the

frame.

7.4 Ethical Considerations

Qualitative research conducted with friends, colleagues and lecturers is

completely anonymous; no names or any kind of personal data is kept for any

reason.


8 Spicar Control

To start with, it can be said that whole control relies on how efficiently the

servos and DC motors are controlled as these are driving the walking and rolling

locomotion respectively. Servos’ details and their mechanism are fully discussed in

section “5.1.3 Servos” & “5.1.3.1 Servomechanism”. DC motors are also discussed in

section “5.1.4 DC Motors”.

PWM has been discussed in detail in section “6.1.1 Servomechanism”. This

leads to PWM signal generation.

8.1 PWM Signal Generation

All microcontrollers have the ability to generate PWM (pulse-width-modulated)

signals. This process of PWM signal generation can be either engaging most of the

processor resources or less of it. When the microcontroller engages less of the

processor then it’s more costly to purchase because of the added hardware features

used for signal generation that in turn allow the processor to run other tasks. An

example of least processor using method is the type of microcontroller that is used in

Spicar. These microcontrollers have a PWM module embedded in them. There is a

chip on the microcontroller in which reside the control registers that carry information

regarding the duty cycle and period of the PWM signals that are created when the

PWM module is executed. Some electrical devices need a very large period e.g. a

servo motor which typically has a period requirement of 20ms. Now the PWM module

which comes with the microcontroller might not be able to produce a large sized

period because of the speed or type of microcontroller being used (Johns, 2017).

In order to produce a longer PWM signal, a more processor-intensive method

may be used. In this method, a pulse width variable is pre-set and a "count" is

manually compared to that variable and that determines the length of the pulse width.

If that count is higher than the variable then the pulse width signal is low. And if the

count is lesser than the variable then the signal is high. This PWM period will take the

same time as it takes to run the code. So loops are used to increase the time which

will in turn increase the length of the period. This whole process can be restarted by

resetting the count when the PWM period has passed.

8.2 Controlling the Servos and DC motors

(Johns, 2017)


Mostly servos, including the Tower Pro SG90 Micro Servo for Spicar, come with

three pins namely power pin, ground pin and a control signal pin. The control signal

is a PWM input signal and its high pulse width determines the angle which the servo

will take as a result as shown below in figure 24.

Figure 23 Servo's High Pulse Width determines the Angle Position (Johns,

2017)

The mechanism of the servo motor is such that the potentiometer creates an

internal signal and its pulse width is compared with the PWM control signal and as a

result of that the shaft angle is set. This angle will rotate the motor shaft. The chip on

the microcontroller controls the signal. This is the advantage of using the servo

motors. The servos are connected to the chip through current amplifying device

because these motors usually require 25mA of current to run.

The specifications that are usually needed to run a servo motor are such that

they need a pulse width between 0.9-2.1ms and the mean position is 1.5ms. That is

the average pulse width. The output shaft of the servo is positioned according to the

pulse width supplied. Typically a servo's maximum angle that can be reached is 180

degrees. Servos can change its position to a finite amount of angle in each cycle so

multiple cycles need to be sent for servo to take the desired position. If the servo

needs to cover more distance, its speed will be faster. So the relationship between


servo speed and target distance is directly proportional. The speed slows down as it

approaches its target location and finally stops when reaches the target.

As long as signal is sent, the servo will resist any change to detour from target

location. So a servo is controlled through signals and in their absence, it can be

moved freely in any direction. So, microcontrollers are an effective solution for

controlling servos while creating electrical devices, machines and robots. These

microcontrollers run on a relatively simple mechanism and they are not very costly.

Now through this concept of PWM signals, the servo motor shaft can be rotated at

different angles and thus employed in electrical projects. These PWM signals are

used in controlling analogue devices effectively (Johns, 2017).

8.3 Spicar Open-Loop Control

For the time being the Spicar cannot move on its own because it does not have

sensors that can provide immediate feedback about the type of soil or terrain that it’s

traversing. It is not provided with any kind of vision abilities either. While rolling on

wheels, it does not have a means to know whether its wheels will be stuck in the mud

or sand. As it does not have a feedback system yet, it needs to be told exactly what

to do. The Spicar does that by executing open loop control for a pre-set walking gait

and for rolling locomotion. This follows the programme flowchart for demonstration of

Spicar robot.

8.3.1 Programme Flow chart

The programme flowchart to demonstrate the walking and rolling locomotion is

given below in figure 25. The program was designed for Spicar to first perform

walking locomotion, starting with forward, backward, right and left movements

respectively. Then it stops for 5 seconds and legs then retract in slowly, lowering

Spicar onto wheels for rolling locomotion. In rolling locomotion it rolls forward, turns

left, rolls backward, turns right respectively and finally stops and here the Program

ends.


Figure 24 Program Flow chart

The ability of Spicar to gain feedback through sensors and thus become more

autonomous in its locomotion will be achieved in future work which is discussed at

the end. Spicar will be improved by the use of sensors. For the programming

purposes, microcontroller used in Spicar is Dagu spider robot Controller with

(ATMega2560 processor)

8.4 Dagu Spider Robot controller

Dagu Spider Robot controller has been used to implement walking and rolling

locomotion. How it implements these locomotions and controls the legs and wheels

of Spicar is given in their related sections “10.1 Walking Locomotion” and “10.2

Rolling Locomotion” respectively.


9 Hardware Implementation

Following the development of Control strategy, the hardware implementation

starts which includes design, assembly and hardware block diagram.

9.1 Design and Assembly

Since this project involved overseas manufacturers and suppliers, there was

delay due in shipping and delivery received was incomplete. Parts of the frame that

were ordered are given below in figure 26 and 27:

Figure 25 Robot parts

Figure 26 Robot


Important features of the frame:

6 DOF: flexible control, more movements.

Light weight: 250g (without servo).

Material: Imported acrylic, laser cutting, not easy broken.

Size: About 24(L)*18(W)*12(H) cm/

Durability: Safe and non-toxic.

Product delivered was incomplete with legs’ part (Tibia) and nuts & bolts were

missing. Legs’ “Tibia” part which was then designed in CAD software (Thomas, 2014)

is given below.

9.1.1 Legs design

9.1.1.1 Tibia

Tibia is also known as shinbone on the shank bone and it is one of the larger

and stronger portions of the leg which is situated below the knee joint. It bears most

of the weight of the robot body.

Tibia was designed after careful analysis of the test terrain and clearance of the

materials testing. The thickness of the leg is kept at 3 mm. This thickness was tested

on SolidWorks and cleared. This tibia is connected to the body with a femur and

bracket that fits into the robot body. The servo test revealed that the servos will have

enough torque to lift and balance the required weight at 90 degrees angle. So when

the leg is made at a 90 degrees angle, it will give 87.620 mm clearance space from

the servo to the ground on the leg. Our legs are built with 2 DOF. The centre of the

servo is kept in line with the centre of the foot of the leg so that the leg will be able to

evenly press down during its gait.

Tibia design including its dimensions, hole size (3mm) and final print out of leg

is shown below in figure 28 and 29.


Figure 27 Leg (TIBIA design in Thomas, 2014)

Figure 28 Tibia drawing and 3D print


9.1.1.2 Brackets

Brackets (shown below in figure 30) are used for joining the legs of the hexapod

to its body. Brackets allow the horizontal movements (forward and backward) of the

legs. The brackets came with package were designed in a way that even the thinnest

part is of 3mm thickness which is the safe limit for the resin being used. This also

provides space for the actuators to be easily joined or removed without opening other

parts of the hexapod. The mounting holes in the brackets are made such that an M3

screw can be placed in it and tightened with a nut at the back. M3 screws are the

size provided by the manufacturer to fix the horn of the actuator through its centre

slot.

Figure 29 Leg Brackets

9.1.1.3 Femur

The femur (shown below in figure 31) which is also known as thighbone is the

most proximal (closest to the centre of the body) portion of the leg. It is the strongest

portion of the body and is to connect the legs to the brackets and because of femur

the leg can move up and down (vertical movements) during its gait locomotion. The

actuator is the motor that is joined to the bracket and femur and due to this actuator

the femur and legs move in the desired gait. The femur is the support that holds the

weight of the hexapod and legs. The length of the femur is 4.2 cm. The torque rating

of the actuator depends on the length of the femur. e.g. if the torque rating is 9.5

kg/cm then the femur length of 4.2 cm will alter the torque rating to 2.3 kg-4.2 cm as

calculated below:

Torque rating =

= 2.3 kg-4.2 cm


Figure 30 Femur and “Femur Support”

Once the all the parts for walking locomotion were ready the rolling locomotion

implementation took place. For Rolling locomotion four wheels / brackets were added

based on the measurements taken for the base of the frame as shown in Figure 32

given below.


Figure 31 Spicar Base Measurements

At the base of the Spicar robot frame, back wheels were made active which

were fit with motors and two front wheels were made passive which were fit using an


axle and bracket. The base of the frame was fixed on plastic board using a white

tape in order to drill holes for brackets as shown below in figure 33.

Figure 32 Brackets, Wheels / Axle fitting for rolling locomotion

9.1.2 Spicar Assembly

It was now time to put all the parts together and complete the assembly. Spicar

was then assembled by placing and fixing all the componenets to their appropriate

places. Final assembly of Spicar is shown below in figure 34.

Figure 33 System Integration


Now the assembly was completed so that Hardware Block Diagram could be

drawn for Software Implementation to begin. Block Diagram is shown below in figure

35.

9.2 Hardware Block Diagram

Figure 34 Hardware Block Diagram

Diagram above elaborates the communication between Microcontroller and

other hardware components. Micrcontroller gives output signals to actuators. Instead

of using one servo for each wheel motor, only two servos are used in back wheels.

Front wheels are left passive and are driven by back wheels in order to save

resources. In processing part, Arduino (IDE) shows two way communications with

microcontroller. Two ways communication is because of sensors’ mechanism which

was an optional objective and is not achieved yet. In output section, Microcontroller

executes walking and rolling locomotions which included Forward and Backward

movements and Right and Left rotations. Sensors’ part is to feedback the output into

microcontroller for terrain navigation which is left for future work. Hardware

implementation follows software implementation given below.


10 Software Implementation

Following the hardware implementation, the software implementation was

started and gaits were made, analysed and finalised for walking locomotion. Then

open-loop control was developed for rolling locomotion.

10.1 Walking Locomotion

This locomotion, as previously talked about in Literature review, is most suitable

for uneven surfaces, especially in soft grounds or ground with obstacles where

wheels locomotion almost fails. This locomotion is achieved by using Forward or

Inverse kinematics. This section talks about Forward and Inverse kinematics,

discusses suitable gaits, analyses gaits, justifies a gait and develops kinematic logic

for its implementation in Spicar robot.

10.1.1 Inverse and Forward kinematics

Walking locomotion can be achieved using Inverse and Forward kinematics. In

inverse kinematic things are controlled on three levels:

1. The position (rotation) of each servo.

2. The position of the foot of the leg.

3. The movement of the robot’s body as a whole.

The command is given first at the highest level such as “Move Spicar Forward”

or “Rotate Spicar Left” and then each level below that does the right thing to

implement this command. For example the “Move Spicar Forward”, this means that

assuming a tripod gait in which first pair of three legs currently in the air move their

feet (tibia) forward and second pair of three legs touching the ground move their feet

backwards, this is how one step movement is performed.

The Forward kinematics is the complement of Inverse kinematic. It is operated

by answering, given the position of the joints in this leg, where is the foot? Whereas

Inverse kinematic is the opposite i.e. “given the position where I WANT the foot to be,

what position SHOULD the leg’s joints be in?” Inverse Kinematics involves a lot of

geometry and is suitable for implementation of different gaits at higher level. Forward

kinematic is easy and completely fine for this Spicar robot which at this stage does

not involve implementation of many different gaits.


10.1.2 Spicar Gaits

A hexapod robot (Spicar) can employ different types of gaits. Two basic types of

hexapod gaits are tripod gait and wave gait. These gaits are employed depending

upon the environment and the related requirements of the Spicar robot (Do, 2017).

10.1.2.1 Wave Gait

In the wave gait pattern of locomotion (shown below in figure 36), the Spicar’s

only one foot is raised in the air while the rest of the feet are firmly on the ground. In

wave gait, all the legs on one side of the robot are moved forward one by one,

starting the movement from the rear-most leg which is L3 or R3. The same

movement pattern is then repeated on the other side of the Spicar. Wave gait works

best for locomotion on rough surface (Do, 2017).

There are some disadvantages of the wave gate. Firstly, its speed is slow

because even if the programmer decreases the time of the robot’s leg lift, that will in

turn decrease the step. So speed will remain slow. Similarly if the speed of the

actuator is increased, then that will require increased amount of power which will put

extra load on battery and the control boards. If the delay phases are shortened, this

may result in colliding of the adjacent legs and collapse of part of the hexapod’s

body.

Figure 35 Wave Gait (Do, 2017).

10.1.2.2 Tripod Gait

Tripod gait is best suited for high speed of robot. In our robot “Spicar”, speed is

crucial for success in its missions. So tripod gait will be used mainly in it for

locomotion. In tripod gait (shown in figure 37), the set of front and hind legs move at

one side and on the other side the middle leg moves right opposite to it (L1, R2, and


L3). In the very next cycle, the pattern repeats in an alternating manner. In the tripod

cycle firstly three of the legs lift in the air to move forward and the rest of the feet

push the ground in the backward direction for support and moving forward. When

the next cycle starts, the Spicar will then shift its weight on the remaining feet and

then the movement pattern is repeated. In the tripod gait, the Spicar remains stable

because three of its feet are touching the ground all the time and it maintains this for

support (Do, 2017).

Figure 36 Tripod Gait (Do, 2017).

10.1.3 Analysis of the Walking Gaits

While developing walking locomotion, the main goal is to achieve smooth

locomotion and stable standing movement. Another problem is handling multiple

actuators at the same time when coding the prototype build.

It has been observed that the Spicar cannot stand properly or hold its position

when multiple actuators are run at the same time. It causes the actuators to shake.

Also the Arduino microcontroller has the drawback that it cannot run parallel

computing. It executes the commands one line at a time.

To take care of all these problems, creative coding should be applied. An

example of such coding is the use of for-loops which although do have a call for each

actuator that needs to be made, but they also have with it an incrementing variable

that adjusts their position. So when the call is made, all the actuators don’t act

simultaneously but with a slight time gap. Each actuator will keep adjusting itself

continuously independent of each other and their actions will be delayed from each

other by a time gap of milliseconds. In this way of working of the actuators, the Spicar


will be able to maintain a stable position and smooth locomotion. Consequently out of

these two gates, tripod gait is implemented as it offers best stability and locomotion.

10.1.4 Tripod, the Chosen Gait Implementation

This gait selection is a process (based on leg structure) for single leg to put

up and down according to a certain order or trajectory. Tripod Gait is a famous gait,

chosen for continuous stable walking motion. Legs are divided into two pairs of three

legs as shown in the picture below in figure 38.

Figure 37 Gait Selections (Pairs), (Liang, 2017)

When 1st pair lifts off the ground, the 2nd pair supports the robot body and

provides forward driving force for movement. Both pairs touch ground alternatively

(Liang, 2017). In order to understand how the walking takes place using this gait, let’s

analyse the figure given below in figure 39.


Figure 38 Common (Tripod) Gait and Stepping Sequence (McComb, 2017)

As shown in the figure 39 above, in its first sketch, black circle represents the

left middle legs on ground and white circle represents the right middle leg lifted off

the ground. Only one leg is on the ground at any time which makes the Spicar tilt to

the side opposite to the middle leg that is on the ground.

In power sweep sketch, Power drives the black circles (number 1s) legs’ pair

which is in contact with the ground. This sweep consequently propels the Spicar

forward.

In non-power sweep sketch, power does not drive white circles (number 2s)

legs’ pair which is lifted off the ground. Basically Spicar does not move in this step as

it merely positions the legs’ pair for the next sequence (McComb, 2017).


To summarise in power sweep mode legs’ pair (numbered 1s) does not make

movements, instead it stabilizes the Spicar on the ground and in the meantime in

non-power sweep mode, the legs’ pair (numbered 2) positions itself for the next

sequence and then this pair comes in contact with the ground when the other pair is

lifted at the same time which makes the Spicar finish one step movement.

There are 4 different kinds of walking operations that are achieved using these

pairs which are given below:

a. Walking forward

b. Walking backward

c. Walking clockwise (Right)

d. Walking Anticlockwise (Left)

10.1.4.1 Gait configuration and Pin selection for each Leg’s servos to Implement

Tripod gait:

Leg A: Fixed with servo 1 & 2 which are attached to pins 31 & 32

respectively.

Leg B: Fixed with servo 3 & 4 which are attached to pins 34, 35

respectively.

Leg C: Fixed with servo 5 & 6 which are attached to pins 37, 38

respectively.

Leg D: Fixed with servo 7 & 8 which are attached to pins 40, 41

respectively.

Leg E: Fixed with servo 9 & 10 which are attached to pins 43, 44

respectively.

Leg F: Fixed with servo 11 & 12 which are attached to pins 46, 47

respectively.

Entire logic developed in this section including Gate configuration and Pin

selection was used to develop the Code given in “Appendix A – Walking Locomotion

Code”. Picture of Pins attached to specified pins on microcontroller is given below in

figure 40.


Figure 39 Legs’ Servos attached to Pins on Microcontroller

Robot legs’ structure

~Front~

A=leg3, D=leg0

B=leg4, E=leg1

C=leg5, F=leg2

~Back~

Leg Pairs for Tripod Gate

1st pair: A, C & E or leg3, leg5 & leg1

2nd pair: D, F & B or leg0, leg2 & leg4

Movements

For Coxa = Shoulder

CCW = Counter clockwise

CW = Clockwise

For Femur = Knee

UP

DOWN

After studying and testing some code on Spicar robot, logic is developed on

which Spicar moves. There are two loops of two different phases as the Tripod Gait

works in a way that the two legs on one side and one leg on the other side move in


the same phase, while the other three legs move in the other phase at the same

time. Consider the graph shown below in figure 41.

Figure 40 Top View of Spicar

For instances, leg3, leg5 & leg1 are of the same phase (yellow circle) and leg0,

leg2 & leg4 are of the other phase (green circle). Let’s consider the leg on two

different sides in the graph shown below in figure 42.

Figure 41 Legs in loop motion


This graph is a draft of how the legs should move in the loop. The graph on the

left is the leg on the right side of the robot, which is viewing from the right side of the

body. The graph on the right is the leg on the left side of the robot, which is viewing

from the left side of the body. Axes directions are drawn in grey colour. The red dots

are end points of the leg and the black arrow indicates how the endpoint of the leg

should move in order to achieve the desired movement. A diagram of the actual

Spicar Robot moving its leg in loop A → B → C is shown below in figure 43 is as

follow:

Figure 42 Leg Motion

In this design, point B is the natural position of the leg, where point D is

vertically above the point B and point C & A are horizontally aligned with point D. In

other words, point B is standing position and point A and C are forward and

backward movement position respectively.

Walking Forward

So by analysing the graph shown above, we then figure out that we need two

different loops of steps to make this movement feasible. They are as follows:

Phase 1 (leg0, leg2, leg4): A → B → C → D → A

Phase 2 (leg3, leg5, leg1): C → D → A → B → C

The two different phases are assigned to the legs. The loop is a complete loop

which goes through every point as stated in the graph.

D

B A C


Walking Backward

It is basically the inverse of sequence of walking forward.

Phase 1 (leg0, leg2, leg4): C → B → A → D → C

Phase 2 (leg3, leg5, leg1): A → D → C → B → A

Walking Clockwise (Right)

For this case, it is pretty different from the above two directions. We can

consider the following graphs for design idea.

Figure 43 Loop of leg1 & leg4 when walking towards right

In this graph, shown above in figure 44, the loop of leg1 and leg4 when walking

towards right. The two legs are walking in the same direction. For the overview of all

the legs’ movements see the graph given below in figure 45.


Figure 44 Movement of each leg in their loop for Rightwards’ Walking

This graph above illustrates that how each leg should exactly move in their own

loop in order to walk rightwards. Therefore, deriving from this graph, we have the

following different loops.

Right side Phase 1 (leg1): A → B → C → D → A

Right side Phase 2 (leg0, leg2): C → D → A → B → C

Left side Phase 1 (leg3, leg5): C → B → A → D → C

Left side Phase 2 (leg4): A → D → C → B → A

Walking Anticlockwise (Left)

For walking leftwards, we can just invert the flow of walking rightwards.

Right side Phase 1 (leg1): A → D → C → B → A

Right side Phase 2 (leg0, leg2): C → B → A → D → C

Left side Phase 1 (leg3, leg5): C → D → A → B → C

Walking locomotion is complete now and this takes us to develop rolling

locomotion which starts below.


10.2 Rolling Locomotion

This method uses wheels for its locomotion, it’s a most common method of

locomotion used to maximise the speed of robot on even surfaces. In comparison

rolling locomotion (wheels) can carry extra load than walking or any other kind of

locomotion. Keeping the long rectangular frame of Spicar in mind, fixing two wheels

to its base became an impossible option for its locomotion. Four wheels were then

introduced for its smooth and fast rolling. Two wheels at the back of the base of the

frame were made active and two wheels at the front of the base were left passive.

Back wheels using high torque can drive front wheels efficiently enough.

Two back wheels were made active which drove the Spicar. One DC motor is

attached to each back wheel. Each Motor has its two “Positive” and “Negative”

terminals. “Positive” terminal when set to “HIGH” drives the motor in clockwise

(Forward) direction and Negative terminal when set to “HIGH” drives the motor in

anticlockwise (backward) direction. This helps develop logic for forward, backward,

right and left movements of Spicar using two back wheels. Movements are

elaborated below:

Rolling Forward

As shown below in figure 46, the code that positive terminals of both (left and

right) motors (“motor1_pos” and “motor2_pos”) are set to “HIGH” and negative

terminals of both motors (“motor1_neg” and “motor2_neg”) are set to “LOW”. This

drives the wheels in clockwise direction which means the Spicar moves “Forward”.

Figure 45 Forward Logic (APPENDIX B – Rolling Locomotion Code)

Rolling Backward


It is the inverse of Forward rolling, so for backward rolling negatives terminals of

both motors (“motor1_neg” and “motor2_neg”) are set to “HIGH” and positive

terminals of both motors (“motor1_pos” and “motor2_pos”) are set to “LOW”. This

logic drives the wheels in anticlockwise direction which means the Spicar moves

“Backwards”, as given below in figure 47.

Figure 46 Backward Logic (APPENDIX B – Rolling Locomotion Code)

Right Turn

In figure 48, shown below, the logic for Right and Left rotations is developed for

Forward movement only. So, in order to rotate Spicar in Right or Left direction, one

motor’s negative terminal and other motor’s positive terminal is made “HIGH” or

“LOW” and vice versa.

As shown in code given below, for Right Turn to take place while moving

Forward the positive terminal (motor1_pos) of Right Motor (which would be defined

as “motor1” in this case) is set to “LOW” and negative terminal (motor1_neg) is set to

“HIGH”, and for Left motor (which would be defined as “motor2” in this case) the

positive terminal (motor2_pos) is set to “HIGH” and negative terminal (motor2_neg) is

set to “LOW”.

When Spicar is moving backwards the motors would be defined the opposite

way, the Right Motor in forward movement becomes the left motor in backward

movement and vice versa for the Left Motor. So the negative terminal (motor2_neg)

of right motor (which would be defined as “motor2”) is set to “LOW” and positive

terminal (motor2_pos) is set to “HIGH”, and for left motor (which would be defined as

“motor1”) the negative terminal (motor1_neg) is set to “HIGH” and positive terminal

(motor1_pos) is set to “LOW”. This is how the Right Turn is achieved in backward

movement.


Figure 47 Right Turn Logic (APPENDIX B – Rolling Locomotion Code)

Left Turn

As shown in figure 49, given below, for Left Turn to take place while moving

forward, the logic used is exactly opposite to the logic used in Right Turn for Forward

movement or exactly same as the logic used in Right Turn for Backward movement.

And for the Left Turn to take place while moving backward, the logic adopted is

exactly opposite to the logic used in Right Turn for Backward movement or exactly

same as the logic used in Right Turn for Forward movement. The logic developed for

Left Turn is shown below.

Figure 48 Left Turn Logic (APPENDIX B – Rolling Locomotion Code)


11 Testing, Results and Evaluation

Thorough testing was focused through-out the design and implementation

phase. While testing, some difficulties were faced especially in the coding part. It was

hard to develop logic for gait; the movement of legs while maintaining stability of

Spicar.

Two types of testing were done for this project. First each instrument was tested

alone to check that it is functioning or not which is called as unit testing. Then comes

the combined testing after the system was integrated. This final testing was called

function testing. Now both types of testing are described in stages below:

11.1 Unit Testing

Each module in the application was tested while being developed to confirm its

adherence to the related requirements. This testing was done to check the working of

the components; unit testing was performed on servo motors, DC motors and

microcontroller.

11.2 Function Testing

The function testing was conducted to see the response of the whole system

which would further be demonstrated in Final Project presentation. Some functional

testing results are given below in Table 1.

COMPONENTS

CYCLE 1

CYCLE 2

FINAL

STATUS

Test for Atmega2560 Microcontroller

ports

OK

OK

OK

Test for Hardware Connections Failed OK OK

Test for Servo motors Failed OK OK

Test for DC motors Failed OK OK

Table 1 Function Testing Results

Hardware Connections, Servo motors and DC motors first tests failed because

hardware connections were wrong which were then figured out and made right.


11.3 Evaluation

Hardware assembly was a little challenging, at one point base of the Spicar

robot’s frame was cracked because of applying extra force while drilling a hole into it.

Luckily it was fixed perfectly to avoid any disappointments of ordering or designing a

new hardware. Final assembly came out to be perfect fix for rolling locomotion on

hexapod robot.

Software part included developing Algorithms and writing programmes in C/C++

language. This was the toughest part for the author. Finally author was able to

produce a code for walking locomotion and then the rolling locomotion which was a

lot easier than the code for walking legs.

11.3.1 Final Functionality

Spicar has demonstrated the walking and rolling locomotion as per the

designed program flowchart given in section “9.3.1 Programme Flow chart”. The

Spicar first performed walking locomotion, started with forward, backward, right turn

and left turn movements respectively. Then it stopped for 5 seconds and legs then

retracted in slowly, lowered Spicar onto wheels for rolling locomotion. In rolling

locomotion it rolled forward, turned left, rolled backward, turned right respectively and

finally stopped, here it terminated its demonstration. As per the objectives of this

project the Spicar is fully functional, although it can be improved to implement many

more gaits gates and other functions.


12 Discussion and Conclusion

The design and control of compact legged-wheeled robot has successfully been

accomplished. Spicar is a hexapod robot that looks like a bug. It’s was a fascinating

mix of hardware and software skills including aspects of mechanical engineering,

electrical engineering, robotics and control. This project was about developing a

hybrid robot that can perform walking and rolling locomotion depending on the

surface on which it navigates on.

All the objectives are met for the Spicar robot. First of all, extensive literature

review was carried out for legged, wheeled and hybrid robots that included hardware

components, the software and IDE (Integrated development environment for software

implementation).

- Suitable hardware for designing and developing the robot structure (chassis)

was determined that includes microcontroller, legs, wheels, sensors etc. Software

part was also determined which included Arduino as IDE for software

implementation.

- Legs of the robot were designed in CAD. Wheels were selected based on their

size and specification keeping in minds the dimensions of the robot. Robot chassis

was modified to include wheels for rolling locomotion.

- Electronic circuits were designed in which wheels, legs, actuators and

microcontroller were configured along with the other components. Then the hardware

was assembled to build and control a complete walking and rolling locomotion

system.

- Based on Spicar’s final assembly, the hardware block diagram was developed

in order to make algorithms (high-level description) to write final programs for the

software implementation.

- The Logics for Control Strategy of Spicar were then developed for walking and

rolling locomotion respectively.

- The microcontroller was then programmed with control strategy for manual

switch between walking and rolling modes.

- Now when the control has been achieved, the test plans were carried out. Two

types of testing were carried out for this project. Firstly unit testing was done in which

each module in the application was tested whether it fulfils the requirements or not.


Unit testing was done on Servo motors, DC motors and microcontroller. Then

function testing was carried out in which test plans were made to check functionality

of walking and rolling locomotion for the entire system integration. The robot was

then evaluated based on these tests.

In walking locomotion, the Spicar moves forward and backward at a speed of

one body length per second. It balances it's body mass and maintains a firm posture

with balance while moving forward, backward or sideways in rolling or walking

locomotion. It has provided with more generalised legged-wheeled robotic platform

that can manually be switched between legs’ and wheels’ mode. Spicar is made such

that it can be programmed easily for adding more types of movements depending

upon its functionality needed for any specific purpose. In future, this platform will be

modified to an autonomous robot by adding sensors. Sensors will be attached to map

the precise location of the Spicar and to navigate it to the desired position or location.

From there that work can be further expanded to include increasingly complex

motions (Gaits) and other interesting features. Due to its hybrid functionality, Spicar

can effectively be used for search and rescue, spying or space exploration missions.


13 Future Work

This project has developed a generalised legged-wheeled robotic platform that

can manually be switched between legs’ and wheels’ mode. It fully demonstrates

legged and wheeld locomotion.

In future this platform can be modified and programmed to an autonomous

robot to perform increasingly complex motions and functions. The Spicar project can

be improved in a number of ways. Firstly, it can be made autonomous by the use of

sensors. Making an autonomous robot was an optional objective for this project. One

week after the completion of this project, the author will work towards making Spicar

fully autonomous in a month's time. This can be done by the use of sensors that will

send feedback to judge the type of terrain that it’s going to traverse. This way Spicar

will be able to determine based on the feedback that which type of gait is best suited

for that surface or if required change its mode from legs to wheels or vice versa. E.g.

it should use tripod gait for strolling on smooth land while waive gait is suitable for

little uneven (rough) surface and on approaching complete flat surfaces i.e. roads it

can simply change it locomotion type from walking to rolling to maximise its speed.

Detailed research, given below, has been done on implementation of sensors to

make Spicar an autonomous vehicle.

13.1 Autonomous Control

Here the manual control will be upgraded to autonomous control. Walking and

rolling locomotion will be operated automatically using the range finder sensor(s).

When it’s fully implemented, the Spicar would roll on even surfaces to maximise the

speed and on approaching uneven surfaces (obstacles), as sensors will constantly

be sensing its path for obstacles, it will automatically switch to walking mode for

smooth stroll. Number of sensors can be used for Spicar that would improve the

precision and autonomous transition between its two locomotion systems. Closed

loop sensor feedback control system, as shown below in figure 50, will be used so

that the Spicar “know” what functions (movements) it is executing at all times.


Figure 49 Autonomous Spicar Closed Loop Feedback Control

This system uses the voltage sent into the controller as its input. The controller

then converts this voltage into a signal that will drive the motors on the robot, making

it perform locomotion. Sensors, encoders or vision system can be used to give

feedback to the controller that will keep Spicar aware of its surrounding, including its

direction and speed at all the times. Spicar at the movement is being executed

without any feedback system which makes it an open loop control system. This

follows the sensor configuration, selection and its implementation.

13.1.1 Sensor Configuration

13.1.1.1 Ultrasonic Range Finder Sensor

An ultrasonic range finder sensor is a very useful device for sensing sound to

measure distances. It is used to detect precise distances to an object or just to detect

when something is in range of sensor i.e. motion detectors. Best applications of this

sensor includes robotic navigations, object avoidance or for home/office security. Its

ability to use sound to find distances does not restrict it to find distances in darkness;

it equally works in light and dark.

This sensor utilises the propagation of high-frequency sound waves to detect

obstacles in its path. When sensor emits the sound waves, it hits the object

(obstacle) and its reflected off the object and back to the sensor. It then uses the

amount of time it takes for the wave to return back to the sensor and the speed of

sound to measure the distance of the object (obstacle) away from the sensor.

Formula used is: Speed = Distance / Time.

Re-arranging gives: Distance = Speed * Time.


The time variable (total time to of sound wave starting from leaving the sensor

and returning back to the sensor after bouncing back from the object) is calculated by

the ultrasonic range finder. Actually the time is divided into two parts as it is required

to only measure the distance from the sensor to the object and not the distance from

the sensor to the object and back to the sensor. The speed variable is the speed of

the sound wave at which it travels through the air.

The speed variable depends on temperature and humidity. Therefore, local

ambient temperature and humidity factor must be considered for accurate and

precise distance measurements. The formula for speed of sound in air with

temperature and humidity factor is given below:

C = 331.4 + (0.606 * T) + (0.0124 * H)

“C” is speed of sound in meters per second (m/s), “331.4” is speed of sound at

temperature 0 degree Celsius and at humidity 0%, “T” is temperature in degree

Celsius and “H” is % humidity (relative humidity).

13.1.1.2 SRF08 Ultrasonic Ranger

The SRF08 (shown in figure 51, is one of the advanced models of Ultrasonic

distance rangers. It comes with an excellent width-of-field detection, requires less

power to operate, its range to measure distances is wide enough from 3cm to 6m

and it can also be fitted with an LDR to measure light levels. This is one of the perfect

devices that can be used for projects requiring accurate ranging information. SRF08

uses I2C bus to communicate with microcontrollers.

Figure 50 Devantech SRF08 UltraSonic Ranger (coecsl.ece.illinois.edu, 2017)


As it uses I2C interface which means that 16 sensors can be chained up in a

single string. SRF08 comes with configurable addresses which makes it possible to

hook more than one address at a time in the same chain. Detailed specifications are

given below:

Range: 3 to 600cm (1.18" to 19.7')

Power: 5V, 15mA (typ), 3mA standby

Frequency: 40kHz

Size: 43mm x 20mm x 17mm tall (1.69" x 0.79" x 0.67 tall)

Connections: I2C

Analogue gain: Variable - 94 to 1025 in 32 steps

Light Sensor: Front Facing, value read/stored at each ranging request

Timing: Autonomous - no host controller timing required

Echo: Multiple echo - keeps looking after first echo

Units: Reports back range in microseconds (uS), mm, or inches

(coecsl.ece.illinois.edu, 2017).

This follows the I2C bus protocol that is used as a protocol to communicate

between the SRF08 sensor and microcontroller.

13.1.1.3 I2C Bus Protocol

I2C which stands for Inter-Integrated Circuit and pronounced as “I-squared-C”

or “I-two-C” is a serial protocol for two-wire interface, to further describe, it’s a multi-

master, multi-slave, single ended computer bus. It is used to connect low-speed

peripherals i.e. ICs to microprocessors and/or microcontrollers within short distances.

Implementation of I2C protocols requires no fees, however to obtain I2C slaves

addresses, one has to pay to NXP which allocates them.

The physical I2C bus has two wires SCL (Clock line) and SDA (Data line). SCL

is used to synchronise all data transfers over the I2C bus. SCL and SDA lines are

attached to all devices on the I2C bus. Third wire is also used here which is the

ground or 0 volts. Originally both SCL and SDA only give low output, to obtain high

output pull-up resistors must be attached with the lines to the 5V supply as shown

below in the figure 52.


Figure 51 Using the I2C Bus, SCL & SDA (Robot-electronics.co.uk, 2017)

If SCL and SDA lines are missing pull-up resistors, the outputs will always be 0

volts and consequently I2C bus will be non-functional. I2C bus has either masters or

slaves devices. Only master device(s) can drive the SCL clock line whereas slave

devices respond to the master. In this project, Atmega2560 is master and SRF08 is

slave device. Master and slave(s), both devices can transfer data over the I2C bus

whereas it is only controlled by the master.

In I2C physical protocol (shown below in figure 53), the master device

communicates with slave by issuing a start sequence on the I2C bus. I2C bus has

started and stop sequences (shown below in the figure). This is where SDA is

allowed to change while SCL is high. And when the data is being transferred, SDA

has to remain stable and not change whilst the SCL is high. The start and stop

sequences also mark the end and beginning of a transaction within the slave device.

Figure 52 Start and Stop Sequences (Robot-electronics.co.uk, 2017)

Data transfer (shown below in figure 54), takes place in sequences of 8 bits.

Every time the 8 bits are transferred to a device, it sends back an acknowledge bit

which shows that there are actually 9 SCL clock pulses to transfer each 8 bits of

data. How it further operates is that when receiving device sends back a low ACK bit

it means data is received and its ready to accept more data and if it sends back a

high ACK bit then it indicates that no more data can be accepted and the master

should stop the transfer by sending a stop sequence.


Figure 53 Data Transfer (Robot-electronics.co.uk, 2017)

I2C has a standard clock speed of up to 100 KHz. It has addresses which are

either 7 bits or 10 bits. This project uses 7 bits addresses which means that it will

allow up to 128 devices on the I2C bus as a 7 bit number can be from 0 to 127. To

send a 7 bit address, 8 bits are sent and this extra eighth bit is used to inform the

slave if the master is writing to it or reading from it. If the bit is 0, then the master is

writing to the slave and vice versa when the bit is 1.

The code researched for sensor implementation is also given in “APPENDIX E

– Future Work Further Research” This appendix also include a little bit more research

about further improvement on Spicar robot.

Another interesting feature that can be incorporated in Spicar is interfacing with

Android/ Apple iOS telephones through Arduino Mega 2560 board. This way Spicar

robot can be controlled through android/Apple iOS telephones by using their WI-FI or

Bluetooth technologies. Typical applications include would then include robust

Search & Rescue, reconnaissance, extra-terrestrial explorations etc.


14 References

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hybrid wheeled-legged robot - WheeHy - IEEE Xplore Document. [online]

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Robot-with-Servo-p-1029370.html [Accessed 7 Mar. 2017].

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[18] Skylightupower.com. (2017). 8 Difference Between Nimh vs Lipo Battery.

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2017].


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information-technology/xlc/downloads/selectingdevelopmentapproach.pdf [Accessed

19 Feb. 2017].

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[24] Johns, B. (2017). DESIGN AND CONTROL OF A NEW

RECONFIGURABLE ROBOTIC MOBILITY PLATFORM. [online]

Smartech.gatech.edu. Available at:

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ast.pdf?sequence=1&isAllowed=y [Accessed 15 Apr. 2017].

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[Accessed 26 Apr. 2014].

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2017].

[27] McComb, G. (2017). Build a 12-Servo Hexapod. [online] Robotoid.com.

Available at: http://www.robotoid.com/appnotes/project-build-12-servo-hexapod.html


[28] coecsl.ece.illinois.edu. (2017). Devantech SRF08 UltraSonic Ranger.

[online] Available at:

http://coecsl.ece.illinois.edu/ge423/DevantechSRF08UltraSonicRanger.pdf


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http://www.robot-electronics.co.uk/i2c-tutorial [Accessed 4 Apr. 2017].


15 Bibliography

[1] Nehmzow, U. (2003). Mobile robotics. 1st ed. London: Springer, pp.7-11, 25-

30.

[2] Bekey, G. (2005). Autonomous robots. 1st ed. Cambridge, Mass.: MIT

Press, pp.185-188, 199-203.

3 Br unl, T. (2008). Embedded robotics. 1st ed. Berlin: Springer.

[4] Van Sickle, T. (2001). Programming microcontrollers in C. 1st ed. Eagle

Rock, Calif.: LLH Technology Pub., pp.123-137.

[5] Predko, M. (2003). Programming robot controllers. 1st ed. New York:

McGraw-Hill, pp.42-47.

[6] Jones, J., Seiger, B. and Flynn, A. (1999). Mobile robots. 1st ed. Natick,

Mass.: A.K. Peters.


16 Appendix A – Walking Locomotion Code

// Fresh Code for 12 Servos Operation - Tripod Gate

// Author Zeeshan Mustafa Latif Ansari

// Institution: Birmingham City University

// BEng (Hons) Electronic Engineering

// Project: Design and Control of compact legged-wheeled robot "Spicar"

#include <Servo.h>

// #define TIBIA 45

#define DELAY 300

#define COXA_CCW 70 // CCW = counter clockwise

#define COXA_CW 100 //CW = clockwise

/*

~front~

A D

B E

C F

~back~

*/

#define UP1 92

#define DOWN1 125

int UP = UP1;

int DOWN = DOWN1;

Servo A_coxa;

Servo A_femur;

Servo B_coxa;

Servo B_femur;


Servo C_coxa;

Servo C_femur;

Servo D_coxa;

Servo D_femur;

Servo E_coxa;

Servo E_femur;

Servo F_coxa;

Servo F_femur;

void setup()

{

digitalWrite(31, OUTPUT);












pinMode(31, OUTPUT);













// pinMode(49, OUTPUT);

A_coxa.attach(31);

A_femur.attach(32);

// E_tibia.attach(33);

B_coxa.attach(34);

B_femur.attach(35);

// B_tibia.attach(36);

C_coxa.attach(37);

C_femur.attach(38);

// C_tibia.attach(39);

D_coxa.attach(40);

D_femur.attach(41);

// D_tibia.attach(42);

E_coxa.attach(43);

E_femur.attach(44);

// E_tibia.attach(45);

F_coxa.attach(46);

F_femur.attach(47);

// F_tibia.attach(48);

}


void loop() {

for (int i=0; i<=6; i++){

walkfwd();

}

for (int j=0; j<=6; j++){

walkbwd();

}

for (int l=0; l<=2; l++){

turnright();

}

for (int k=0; k<=2; k++){

turnleft();

}

}

void walkfwd()

{

// tibia();

f1();

f2();

f3();

f4();

};

void walkbwd()

{

// tibia();

b1();

b2();


b3();

b4();

};

void turnright()

{

// tibia();

r1();

r2();

r3();

r4();

};

void turnleft()

{

// tibia();

l1();

l2();

l3();

l4();

};

/* void tibia()

{

A_tibia.write(TIBIA);

B_tibia.write(TIBIA);

C_tibia.write(TIBIA);

D_tibia.write(TIBIA);

E_tibia.write(TIBIA);

F_tibia.write(TIBIA);

}

*/

// ~~~~~~~~~~fwd~~~~~~~~~~ //


void f1()

{

// [COXA] changed

A_coxa.write(COXA_CW);

C_coxa.write(COXA_CW);

E_coxa.write(COXA_CCW);

D_coxa.write(COXA_CW);

F_coxa.write(COXA_CW);

B_coxa.write(COXA_CCW);

delay(DELAY);

};

void f2()

{

// [FEMUR] changed

A_femur.write(DOWN);

C_femur.write(DOWN);

E_femur.write(DOWN);

D_femur.write(UP);

F_femur.write(UP);

B_femur.write(UP);

delay(DELAY);

};

void f3()

{

// [COXA] changed

A_coxa.write(COXA_CCW);

C_coxa.write(COXA_CCW);

E_coxa.write(COXA_CW);

D_coxa.write(COXA_CCW);


F_coxa.write(COXA_CCW);

B_coxa.write(COXA_CW);

delay(DELAY);

};

void f4()

{

// [FEMUR] changed

A_femur.write(UP);

C_femur.write(UP);

E_femur.write(UP);

D_femur.write(DOWN);

F_femur.write(DOWN);

B_femur.write(DOWN);

delay(DELAY);

};

// ~~~~~~~~~~bwd~~~~~~~~~~ //

void b1()

{

// [COXA] changed







delay(DELAY);

};

void b2()

{


// [FEMUR] changed




D_femur.write(UP);

F_femur.write(UP);

B_femur.write(UP);

delay(DELAY);

};

void b3()

{

// [COXA] changed







delay(DELAY);

};

void b4()

{

// [FEMUR] changed

A_femur.write(UP);

C_femur.write(UP);

E_femur.write(UP);





delay(DELAY);

};

// ~~~~~~~~~~right~~~~~~~~~~ //

void r1()

{

// [COXA] changed







delay(DELAY);

};

void r2()

{

// [FEMUR] changed




D_femur.write(UP);

F_femur.write(UP);

B_femur.write(UP);

delay(DELAY);

};

void r3()

{

// [COXA] changed








delay(DELAY);

};

void r4()

{

// [FEMUR] changed

A_femur.write(UP);

C_femur.write(UP);

E_femur.write(UP);




delay(DELAY);

};

// ~~~~~~~~~~left~~~~~~~~~~ //

void l1()

{

// [COXA] changed








delay(DELAY);

};

void l2()

{

// [FEMUR] changed




D_femur.write(UP);

F_femur.write(UP);

B_femur.write(UP);

delay(DELAY);

};

void l3()

{

// [COXA] changed







delay(DELAY);

};

void l4()

{

// [FEMUR] changed

A_femur.write(UP);


C_femur.write(UP);

E_femur.write(UP);




delay(DELAY);

};


17 APPENDIX B – Rolling Locomotion Code

// Date: 08th of May 2017

// Title: How to Control DC Motors Using Arduino

// Code by HackARobot in Arduino

// URL: http://www.instructables.com/id/How-to-control-DC-motors-using-

Arduino/

// Pins Controller Motors

#define motor1_pos 3 // Control pin 3 for motor 1_pos

#define motor1_neg 10 // Control pin 10 for motor 1_neg

#define motor2_pos 6 // Control pin 6 for motor2_pos

#define motor2_neg 9 // Control pin 9 for motor2_neg

#define motor_en A2 // Enable motor driver using anologue pin A2

void setup()

{

Serial.begin(57600); // opens serial port, sets data rate to 57600 bps

setupMotor();

}

void loop()

{

robotForward(1000); // Move Forward

robotLeft(1000); // Move Left

robotBackward(1000); // Move Backward

robotRight(1000); // Move Right

robotStop(500); //Stop for 5 seconds

}

void setupMotor() {

pinMode(motor1_pos,OUTPUT); // Configures motor1_pos (Pin) as output


pinMode(motor1_neg,OUTPUT); // Configures motor1_neg (Pin) as output

pinMode(motor2_pos,OUTPUT); // Configures motor2_pos (Pin) as output

pinMode(motor2_neg,OUTPUT); // Configures motor2_neg (Pin) as output

pinMode(motor_en,OUTPUT); // // Configures motor_en (Pin) as output

enableMotor();

robotStop(50);

}

//-----------------------------------------------------------------------------------------------------

// motor

//-----------------------------------------------------------------------------------------------------

void enableMotor() {

//Turn on the motor driver chip : L293D

digitalWrite(motor_en, HIGH);

}

void disableMotor() {

//Turn off the motor driver chip : L293D

digitalWrite(motor_en, LOW);

}

// Stop Robot //

void robotStop(int ms){

digitalWrite(motor1_pos, LOW);

digitalWrite(motor1_neg, LOW);



delay(ms);

}

// Move Robot Forward //


void robotForward(int ms){

digitalWrite(motor1_pos, HIGH);




delay(ms);

}

// Move Robot Backward //

void robotBackward(int ms){


digitalWrite(motor1_neg, HIGH);



delay(ms);

}

// Move Robot Right //

void robotRight(int ms){





delay(ms);

}

// Move Robot Left

void robotLeft(int ms){





delay(ms);

}


18 APPENDIX C – Hardware Components and Prices

Sr.

No

.

Componen

t

Function

Specification

Quanti

ty

Price

1 Robot

Chassis

DIY Six Feet Hexapod4 robot 6-

legged

6DOF (Degree of freedom)

Size: 24(L)*18(W)*12(H)

1 £27

2 Micro-

controller

Provide

control on

the Spicar

robot

ATmega2560 16MHz CPU

128K FLASH, 8K SRAM and 4K

EEPROM

70 I/O pins with male and female

headers

16 x 10bit analog inputs

15 x 8bit PWM outputs

1 £54

3 Servo

motors

For

movement

of Leg joints

Tower Pro Micro Servo 9g –

SG90

Dimensions: 22.2*11.8*31mm

approx.

Operation speed: 0.1 s/60 degree

Operating Voltage: 4.8 V (~5V)

Dead Band Width: 10 μs

Temperature range: 0°C - 55 °C.

12 £20

4 DC motors For

movement

of wheels

Size: 10 × 12 × 26 mm1

Weight: 9.5 g

Shaft diameter: 3 mm2

Gear ratio: 9.96:1

Free-run speed @ 6V: 2200 rpm

Free-run current @ 6V: 40 mA

Stall current @ 6V: 700 mA

Stall torque @ 6V: 3 oz·in

Extended motor shaft?: Y

2 £30


Motor type: 0.7A stall @ 6V (MP

6V)

5 Wheels and

brackets

Wheels for

rolling

forward &

backward

Wheels Diameter: 2.8mm 4 £2

6 Axle Rod for

wheels

Size: M5 1 £1

7 M3 nuts

and bolts

To tighten

robot parts

and wheel

brackets

Size: M3 20 £6

8 Battery To supply

power

1 £7

TOTAL

£147

19 APPENDIX D – Project Proposal

Project proposal is attached as a separate document because it was not copying

here properly; it was damaging the format of this report. Please refer to separate

document.


20 APPENDIX E – Future Work Further Research

20.1 Sensor Implementation Code:

///////////////////////////////////////////////////////////////

// Arduino ROBOT v0.1 //

// //

// http://www.educ8s.tv //

/////////////////////////////////////////////////////////////

#include <AFMotor.h>

#include <NewPing.h>

#include <Servo.h>

#define TRIG_PIN A4

#define ECHO_PIN A5

#define MAX_DISTANCE 200

#define MAX_SPEED 190 // sets speed of DC motors

#define MAX_SPEED_OFFSET 20

NewPing sonar(TRIG_PIN, ECHO_PIN, MAX_DISTANCE);

AF_DCMotor motor1(1, MOTOR12_1KHZ);

AF_DCMotor motor2(3, MOTOR12_1KHZ);

Servo myservo;

boolean goesForward=false;

int distance = 100;

int speedSet = 0;

void setup() {

myservo.attach(9);

myservo.write(115);


delay(2000);

distance = readPing();

delay(100);


delay(100);


delay(100);


delay(100);

}

void loop() {

int distanceR = 0;

int distanceL = 0;

delay(40);

if(distance<=15)

{

moveStop();

delay(100);

moveBackward();

delay(300);

moveStop();

delay(200);

distanceR = lookRight();

delay(200);

distanceL = lookLeft();

delay(200);

if(distanceR>=distanceL)

{

turnRight();

moveStop();

}else


{

turnLeft();

moveStop();

}

}else

{

moveForward();

}


}

int lookRight()

{

myservo.write(50);

delay(500);

int distance = readPing();

delay(100);

myservo.write(115);

return distance;

}

int lookLeft()

{

myservo.write(170);

delay(500);

int distance = readPing();

delay(100);

myservo.write(115);

return distance;

delay(100);

}

int readPing() {

delay(70);


int cm = sonar.ping_cm();

if(cm==0)

{

cm = 250;

}

return cm;

}

void moveStop() {

motor1.run(RELEASE);

motor2.run(RELEASE);

}

void moveForward() {

if(!goesForward)

{

goesForward=true;

motor1.run(FORWARD);


for (speedSet = 0; speedSet < MAX_SPEED; speedSet +=2) // slowly bring

the speed up to avoid loading down the batteries too quickly

{

motor1.setSpeed(speedSet);

motor2.setSpeed(speedSet+MAX_SPEED_OFFSET);

delay(5);

}

}

}

void moveBackward() {

goesForward=false;

motor1.run(BACKWARD);



for (speedSet = 0; speedSet < MAX_SPEED; speedSet +=2) // slowly bring the

speed up to avoid loading down the batteries too quickly

{

motor1.setSpeed(speedSet);

motor2.setSpeed(speedSet+MAX_SPEED_OFFSET);

delay(5);

}

}

void turnRight() {



delay(300);



}

void turnLeft() {



delay(300);



}

20.2 Research for Further Useful Improvements

Use Opto-Isolators, Why?, Detail, Justification and Recommendations. URL: http://www.arxterra.com/opto-isolator/

Use Voltage Regulator, Why?, Detail, Justification and

Recommendations. URL: http://www.arxterra.com/voltage-regulator/ Arduino Robot Project: A DIY obstacle avoiding robot using an SG90

servo and Ultrasonic Sensor. URL: https://www.youtube.com/watch?v=6TB0F_7SZHg URL for Code: http://educ8s.tv/arduino-robot-easy-diy-project/


Arduino: How To Build An Obstacle Avoiding Robot. URL:

https://www.youtube.com/watch?v=t3kXWSctj2Q How to connect a SRF05 to a SPIDER controller? URL:

http://www.robotshop.com/letsmakerobots/how-connect-a-srf05-a-spider-controller

design and control of compact legged- wheeled robot spicar · developed – term “spicar” is...

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