development of a 3d printable robot for use in education
TRANSCRIPT
Development of a 3D Printable Robot for use in
Education
Alexander Renken
Bachelor of Science in Mechanical Engineering
University of Nebraska – Lincoln
December 7, 2015
Abstract
This project analyzes the current field of educational robotics available for teach-
ing science, technology, engineering, and mathematics (STEM) to middle and high
school students. It then proceeds to purpose an original system with the target
demographics in Africa. This target demographic brings a unique challenge to de-
signing a product for education. Such challenges include feasibility of replacement
parts, access to tools, and availability of lesson materials. The final robot design
has taken into account all of these challenges. All of the parts are designed to be
3D printable. 3D printer technology is becoming cheaper and more ubiquitous in
schools. By making the robots 3D printable, if a part breaks, the school can simply
print a new one; no worry to buy a part from overseas and wait for it to be shipped.
The project resulted in the development of the AZIBOt. The name is a play on the
words azibo and bot; the word azibo meaning youth and bot being short for robot.
The robots are also completely Arduino compatible, making replacement electronics
available from many sources. The robot was designed to be completely assembled
with just one wrench and one screwdriver, both are included in the kit. Finally,
lesson plans have been made available online, free to use by anyone who wants to
learn about robotics.
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Contents
1 Introduction 1
1.1 Benefits of Robotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Current Work by SenEcole . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Framework 4
2.1 Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Other Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1 Makeblock mBot . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.2 AFRON . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.3 Sparki . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3 Proposed Concept 10
3.1 Design Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Design Restraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.3 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4 Design Approach 14
4.1 Electronics Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.1.1 Main Control Board . . . . . . . . . . . . . . . . . . . . . . . 15
4.1.2 Arm Servos . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1.3 Drive Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1.4 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
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5 Prototyping and Analysis 21
5.1 Chassis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2 Tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.3 Battery Lid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.4 Servo Lid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.5 Arm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.6 Full Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
6 Future Work 28
7 Conclusion 29
8 Appendix 30
8.1 Bill Of Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
References 31
List of Figures
1 Participants in the SenEcole 2015 Robotics Camp competing with
their robots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Participants in the SenEcole 2015 Robotics Camp in Dakar, Senegal . 4
3 Assembled mBot made by Makeblock, image from Makeblock website 6
4 Assembled MIT printable robot . . . . . . . . . . . . . . . . . . . . . 7
5 Assembled AERobot from Harvard . . . . . . . . . . . . . . . . . . . 8
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6 Educational Sparki robot made by ArcBotics . . . . . . . . . . . . . . 9
7 Romeo BLE board produced by DFRobot [9] . . . . . . . . . . . . . . 15
8 SB-GVS shield by Solarbotics [10] . . . . . . . . . . . . . . . . . . . . 16
9 Grove shield produced by Seeed Studio [11] . . . . . . . . . . . . . . . 17
10 Freaduino Uno produced by ElecFreaks [12] . . . . . . . . . . . . . . 17
11 SpringRC servo used as the drive servos from Pololu . . . . . . . . . . 19
12 Left: Top of the hunt sensor. Right: Bottom of the hunt sensor [14] . 20
13 Octopus push button from ElecFreak [15] . . . . . . . . . . . . . . . . 21
14 Ultrasonic range finder from ElecFreak [16] . . . . . . . . . . . . . . . 22
15 Rendering of the chassis subassembly . . . . . . . . . . . . . . . . . . 23
16 Left: Rendering of a single link Right: A full track of 34 links . . . . 25
17 Rendering of the battery lid subassembly . . . . . . . . . . . . . . . . 25
18 Rendering of the servo lid subassembly . . . . . . . . . . . . . . . . . 26
19 Rendering of the arm subassembly . . . . . . . . . . . . . . . . . . . . 27
20 Rendering of the fully assembled robot . . . . . . . . . . . . . . . . . 28
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1 Introduction
SenEcole is the outreach branch of the Nano & Micro Systems Research Lab at
the University of Nebraska – Lincoln led by Dr. Sidy Ndao. Dr. Sidy Ndao has
done extensive outreach both locally and internationally. His main focus is teaching
science, technology, engineering, and mathematics (STEM) throughout Africa [1].
To expand SenEcole’s capabilities in Africa, the Nano & Micro Systems Research
Lab has undertaken developing a robot for use in African classrooms. While African
classrooms are the target demographic for this project, the same robot platform
could be used to teach robotics in any classroom in the world that has access to a
computer and the internet.
1.1 Benefits of Robotics
There are many real world applications from what can be learned through robotics.
The most obvious include programming and electronics, but there is much more to
programming a robot then just code. Programming a robot is different than pro-
gramming a program that just runs on a computer. Programs that run on a computer
do the same thing every time. Programming a robot has unique challenges of work-
ing with the real world. The robot may act a little differently based on different
conditions. If its batteries are low, it will move a bit slower, if the lighting isn’t
consistent, then the line sensors may read differently. These challenges of working
with real world problems help programmers develop a host of valuable skills.
These include skills specific to robotics such as sensor characterization along with
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much broader skills such as problem solving and critical analysis. By learning to char-
acterize a sensor, students learn the importance of working with real world products,
products that are not perfect, and how to best utilize them. By programming sys-
tems that have imperfect sensors, students are challenged to come up with ways to
work reliably. Further, programming teaches critical analysis. Students must pro-
gram their robot, test it to see what it does, and then modify the code to make the
robot do exactly what they want. Looking at what the robot does and figuring out
why it is doing what it is based on the code is a great way to learn critical analysis.
Finally, basic electronics skills can also be taught with robotics such as the difference
between an analog and digital signal. An example of students testing their robots
can be seen in Figure 1.
Figure 1: Participants in the SenEcole 2015 Robotics Camp competing with theirrobots
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Technical skills are not the only thing learned through robotics. Students must
learn to work in teams to program their robot. This skill is invaluable as nothing
is designed in a vacuum. By challenging students to look at the world around them
along with providing them the means to learn, these students can gain self confidence
in their ability to change their world for the better. By working through the robotics
lessons, then applying them to their own projects, we hope to instill an "I can do
this" attitude in the students encouraging them to choose a career in STEM.
1.2 Current Work by SenEcole
SenEcole has already been working with teaching STEM in Africa. This includes
teaching robot camps and holding robotics competitions. Previously, Dr. Sidy Ndao
has gone to Dakar, Senegal to show of robotics like a six wheels remote control
robot along with a bi-pedal robot. While he was there, he also taught robotics
camps teaching hands on experience with hardware and software. The goal of these
camps is to help children develop critical thinking and problem solving skills, develop
teamwork, understand physical concepts of science and math, and to encourage them
to pursue a career in STEM. A group of participants from 2015 can be seen in Figure
2.
Previous camps have used the Makeblock line of robots along with Lego Mind-
storm to teach robotics. This includes the ongoing PARC or Pan Africa Robotics
Competition, during which, kids are challenged to use STEM to solve real world
problems [2]. This competition involves a research project portion where kids pre-
pare a poster and give an oral presentation along with a programming portion where
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Figure 2: Participants in the SenEcole 2015 Robotics Camp in Dakar, Senegal
kids program robots to accomplish specified missions.
2 Framework
This section reviews the scope of the project. It will outline the goal for both the
robot’s capabilities along with the long term teaching goals. It will also outline any
assumptions made regarding the end user. Competing systems will be identified to
show current options for educational robotics.
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2.1 Infrastructure
Currently, some schools have access to computers and the internet, but lack funds to
buy robots or software. The long term objective for this project would be to bring
robotic education to all of Africa, but the initial tests will be in Senegal. As of June
2015, 22.9% of Senegal has access to the internet with 27% of Africa as a whole having
internet access [3]. Assuming that a computer is prerequisite to internet access, then
at least 22.9% of Senegal must have access to a computer. All programs for this
project can also be loaded onto either a compact disk or a flash drive allowing for
computers that do not have internet access to still participate in the program.
2.2 Other Systems
There are current systems that are targeted to education generically and specifically
to education in Africa. There is a wide variety in price, capabilities, lessons, and
beginner friendliness. This section will look at a wide variety of systems that are
currently available and rate them on the aforementioned characteristics along with
commentary of other features that make each unique.
2.2.1 Makeblock mBot
The mBot is a robot designed by Makeblock for STEM education for kids [4]. The
robot uses a bent sheet metal chassis. It is driven by two DC motors. It comes with
with a light sensor, button, infrared receiver, ultrasonic sensor, and line follower.
For outputs, it has a buzzer, RGB LED, infrared emitter, and two motors. The
controller board that comes with the robot has four ports for additional sensors
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but other boards are available with more ports. Likewise, other sensors to expand
the capabilities of the robot are available for additional costs. The whole robot is
available for $74.99 USD with all teaching resources available online for free. An
assembled robot can be seen in Figure 3.
Figure 3: Assembled mBot made by Makeblock, image from Makeblock website
This robot seems to have done some things very well and others very poorly.
There are only 38 parts to assemble making it easy and quick to assemble. They
have also provided many means to program it and all of the software is free to
download. However, out of the box, there is no room for expandability, all the ports
on the controller are used. Users have also reported trouble downloading the drivers
to program the robot and that some of the curriculum to learn about the robot is
missing from the repositories.
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2.2.2 AFRON
AFRON is short for the African Robotics Network. While they do not directly pro-
duce a robot, they do promote robotics in Africa and have promoted the development
of cheap robots for educational use. Some of the projects that have resulted in from
their efforts are quite inspiring for basic robotics. Their goal is to produce a robot
with a unit price of $10 USD that can be programmed through a USB cable sup-
ported by open source software [5]. One such robot resulting from these efforts is
the MIT Printable Robot, seen in Figure 4.
Figure 4: Assembled MIT printable robot
This robot has an estimated unit price of around $20 USD and is constructed by
cutting out thin plastic sheet, folding it, and assembling it. It has an Arduino Pro
Mini as its control board making it comparable with any software that can program
an Arduino [6]. It is limited in its inputs and outputs with only a photosensor as
an input and two servos and an LED as outputs. Further, its design does not lend
itself well to expandability. The use of plastic sheet is well chosen though because
its wide spread availability and it being easy to work with. While MIT does provide
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some instruction, the lesson are quite limited and not well structured.
Another robot from the same AFRON challenge is the AERobot, short for Af-
fordable Education Robot, made by Harvard. With a unit price of just $10.70, teh
AERobot is the cheapest robots reviewed. It achieves such a low price by using
a double-sided custom printed circuit board with only two vibrating motors as its
mechanical parts. To further reduce price, the USB programming port is built into
the robot so that it can be plugged directly into the computer, no cable needed [7].
This custom robot can be seen in Figure 5.
Figure 5: Assembled AERobot from Harvard
The robot only has two sensors, a distance sensor and a photosensor, but the
curriculum makes good use of these two sensors. It covers basic programming con-
cepts like if statements and variables along with how to move, how to detect a bump,
line sensing and light following. They utalize a graphical program to program the
robot, making it easy for beginners. Unfortunately, this leads to little room for
expandability or use of other, more advanced means of programming.
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2.2.3 Sparki
Sparki is an educational robot produced by ArcBotics retailing for $149.00 USD.
Sparki is an Arduino compatible robot that has lots of built in sensors and is com-
patible with a custom, enhanced version of Arduino or miniBloq, a drag and drop
style program. Sparki has an impressive array of sensors including a distance sensor,
line sensors, IR emitter and detector, a buzzer, and Bluetooth. This allows Sparki
to do a lot of tasks. All these sensors are backed by extensive lessons. This Sparki
can be seen in Figure 6.
Figure 6: Educational Sparki robot made by ArcBotics
Sparki is also sold pre-assembled. Though Sparki has a good range of sensors, it
has very little room for expandability. Additional sensors can not be added and the
chassis is not modular, not allowing for additional capabilities.
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3 Proposed Concept
This section outlines the design parameters used to model the AZIBOt. This includes
desired capabilities, and the general form of the robot. It will also include design
restraints, including things we decided against doing because of manufacturability
or because it was deemed unneeded.
3.1 Design Features
The most important feature AZIBOt needed was it had to be completely usable
by children of at least middle school age (at least 12 years old). This includes
everything from assembling the robot, making all the correct electrical connections,
to characterizing its features and programming it to interact with the world. This
created design challenges for both the mechanical form of the AZIBOt along with
electronic and programming language selection.
The next important feature of the AZIBOt is that it needed to be modular. A
modular design was desired so that the kids could learn from the original kit, then
have parts that they can add on or take of to fit their needs. If they wanted to use
an IR receiver, which is not included in the basic AZIBOt, they should be able to
attach one easily. This expandability allows for the AZIBOt to be used as a platform
that can eventually teach more than just what it comes with.
This modular design also works the other way. The parts selected to build the
robot should also be able to be used in other projects, allowing the students to build
their own robots from the same basic parts. Future kits could also use parts from
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the AZIBOt kit keeping the price down for other educational resources.
This modularity and expandability is what would make the AZIBOt stand out
from the other robot kits discussed above. The Sparki and the robots produced
by the AFRON challenge have very limited expansion capability. The mBot, does,
however have some basic expansion capability, but it requires purchasing another
controller board, and even then, the user is limited to eight inputs and outputs. For
the AZIBOt to be a platform that could be built upon, it needs more inputs and
outputs, enough that it will take the user a long time before they use them all.
Other desired features include tracks for mobility and a robot arm to allow for
manipulation of the world around the AZIBOt, not just interaction with. The tracks
were chosen over wheels, partially because it kept the turning about the center of
the robot and allowed the robot to cover slightly rougher areas than wheels could.
There is also a sort of "cool" factor about tracks that make them more interesting
than wheels. Should the end user desire wheels over tracks, AZIBOt’s modularity
allows them to make the change very easily.
Some basic sensors were also desired. This includes a distance sensor for detect-
ing objects in front of the AZIBOt, two line sensors under the robot for detecting
contrast, allowing for edge detection and line following, and a button, allowing for
basic human input.
3.2 Design Restraints
There were a constraints when designing the AZIBOt, some of them were based
on manufacturability, while others were based around what we did not want the
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AZIBOt to become. Primarily, the AZIBOt is not a toy. This isn’t to say that it
isn’t designed to be fun, but it is much more than just a toy that roves around, it is
an educational tool. This means that the design needs to allow kids to learn about
robotics and programming from using it. It also needs to grow as the student grows,
allowing them to keep learning.
The AZIBOt should not be complicated to assemble. This project is set to design
a robotics platform for kids as young as middle school. This means that the parts
need to fit together nicely and be easy to assemble. Reducing the number of tools
required for assembly is one method to achieve this. Reducing the different types of
hardware also simplifies assembly.
The desired method of manufacturing the parts for the AZIBOts is 3D printing.
This method of manufacturing is chosen because it is good for small volume parts. As
3D printers become more commonplace, it will be easier for users to print their own
parts should they break on, or to even print a whole robot themselves. This means
that AZIBOts can be produced where ever there are 3D printers. Parts should then
be designed to be 3D printed. Designing for 3D printing allows for minimization of
post processing, making the final parts look better, print faster, and use less material.
3.3 Assumptions
Some basic assumptions about the end user were made regarding their skills and
resources. The students are not expected to have any previous programming expe-
rience. This assumption implies that the lessons designed to teach the students to
use the AZIBOt should cover each topic throughly, so that one that doesn’t know
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anything about the subject would still be able to work their way through the lesson.
The students will require access to a computer. As mentioned in Framework,
22.9% of Senegal has access to the internet. Computers, being a prerequisite for
internet access, are then accessible to at least one in five people in Senegal. While
internet access is preferred, the user could also install the required software from a
flash drive or CD.
3.4 Applications
AZIBOt is an educational robotics platform, but it is hoped that it can be used
for learning much more than programming. Other areas that can be learned about
through the AZIBOt platform includes, physics, kinematics, robotics, embedded sys-
tems, algorithm analysis, and boolean logic.
The most basic thing learned in physics is the relation between acceleration,
velocity, and displacement. The AZIBOt platform, with its controllable speed, can be
used to teach all three of these. It could be programmed with a specific acceleration
curve showing the relation between acceleration and velocity. If set to a specific speed,
the AZIBOt will demonstration the relation between velocity and displacement. The
robot can also show other physical concepts on a more qualitative level such as
torque, demonstrated by the arm. Kinematics can also be studied through the use
of the robot arm. This includes figuring out where the gripper will be if the joints
are positioned at specific angles. The torque required for each motor could also be
calculated by more advanced students.
Students will also learn a lot about robotics such as the challenges of working with
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real world systems. This included characterizing sensors to make their output more
useful and working with systems that react differently at different battery levels.
Once the students move from graphical programming to high level programming,
they will learn more about using embedded systems, including the limitations of
using a smaller processor.
By writing their own programs, students will be challenged to find ways of de-
tecting the world around them. Some ways will be more efficient than others. By
striving to find the best way to interact with the world, students will learn about
algorithm analysis. By creating these algorithms, the students will also have to work
with the inputs from the robot. Reading multiple inputs at a time is the basis of
boolean logic.
4 Design Approach
This section discusses the design process for the mechanical parts and electronics
selection.
4.1 Electronics Selection
This section covers the selection of the main control board, servo motors, drive
motors, and base sensors.
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4.1.1 Main Control Board
The first consideration was what board to use for the main controller. All boards
considered were Arduino compatible. This was decided because most graphical pro-
gramming systems are based on Arduino and more advanced users can then switch
to Arduino programming when they outgrow the graphical programming system. A
standard Arduino was not used in order to make the wiring portion much easier for
the kids. Wiring sensors can be complicated to understand and leads to a lot more
places for error. Four main boards were considered.
The first board considered was the Romeo BLE made by DFRobot. It has a lot of
features including a built in two channel motor controller, five buttons, eight analog
pins, and Bluetooth. It also has all of the pins broken out into male, female, and
ground, voltage, signal (GVS) style headers. It retails for $39.50 USD. The board
can be seen in Figure 7.
Figure 7: Romeo BLE board produced by DFRobot [9]
The next option considered was the the SB-GVS shield by Solarbotics. It retails
for just $13.95, but it is a shield, so it needs an Arduino to support it. It breaks out
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12 of the 14 digital pins and all six of the analog pins on a standard Arduino to a
GVS style header. It does, however, lack many of the other features that the Romeo
BLE has. This option was not chosen because of the additional cost of the Arduino
board and lack of unique features. This shield can be seen in Figure 8.
Figure 8: SB-GVS shield by Solarbotics [10]
The third option considered was the Grove shield by Seeed Studio. It also breaks
out seven digital pins, four analog pins, the UART, and four I2C headers. The
headers used are not the standard GVS headers, but rather, headers with four pins.
This shield was considered because there is a series of sensors built to interface with
it. This makes wiring very easy. It is also cheaper than the SB-GVS shield at $8.90.
Ultimantly, this board was not chosen because there isn’t an easy way to hook servo
motors up to it, a crucial part of the AZIBOt design to move the arm. The Grove
shield can be seen in Figure 9.
The board that got selected for this project is the Freaduino Uno by ElecFreaks. It
is a standard Arduino Uno close, except it has all the digital and analog pins broken
16
Figure 9: Grove shield produced by Seeed Studio [11]
out into GVS headers and a 3.3 volt or 5 volt selection switch. The Freaduino
is significantly cheaper than the Romeo BLE at $24.00 USD and has a simpler
construction, making it easier to use. It is capable of connecting more sensors and it
doesn’t use a proprietary set of sensors like the Grove shield. It gives the functionality
of a the SB-GVS shield at a lower net price. The Freaduino can be seen in Figure
10.
Figure 10: Freaduino Uno produced by ElecFreaks [12]
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4.1.2 Arm Servos
The desired robot arm had two joints and a gripper for a total of three servos. Based
on the expected size of the AZIBOt, standard size servos were chosen for the shoulder
and elbow servos. Originally a micro servo was chosen for the gripper servo, but this
was later revised to a standard servo for two reasons. The first is that the gripper
would have much more gripping strength with a standard sized servo. The second
is that it means there are fewer unique parts. Fewer unique parts make sourcing
parts easier and limits the number of parts that may need replacing. A generic
standard size servo was chosen. It has a full metal gear train which limits the chance
of stripping gears, but, realistically, any standard size servo would work.
4.1.3 Drive Motors
Hobby electronics often use three different types of motors to move, DC motors,
brushless motors, and servo motors. Brushless motors were not considered for this
project for a few reasons. The first is that they would require extra, comparatively
expensive electronics to drive them. They also spin at too fast of a speed to make
them practical for use in such a small robot without a gearbox. Adding a gearbox
would add cost.
DC motors, on the other hand, often come with gearboxes and the additional
circuitry to run them is relatively cheap. The Romeo BLE even has the needed
circuitry built in. The problem with their additional circuity is that coding it is
harder harder than coding for a servo motor. Many graphical coding programs do
not support motor drivers. Both DC motors and brushless motors also often require
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a second power supple further adding costs.
Servo motors were chosen for the reasons that the others were not. They are easy
to program and a lot of graphical coding programs support them. They are easy to
hook up to the Freaduino since they have a GVS connector. Continuous rotation
servos are commonly used in hobby robots for these same reasons. The SpringRC
SM-S4303R continuous rotation servo was selected because they are relatively cheap
while still outputting 45.91 oz*in at 43 RPM [13]. This servo can be seen next to a
US quarter for scale in Figure 11. These servos are the same size as those used in
the arm.
Figure 11: SpringRC servo used as the drive servos from Pololu
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4.1.4 Sensors
The AZIBOt has four main inputs, two line sensors, an range sensor, and a button.
The line sensors and button were chosen from ElecFreaks line of sensor modules called
Octopus Sensors. They were chosen because they are nicely mounted on perforated
circuit boards (PCB) and have connectors that break out their signal to the GVS
style header making them easy to connect to the Freaduino. They output a digital
signal depending if they are on a light or dark surface. They also have a small
potentiometer that controls the threshold between light and dark. This sensor can
be seen in Figure 12.
Figure 12: Left: Top of the hunt sensor. Right: Bottom of the hunt sensor [14]
The button is from the same line of sensors. It too has a connector allowing for
easy connection to the Freaduino and outputs a digital signal. The button used can
be seen in Figure 13.
The range finder selected for the AZIBOt was an ultrasonic range finder. Infrared
range finders were also considered because they use a GVS header outputting an
20
Figure 13: Octopus push button from ElecFreak [15]
analog signal, but they have a very limited range compared to the ultrasonic range
finder and are several times more expensive. The ultrasonic range finder selected has
a range from 2 centimeters to 450 centimeters. It does not use the GVS header, but
the provided cable still makes it easy to hook up to the Freaduino. ElecFreak also
provides a sample function to convert the reading to a distance. This function will
be added to the graphical coding program for easy interface. The ultrasonic range
finder can be seen in Figure 14.
5 Prototyping and Analysis
This section covers the design of each of the subassemblies along with how all the
subassemblies come together to form the whole robot. It will discuss design consid-
erations for the parts and highlight interesting or unique features.
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Figure 14: Ultrasonic range finder from ElecFreak [16]
5.1 Chassis
The chassis was the first part of the robot designed. It was designed to be as compact
as possible to minimize the size of the robot. The battery compartment is sized so
that the battery holder will fit in it with just a little bit of clearance. The height
of the chassis was determined by the thickness of the servos because they are the
thickest parts in the chassis. The two compartments are separated by a middle
divider. On each end and on each side of this divider is a small ledge for the lids to
sit on and some holes so screws can hold the lids in place. The divider has a hole
in it that allows wires to pass from one side to the other. The sides of the hole are
sloped at 45◦ because this allows the chassis to print without using supports here.
These features can be seen in Figure 15.
The servos are mounted directly to the chassis. This means the mount hole
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placement was critical to getting the servos to fit well. At first, the holes were too
low and small, so they were raised and opened up a little. The servos are held in
place with half inch long #4 machine screws. This is one of two sizes of machine
screws used on the AZIBOt. The flanges on the servos are also placed on the outside
of the chassis to make more room in between them for the line sensors.
Figure 15: Rendering of the chassis subassembly
The line sensors are set between the servos one inch apart. This distance was
chosen so that they could either straddle a line or have one sensor on it and one off of
a line made with electrical tape, which is often three quarters of an inch wide. They
each have a hole for the infrared emitter and detector to fit through and another
hole to mount them to the chassis with a screw.
The next sensor to get placed was the distance sensor. Holes the correct size for
its emitter and detectors were placed in the front of the chassis. A relief was put into
the ledge for the lid for the servo side to allow the sensor to be flush with the side
of the chassis. The mount holes in on the PCB were to small to use with practical
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screws, so the distance sensor is held in place by the servo lid. The ultrasonic sensor
is positioned so that the top of it is flush with the top of the chassis, taller than the
ledge. The servo lid has a recess in it that holds the ultrasonic sensor in place.
The last feature of the chassis is the rear wheel mounts. The offset the rear
wheels from the chassis to make them coplanar with the wheels mounted to the
servos. Originally, these were not flush with the bottom of the chassis, but they were
redesigned to be flush with the bottom to remove the need for support material while
printing. These mounts also have a hexagon recess in them to trap a nut so that the
screw for holding the rear wheels in place can be inserted easier without a wrench.
This also prevents the screws from entering into the battery compartment.
5.2 Tracks
The tracks were the next system designed along with the wheels. The tracks needed
to be designed so that they could not not slip off the wheels and so that the wheels
could apply force to them. A single link is seen in the left image of Figure 16. The
two flanges interface with the grooves that encircle the wheels while the cylinders
interface with the groves across the wheels. These links fit together using 1/16 inch
steel dowel pins. Originally, the links were narrower, but were widened for ascetics.
A full track is seen in the right image of Figure 16.
5.3 Battery Lid
The top to the battery compartment is also where the control board and Bluetooth
module are mounted. The Freaduino has a case but the lid can be kept off if the
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Figure 16: Left: Rendering of a single link Right: A full track of 34 links
user user prefers, though the lid is where the Bluetooth module goes. This side was
chosen to mount the control board on so that batteries beneath could be used as a
counterweight to the arm. The lid with the lid can be seen in Figure 17. The recesses
in the sides of the lid are to allow for wires to pass from inside the chassis to the top
so they can be plugged into the Freaduino. The Freaduino lid is one of the few parts
that actually requires support material while printing.
Figure 17: Rendering of the battery lid subassembly
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5.4 Servo Lid
The servo lid acts as the base of the arm. Only the shoulder servo is mounted to
it, but it does serves multiple purposes. As mentioned before, the recess seen on the
top left of of it in Figure 18 holds the ultra sonic sensor in place. The other slot is to
leave a gap so that wires can pass from inside the servo compartment to the outside.
It also has a recessed area to mount an additional sensor such as a button.
Figure 18: Rendering of the servo lid subassembly
The screws used to mount the servo are a little longer than they need to be, but
to minimize the different types of hardware, they are the same type as used other
places on the robot.
5.5 Arm
The arm allows the AZIBOt to manipulate the world around it. The gripper is con-
trolled by the gripper servo turning the drive linkage. The drive linkage is geared to
the other side. Each side of the jaw moves using a four bar linkage. By keeping oppo-
site links equal in length, the jaws stay parallel to each other. The arm subassembly
can be seen in Figure 19.
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Figure 19: Rendering of the arm subassembly
The upper part of the arm needed to be redesigned a couple times to make
inserting the servo easier. A better way to connect the arm pieces to the servo was
needed as a press fit would start to slip quickly. Glue was initially considered and
used on the first three prototypes, but a less permanent solution was needed in case
parts need to be replaced. The solution is to model in a recess that a servo horn
can fit into. Servo horns are meant to interface with servos and not slip. The drive
linkage for the jaw may be too small to fit a servo horn on, so an alternative may
need to be found. One potential solution is to not have the hole for the servo nob
be a through hole but have a cap on it with a smaller hole so that the piece can be
screwed into the servo.
5.6 Full Assembly
All of the subassemblies come together to form the full robot seen in Figure 20. The
battery and servo compartment lids are each held in place by four sheet metal screws.
These screws are the third and last type of screw used on the AZIBOt. The tracks
simply wrap around the wheels and are held in place by a final dowel pin. At this
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point, all that is left for the students to do is attach all the wires.
Figure 20: Rendering of the fully assembled robot
6 Future Work
There are still facets of the AZIBOt project that can be improved upon. Below is a
list of potential areas for further development:
1. As mentioned in the arm subassembly section, the connections to the servos
need to be made more reliable.
2. The robot is mechanically set up to host a Bluetooth module, but I was never
able to get the modules to communicate with anything. By adding Bluetooth
capabilities, it opens up possibilities for the end users including remote control
through phones or having AZIBOts talk to eachother.
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3. Further lessons can be developed to teach more advanced topics like inverse
kinematics. These lessons only require the knowledge of basic matrix multipli-
cation and can be used. This would allow the user to select a spot in space and
have the AZIBOt calculate what angles it needs to move the arm to to achieve
this position.
4. Accessories could be developed to add further functionality to the robot, such
accessories may include:
• A flat plate could be developed to replace the arm base. This could be
used as a base for students to develop their own modules on.
• Add other sensors to be used with the robot so the students can detect
other parts of the world around them.
• A sumo wedge to replace the arm that attaches to the shoulder servo.
This would allow the students to hold sumobot style competitions.
5. Currently the two driven links in the gripper are slightly different. With a
slight redesign of the tooth placement on the gears, they should be able to be
made identical, simplifying assembly.
6. The software used to program the AZIBOt should be able to run on most basic
computers. This software could be tested on Raspberry Pi computers. If it
works, then Raspberry Pis could potentially be supplied with some AZIBOts to
eliminate the need for a computer. The main hurdle with this is that Raspberry
Pis still require a screen, keyboard, mouse, and power supply. Keyboards, mice,
and power supplies are relatively cheap, but monitors are not.
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7 Conclusion
The goal was to produce a robot that could be used for education that was modular
and accessible. Though it is not as cheap as some of the alternatives, at a unit cost of
around $100 USD, the AZIBOt is still cheaper than some of its competitors such as
the mBot. The ability to 3D print the robot makes parts accessible anywhere there
is a 3D printer and allows for parts to be modified if the user desires. The ability
to use the parts in other projects along with the option to expand the capabilities
allows the students to grow as their skill grows.
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8 Appendix
8.1 Bill Of Materials
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References
[1] SenEcole - Inspiring Future African Engineers and Scientists. Retrieved
November 29, 2015 from Nano & Micro Systems Research Laboratory.
http://nmrl.unl.edu/index.php/outreach/senecole
[2] An All-African Robotics Competition. Retrieved November 29, 2015 from PARC.
www.parcrobotics.org
[3] Internet Usage Statistics for Africa. Retrieved November 30, 2015 from Internet
World Stats. www.internetworldstats.com/stats1.htm#africa
[4] mBot -STEM Educational Robot Kit for Kids. Retrieved November 30, 2015
from Makeblock. www.makeblock.cc/mbot/
[5] African Project Aims To Innovate in Educational Robotics. Retrieved November
30, 2015 from IEEE Spectrum. spectrum.ieee.org/automation/robotics/robotics-
hardware/african-robotics-network
[6] MIT Printable Robot. Retrieved November 30, 2015 from MIT Printable Robot.
sites.google.com/site/mitprintablerobots/
[7] AERobot: and Affordable Education Robot. Retrieved Novem-
ber 30, 2015 from AERobot: an Affordable Education Robot.
sites.google.com/affordableeducationrobot/
[8] Sparki - The Easy Robot for Everyone. Retrieved November 30, 2015 from Ar-
cBotics. arcbotics.com/products/sparki
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[9] Romeo BLE (Arduino Compatible Atmega 328). Retrieved December 1, 2015
from DFRobot. www.dfrobot.com
[10] SB-GVS Sensor Shield for Arduino Kit. Retrieved December 1, 2015 from So-
larbotics. solarbotics.com/product/39230/
[11] Base Shield V2. Retrieved December 1, 2015 from Seeed Studio.
seeedstudio.com/depot/Base-Shield-V2-p-1378.html
[12] A review about freaduino. Retrieved December 1, 2015 from ElecFreaks. elecf-
reaks.com/5661.html
[13] SpringRC SM-S4303R Continuous Rotation Servo. Retrieved December 1, 2015
from Pololu. www.pololu.com/product/1248
[14] Octopus Hunt Sensor. Retrieved December 1, 2015 from ElecFreak.
www.elecfreaks.com/estore/octopus-hunt-sensor.html
[15] Octopus Digital PushButton Brick OBPushButton. Retrieved December 1,
2015 from ElecFreak. www.elecfreaks.com/estore/octopus-digital-pushbutton-
brick-obpushbutton.html
[16] HC-SR04 Ultrasonic Sensor Distance Measuring Module Ultra01+. Retrieved
December 1, 2015 from ElecFreak. http://www.elecfreaks.com/estore/hc-sr04-
ultrasonic-sensor-distance-measuring-module-ultra01.html
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