Engineering Studies Dean Bothwell

2AB

Line-Following Buggy 2A Engineering Studies Dean Bothwell

Design Problem:

Manufacture a semi-autonomous skid steered buggy. This will be able to follow a black line on the floor using a triple infrared array. It should be powered by no more than 9V. The buggy will be controlled by a Picaxe 20M2 chip and the motors must be controlled through a solid state H-Bridge interface with the 20M2 chip. These motors cannot exceed 6V. The maximum voltage for the pickaxe chip is 5V, voltage differentiation must be used. The chassis footprint must be smaller than an A4 sheet of paper. The chassis must be made of 3mm acrylic and not exceed 1.5 kg operating weight. Allowances must be made for a possible upgrade to wireless remote control in the future.

ENGINEERING STUDIES 2A

Task2- Investigating Materials and Components

Materials; Comparison of suitable materials for chassis

*Priced at http://www.accentframing.com.au/glass-to-frame/products-and-pricelist #Linear metre

Components;

A line detector will be needed to track the line, this will require three LEDs coupled with three phototransistors, the line is detected by measuring the contrast on the floor. The LEDs emit light onto the surface and the phototransistors gauge the volume of light reflected. The black line will not reflect any light while the contrasting floor will. This fact allows the buggy to read the location of the line. A chip will be necessary to process the information collected by the line-following module. A PICAXE be used for its low cost and ease of programming. PICAXE supply various chip sizes, models come with the number of pins ranging from 8 to 40. The PICAXE micro-controllers can be reprogrammed while fitted into the circuit via a three wire download cable connection.

Material Durability Conductivity Weight(kg/m3) Cost($/m2)

Acrylic (3mm)

high shock, abrasion and flex

resistance

non-conductive 1,190 118*

Aluminium (3mm)

Long lasting and rust resistant

conductive 2,720 200-300

Wood (Untreated Pine)

no resistance to moisture,

easily damaged

non-conductive 500 7.73 (lin m#) (290x19mm)

The processor chip will alone not be capable to run the motors and make the buggy move, another component is needed to drive the two motors. There are two main choices of motor-controllers, the L293D and the L298;

Motors will be needed in order for the buggy to move. This motor will need to be able to rotate in both direction as the buggy will be relying on skid-steer technology to turn.

The PICAXE chip runs on 5V but the battery supplies 6V to the circuit, this means resistors will be needed to form a voltage divider to drop the supply to the required voltage.

Vcc = V1 + V2 Vcc is the total voltage

V1 = Vcc x R1/R1+R2 V1 is the voltage across resistor R1

V2 = Vcc x R2/R1+R2 V2 is the voltage across resistor R2

L293D L298N

All information taken from data-sheets published by

SGS-THOMSON microelectronics

http://www.st.com/web/en/resource/technical/document/datasheet/CD00000240.pdf

and http://www.ti.com/lit/ds/

symlink/l293.pdf

(unless *)

Min. Supply(V) 4.5 2.5

Max. Supply(V) 36 46

PowerDip Footprint(mm)

24.8 x 22.86 11.1 x 16

Difficulty of Fitting* Easy Hard

Difficulty of Programming* Easy Hard

!!

Mechanical;

The buggy as mentioned above will propelled and turned by means of skid-steer technology. These involves rotation of the wheels being in sync in order to travel forward or in reverse, and in opposite direction to turn left or right. To make my personal project dissimilar to my classmates I intend to fit three wheels onto my buggy rather to the two my classmates envision to have. The PCB is to be of each students own design, to set mine apart I plan to engrave my name into mine as a method of identification.

Programming;

The sole purpose of the project is to follow a black line on a contrasting floor. The buggy will do this using a triple array line-following module. This employs three pairs of LEDs and photo-transistors. Secured together in a straight line, they will detect where the line is by which pairs are on or off. The centre pair will be off as the transistor will not sense any light as there will be no reflection from the black line. The outer pairs will remain on until one passes over the line, once this occurs the 20M2 will register there is a need for a change in direction and it will relay this to the motor controller which will govern which direction the motors will rotate in in order to stay tracking the line.

The PICAXE processor chip can be programmed in BASIC(which is much simpler to learn than assembler code or ‘C’) or even through the use of flowcharts. H-Bridge circuits are the most common method of driving bidirectional motors. This is because the direction can be changed by changing the direction of the charge.Running the charge from left to right makes the motor turn clockwise while running it from right to left makes it turn counterclockwise.

Task3- Devising a Solution

Materials; The design problem limits the material choice for the chassis to 3mm acrylic. This material was chosen for it’s availability for our class. Other materials could be chosen but acrylic is the most appropriate. It has the durability of the aluminium but does not conduct electricity so it allows the PCB to be attached without the danger of influencing it. It is more attractive and easily machined than wood. It can also be machined in the CNC machine present in our classroom. These characteristics make it a good choice in material for the buggy chassis.

Components;

A line detecter; This module will detect the whereabouts of the black line the buggy is following. It will consist of a PCB fitted with three LEDs coupled with three phototransistors working to track the black line. The layout will be designed by the teacher and all students will have the same design. This module will be fitted at the front of the chassis and close to the ground to accurately track the line.

20M2 Picaxe processor; This component will be fitted onto the PCB attached onto the chassis. It reads the information the line detecter provides, interprets what action is needed continue following the line and then sends the instructions to the L293D Motor Controller which will then act accordingly. The 20M2 chip has 20 pins allowing space to enable upgrading the buggy to remote control in the future.

L293D Motor Controller; As the 20M2 chip does not have the power to run the two motors a motor controller chip must be inserted in order to drive the buggy. We are using the L293D as it is easier to accommodate on the Printed Circuit Board than the L298.

Motor and Gearbox; We have been issued modules that contain both the motor and gears inside, by the teacher chosen for its availability. Each student needs to consider this component when designing their chassis.

Resistors; Some components run on lower voltage on others. As a result of this resistors in a voltage divider arrangement will be used to drop the voltage to the appropriate value.

Vcc = V1 + V2 Vcc is the total voltage

V1 = Vcc x R1/R1+R2 V1 is the voltage across resistor R1

V2 = Vcc x R2/R1+R2 V2 is the voltage across resistor R2

Capacitors; These act as shock absorbers that suppress the ‘noise’ given off by the motors and protect the chip from it.

Mechanical;

Wheels; The buggy will be driven by two wheels mounted at the front section of the chassis. My design allows for a wheel diameter of 50mm.

PCB; The Printed Circuit Board will carry the electrical components in a circuit. It will hold the picaxe processor chip, the L293D Motor Controller, the resistors needed to drop the voltage, capacitors that act as shock absorbers that suppress the ‘noise’ given off by the motors and the wires that carry the charge. This component is to be of my own design and cut out on the CNC machine. To make my PCB unique to me, I am having my initials engraved on the board.

Chassis; The chassis will consist of a main base plate, in a shape similar to a shovel head, two ‘walls’ will hold the motors in place and a roof that will bridge the two walls. The roof will also be used for identification purposes further setting my project apart from my peers. All elements of the chassis will be made from 3mm acrylic as instructed in the design problem. The design problem restricts the chassis footprint to less than that of an A4 sheet of paper(210mm x 297mm), but the smaller the footprint the less material is needed reducing cost and cutting time of the material.

Slider; This element is a small piece of plastic that takes the place of a trundle wheel that I originally intended to have. I decided to use this instead after being shown the advantages of the slider over the wheel. These being the reduced size of the whole machine as well as it being cheaper and easy to manufacture.

Battery; The buggy will be powered by four AA batteries supplying 6V to the PCB and giving power to all the electrical components.

Programming;

The sole purpose of the project is to follow a black line on a contrasting floor. The buggy will do this using a triple array line-following module. This employs three pairs of LEDs and photo-transistors. Secured together in a straight line, they will detect where the line is by which pairs are on or off. The centre pair will be off as the transistor will not sense any light as there will be no reflection from the black line. The outer pairs will remain on until one passes over the line, once this occurs the 20M2 will register there is a need for a change in direction and it will relay this to the motor controller which will govern which direction the motors will rotate in in order to stay tracking the line.

The L293D; This chip has a h-bridge integrated into it’s circuit. This allows it the change the rotation of the wheels by changing the direction in which the charge flows through the motor as shown in the diagram.

Running the charge from left to right makes the motor turn clockwise while running it from right to left makes it turn counterclockwise.

Solar Tracker 2B Engineering Studies Dean Bothwell

Design Problem:

Research, design and manufacture a solar tracker. This will employ a feedback unit to read the position of the panel, independent of the sun sensors. The unit will have a dusk reset function built into it. The project will be powered by no more than 6V. The tracker can use anywhere from 3 to 5 Light Dependent Resistors. The base of the tracker should be no larger than the size of A5 paper. The chassis is to made of 3mm acrylic. All parts are to be designed and constructed by student. Justification of design concepts is required for gaining marks.

ENGINEERING STUDIES 2B

Design Brief

I am going to investigate and design a stationary system that will find the position of the sun and move in order that the panel will be exposed to the greatest amount of sunlight possible. This system integrated with photovoltaic cells can be applied in many types of industries ranging from household electrics, to driving pump operations on a farm or site. I will be manufacturing a working model of the project. This model will have a base area of no larger than the area of an A5 piece of paper. The chassis will be constructed of acrylic due to ability of materials. The components will be driven using a 20M2 picaxe programmable chip. The position of the sun will be calculated using light dependent resistors(LDRs). I will use four LDRs, one for each bearing(one for North, another for South etcetera). The movement will be produced by servomechanisms(servos). The panel on the project, mimicking a solar panel, will rotate on two axes therefor two servos must be employed. One will be used to move the panel for changes in the sun’s position and the other for seasonal changes. A potentiometer will be used as a feedback unit reading the position of the panel, this info can then be used to read when the panel is at a certain position this me to program a dusk reset function, returning the panel to it’s initial position preparing it for the next day.

A circuit must also be designed. The printed circuit board(PCB) will contain the power component(a 6V battery pack), the chip(20M2) and download socket, as well as terminals providing power and information to the external components(the servos, potentiometer and the LDRs). The circuit and chassis of the circuit will all be designed by myself using research information on the possible way of making the systems components work in the desired way.

Task3- Investigating Materials and Components

Materials; Comparison of suitable materials for tracker chassis

*Price as found on https://www.blackwoods.com.au

Other materials are needed. What specific brands of components will be used will be chosen according to availability and supply cost.

Components;

Material Description Properties Cost($/sheet)*

Acrylic (3x1220x2440mm)

Thermoplastic polymer

Clear, lightweight, rigid and weather-

resistant

118.18

Aluminium (3x1200x2400mm)

Pure element or alloy

Lightweight, strong, malleable, machinable

and corrosion resistance

196.36

Brass (3x900x1800mm)

Alloy of copper and zinc

Strong, machinable, wear and corrosion

resistant

26.18

MDF (6x1200x2400mm)

Engineered wood product

N/A 27.59

Galvanised Steel (1.5x1220x2440mm)

Steel with protective zinc coating

Strong and corrosion resistant

130.91

Component Parts

Measuring • Light Dependent Resistors • Potentiometer

Movement • Servomechanisms

Structure (Chassis)

• Base • A-frame • Panel • Printed Circuit Board

Electronic • 6V Battery Pack • 20M2 Picaxe Chip • Wire • Resistors • Download Socket

Another factor affecting the cost is the amount of material used. The amount will depend on the chassis design I decide to use.

Existing Solar Tracker Designs Design Description Postive Negative

Simple wooden design with tilting

panel in a panning frame atop a wooden

box pedestal

• Simple design • Electronic components stored in

base.

•Not very aesthetically pleasing

Multiple panels, day tracking occurs as

panels tilt, seasonal change occurs

through rotation of frames axle

• Aesthetic appeal • Multiple panels

tracking at once

• Large footprint • Lots of material used

in construction of chassis

Heavy mechanical components with pan and tilt using multiple

gear mechanisms employed for

movement

• Heavy Duty • Strong Structural

component

• Complex mechanical component may make

servicing difficult

Tracking in this design is the rotation of the panel on a diagonal

axis.

• One moving part servicing will be easier • Support can be

replaced by existing wall

• Seasonal changes seem to be changed

manually or are nonexistent

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Mechanical;

The tracker will employ a pan and tilt mechanism to follow the sun through the sky. In my model two servos will be implemented each rooting a different axis. The method the servo uses can vary. Some ways of moving the panel and frame are;

• Levers • Linkages • Gears • Chain and Belt Drivers • Worm Drives

-Levers One method of changing the position of the panel is fitting the servomechanism straight onto the A-frame or panel with the servo’s arm attached to the adjacent piece of frame work. This class 1 lever uses the high point of the structural frame as the fulcrum or pivot point. As a result of its simplicity this method means operation is easier as well as reducing the difficulty of maintenance.

-Linkages This method is similar to the lever method but instead of attaching the servo straight onto the panel the servo is linked to it via a linkage mechanism. The movement is carried through linking arms turning the rotational motion of the servomechanism’s motor to linear movement. This allows us to change the angle of the panel by a push and pull action.

-Gears Gears sometimes known as cogs can be useful in many applications. These wheels with teeth that mesh together can be used to transmit torque or speed depending on the ratio between the gears. Applying gears to this model solar tracker an arrangement could be employed to attach the servos turning to a potentiometer which then can be used to measure the position of the frame.

-Chain and Belt Drivers This is a gear arrangement where instead of the cogwheels being in contact with each other the movement carried through a chain or belt. The application of this in the project is the same as the gears above but the chain will allow the distance between the servo and the potentiometer to be greater without needing multiple gears in sequence.

-Worm Drives A worm drive is a gear arrangement where a gear turns causing a screw to revolve. This arrangement can find application in the project as a method of again turning the horizontal rotational motion of the gear to the vertical rotational motion of the worm or thread on a perpendicular shaft,, this allows the servo to rotate a vertical shaft without having to support the weight of the frame above. This method however is complex as operation implies a lot of calculations as the main function of worm drives is speed reduction and amplification of torque which is not a requirement in the design and operation of a solar tracker.

Programming;

The tracker will use the light reading from the light dependent resistors on the panel to inform the chip how much light the panel is being exposed to at any given time and will adjust so that the panel is the panel is in the optimum position and will be exposed to the greatest amount of exposure possible. For this to occur the micro-controller must be programmed to operate and conduct the measurements and then decide what action is to be taken. All project will be by myself using Picaxe Programming Editor. I will write a code that will run all functions in the appropriate manner so that the tracker may operate effectively. Such functions include;

• Reading light levels of East and West LDRs • Reading light levels of North and South LDRs • Reading position of panel • Reading position of framework • Adjusting panel position and angle for optimum exposure • Reading position of frame so the project is able to reset for the following day

Using the LDRs in a voltage divider arrangement I can use the signal reading from between them to find the position of a light source. This cuts the need for additional resistors on the PCB allowing it to be smaller. Once the potentiometers in the servos reach a certain value the unit will return to it’s initial position, this will be called Dusk Reset.

On the Picaxe 20M2 chip there a number of ADC inputs and outputs. For the LDRs I will use the left side this allows me four possible pins to chose from these being; C.7 and C.1 through to C.3. On the right side for the servos I can chose anywhere from B.0 to B.6.

Task4- Developing a Solution

To answer the design problem and to satisfy the design brief, I am going to design a solar tracking unit that will satisfy the criteria that is demanded. My design will feature a chassis made of 3mm acrylic due to the availability of the material. The whole unit will be powered by a 6V battery pack. it will employ four light dependent resisters to find the position of the sun and then two servomechanisms will adjust the position as to expose the ‘solar panel’ to the most light possible. I have researched existing designs of solar trackers and have brought some design traits to bear on my own.

I have produced annotated concept drawings and from these decided on a final design which I have produced drawings on AutoCAD. The devising task of this project also involved producing justification of my design choices, a list of the materials required in constructing the unit and the approximate costing of the project and its materials.

I have also been tasked with the producing the PCB which will hold all the electronic components, for this I have been tasked with creating a circuit diagram and convert this to a PCB layout. I will produce these on CircuitWizard and PCB Design and Make. The PCB will contain a 20M2 Picaxe chip this runs on 5v whereas the servos run on 6v this means a voltage divider must be used to vary the voltage value. This can be done using 1K and 5K resistors in a voltage bridge arrangement to drop the voltage so the chip and servos can run in the same circuit. My design uses the interior potentiometer inside the servos to calculate the distance so an extra potentiometer is not necessary.

The chip will also need to be programmed. The codes will be written by me using Picaxe Program Editor. The code needs to make the unit move and function efficiently. The time frame for this project is the entirety of Term 3, with different assignments making up the final portfolio. These are;

• Task1- Design Brief (Week 1-2) • Task3- Investigating materials and components to develop a solution (Week 2-3) • Task4- Developing a solution (Week 4) • Task5- Pre-production (Week 4) • Task6- Manufacturing (Week 5-7) • Task7- Evaluation of completed project (Week 8)

Examples of my design process for developing a solution to the design problem are as follows.

• Concept Drawings • Circuit Diagram • PCB Layout • CAD Drawings • Parts and Materials List • Programme codes

Concept Drawings

All concept sketches produced by Dean Bothwell

Drawing Description Positve Negative

“Saddle”

Two A-frames combine to create a gimbal in order to

produce the movement servos are

attached as the fulcrum

• Unique design

• Less moving parts

• Not aesthetically appealing

“See-saw”

The panel is balanced on an A-frame, the

frame is then mounted on a rotating base

• Simple mechanism

• Less usage of material than

Concept1

• Similar design to real life solar panels

• Not as unique as Concept1

• Does not show any signs of intuition

“Birdhouse”

In this concept the daytime servo rotates the frame and a gear the gear intern turns a potentiometer which then measures the

position of the frame

• Gear arrangement show thought was put

into designing

• Still reasonably simple mechanic

involved

• Multiple moving parts, gears able to

become clogged with dirt

“Push & Pull”

This frame is mounted onto a rotating base,

seasonal tilt is managed by a

pushrod fixed to the underside of the panel

• Pushrod arrangement implies

high standard of engineering in

design

• Similar concept to industry linear driven

solar trackers

• High standard of mathematical

calculating involved

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Circuit Diagram

Printed Circuit Board

Computer Aided Drawings(CAD)

Parts and Materials list

*Cost of 1220 x 2440 as standard commercial sheet size ** Cost of 16m smallest available quantity of wire, Most prices found at http://www.jaycar.com.au

Component Part Code/Material

Quantity Cost/Unit Cost/Total

Chassis

Panel 3mm Acrylic —- —- —-

Frame 3mm Acrylic —- —- —-

Base 3mm Acrylic —- —- —-

Total 3mm Acrylic 500 x 400 $118 $118*

PCB

Resistor(330) RR2762 2 $0.48 $0.96

Resistor(1K) RR2774 1 $0.48 $0.48

Resistor(5K) N/A 1 $0.55 $0.55

Resistor(10K) RR2798 1 $0.48 $0.48

Resistor(22K) RR2806 1 $0.48 $0.48

Chip(20M2) ZZ8700 1 $4.70 $4.70

6V Battery Pack

PH9209 1 $1.95 $1.95

Wire WH3025 1 $4.95 $4.95**

LDR RD3480 4 $3.25 $13

Servo HXT500(5GR) 2 $3.41 $6.82

Total $34.37

Project Total $152.37

Programming;

The programming was also to be written by myself. This was to be done using Picaxe Programming Editor. Since I am only a novice in this section of the project I requested aid from the lecturer and classmates. We started by focusing on small segments of the coding. Examples of which are;

The use of servos;

main: servo 0,180 pause 500 for b0 = 80 to 180 servopos b. 0, b0 pause 200 next b0

goto main

The use of potentiometer in changing the position of a servo; main: servo 0 , 180

drive: readadc B. 5 , b5 let B0 = b5 / 2 + 75

pause 10 servopos 0, B0

goto drive

The use of reading light level using LDRs;

main: readadc C. 1, b1 readadc C. 2, b2 pause 100 debug

goto main

From what I learn from these small segments I hope to be able to write one complete code which will instruct the unit how to operate as it should.

Task5- Production Procedure

After creating a design brief from the provided design problem we could go about conducting research on existing means of tracking the sun. Once we had finished investigating current methods we were able to begin developing our own project. The developing stage consisted of concept sketches and basic coding. Once a solution to the design brief was completed and plans drafted the materials and components needed for manufacturing the tracker could be acquired. The CAD drawings of the tracker chassis were then inputed into the laser cutter. These could then be fastened together using superglue to bond the pieces to one another. The PCB, as it is made of a different material needed to be cut on the CNC machine. Once all components were acquired they could be assembled and the board populated with the electronic components. Once the electronics were in order the programming could be started. Once the code had been written and tested it could be downloaded into the micro-controller. Once assembled the project could be tested as a whole unit, any improvements needed are the made until the project is functional and provides satisfactory results.

DISTRIBUTION OF TIME TO TASKS

Week

0 1 2 3 4 5 6 7

Design Brief Research Developing Solution Pre-production Manufacturing

TIME SPENT ON PRACTICAL ASPECT

Programming

Assembling

CAD

TIME SPENT ON WRITTEN ASPECT

Developing

Research

Design Brief

Assembly Instructions

Task7- Evaluation

I decided to design my panel and chassis in the shape of an octagon for plagiarism reasons. Too many people copied my original idea of a circular base and rectangular panel. I switched to an octagon to make mine different to the other students. I also cut a ’N’, ’S’, ‘W’ and ‘E’ into the walls of the chassis, this show the poles to which the panel would be orientated. A further difference in my design is the inclusion of my initials cut into the side frames holding the panel in place. I also set my project further apart from the others by fixing the LDRs to the frames sides rather can top the panel as the others have done. This means my LDRs shade does not come in a cross or ‘x’ layout, instead its a simple divider between the two seasonal light change detectors.

One thing most of the projects have in common is a hole cut to allow the wires from the LDRs and top servo to drop thru to the PCB. I designed an ‘arrow’ so that the panels position may be changed via a paper clip or other link between it and the servo arm. For this to work the servo had to be fixed in a position that the arm would be parallel to the panel. For this to happen I manufactured a bracket to hold it in a position that the whole unit would function properly. All parts, once cut out, are held together with loctite. The pieces fit together using mortises and tenon like fixtures. Small tags on pieces fit into slots in others.

The design brief required the project to be made of acrylic but MDF can be appropriate to use. The project existed the time allotted with programming been done after the time set aside for it. With the laser cutter being used in production the project could be mass produced. The project is safe to use and the only safety hazards may be in the manufacturing of the product as soldering of the PCB can cause burns and inhalation of the fumes can cause lung problems. Other lung problems can be inhalation of acrylic dust and inhalation of superglue may cause damage to the brain if exposure is prolonged.

The design brief insisted on the project fitting onto an A5 piece of paper, my project fulfils this constriction. The project is set to work when the programming is downloaded, but with all projects there are problems. My project was no exception. There was a problem with measurements and flaws in the design of the chassis and in the Printed Circuit Board. Problems I encountered were;

• Three rings were too big so one had to be removed • There was a short in the circuit board • Gluing my project ended with me in a sticky situation • The circuit had to be designed and redesigned many time