accelerometer controller robot

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Nathan Raj 2

Table of Contents

01) Cover 0) How an ADC works 39) Circuit I/O tables 58) Car Programming V3

02)Tables of Content 21) Practical Investigation 2 40) Laser Cutting 59) Dual Core System

03) Project Overview 22) Mathematical Analysis 41) Potential Designs 60) New Program Algorithm

04) Needs and Specification 23) Practical Investigation 3 42) Prototype Development of Controller 61) Explaining how improvements work

05) General Discussion 24) Questionnaire 43) Potential Designs 62) Single Core Vs. Dual Core

06) Spider Diagram 25) Questionnaire Results 44) Prototype Development of Car 63) Correcting Differential Torque

07) Possible Control Systems 26) How to make a PCB 45) 2D Design Files sent to Laser Cutter 64) Reprogramming the OLED

08) Planning my research 27) Controller Circuit Board Breakdown 46) Controller I/O test 65) Hardware Improvements

09) Existing Products 28) Controller PCB Breakdown 47) Car I/O test 66) Injection Moulding methodology

10) Background Research 29) Controller Breadboard 48) Program Algorithm 67) PCB Production in Industry

11) Hand sensor Research 30) Car Circuit Board Breakdown 49) Controller Programming – Problem 68) Design for Market

12) Control Processor Research 31) Car PCB Development Breakdown 50) Controller Programming V2 69) Future Communication Improvements

13) Wireless Communication Research 32) Car Breadboard 51) Car Programming V2 70) Cost14) Screen Research 33) Explanation of Circuits 52) Photos showing the controller working 71) Time Gantt Chart

15) Quality Testing 34) Comparing Car Circuit to PCB 53) Final Design 72) Specification Evaluation

16) Types of Motors 35) Comparing Controller Circuit to PCB 54) Problems 73) Health and Safety and the Environment

17) Possible Motor Control Circuits 36) Comparing Controller PCB Design to Auto-router 55) Improvements 74) SWOT

18) Motor Power Delivery 37) Comparing Car PCB to Design to Auto-router 56) Two Way Handshake Routine 75) Gallery Page 119) Practical Investigation 38) Front and Back View of PCB 57) Controller Programming V3 76) Gallery Page 2 and Final Client Comments

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Project Overview - for Examiner use

Practical Investigation

Built arm mounted Controller

Built Robot with ultrasound

Handshaking Corrected differential torque

Pages 17-21 Pages 26-28, 37-39, 40-41, 45, 47-49, 51-52

Pages 29-31, 37-38, 42-44, 46-47, 50, 52

Pages 55-57

Page 62

I conducted a practical investigation into the workings of the accelerometer. I learned how to interface with the device using a PIC chip’s ADC.

I designed most aspects of the controller including the PCB, case and the programming.

I designed most aspects of the car including the PCB, case and the programming.

I created a lock mechanism which only allow the car to be controlled after the correct code has been submitted to it.

I corrected the slight difference in power output between the motors. This reduced the effect by a factor of twenty..

Built a Dual core SystemPages 58-61

I designed a new robot which had a second chip which communicated via the use of hardware interrupts

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Needs and Specification

Needs SpecificationProblem and brief:There is no problem to resolve. I am trying to create a game for people to enjoy. The enjoyment will help release endorphins into the blood which will relieve stress in the users. It will also improve hand-eye coordination and stimulate an interest into high-tech toys.

User Requirements: Car should travel at a minimum of 0.1ms-1

Batteries must last one hour Easy to replace batteries The OLED must be visible to read from the screen at 50cm. The R/F units must be capable of working at 15 meters The car must be able to go forwards, backwards, and

rotating about a point so it turns within its own length There should be no noticeable input lag from the

controller The vehicle will have streamlined and appealing form The LEDs must be visible at 2 meters. It must be capable of crossing different surfaces The accelerometer must intuitively allow control over the

car Ultrasound can reliable detect walls at 30cm Must be able to run over a variety of domestic materials. The controller must contour to fit the forearm. The car must be small enough to use in a domestic

environment

Target Market:My Product is primarily for people who are interested in racing or cars. However, as it is also entertaining as a toy in its self so its target audience can be extended to a wider range of anyone above the age of 5. My client is my 13 year old brother who is studying towards his GCSEs

Scale of Production: This will be a one off prototype

Cost: I aim for the cost to be under £250. Costing of prototypes is a complex area - please see discussion later.

I love all of these ideas but can you make it look like a UFO?

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What is the need or problem I can solve?There is no problem to resolve. I am creating a for people to enjoy and relieve stress and perhaps stimulate an interest in technology.Who are the potential users?Everyone who enjoys RC vehicles, hopefully it will appeal across all ranges – ‘fun for the whole family’.How can I solve the problem?There is no problem to solve other than designing a novel RC vehicle which could possibly find a profitable niche in the market.What benefit will it bring to the users?A high quality R/C car that works anywhere, anytimeWhat might the intended product be?A R/C Car which is controlled by an arm-mounted accelerometerWhere would the product be used?Anywhere where there is space, I would imagine largely inside a ‘normal’ domestic space.Does it conform to a specific size?It has to be small enough to exist in a domestic environment.Does it have to fit any regulation or safety quality?There will be no small removable parts that can be swallowed by small children. It will be a low voltage/current system.What about aesthetics?It should look appealing to adults and children.What kind of material and processes can I use?I will use a laser-cut plastic sheet for the case and etched PCB for the circuit board.How should the product perform?It should be fast enough and manoeuvrable so that it is fun to use. It must also be tough enough to withstand crashing into objectsWhat is the potential price range?£150-250Is it something I can design and make?I have completed a GCSE in Electronic Products and the AS systems exam. This has provided me with the necessary skills operate 2D design for the Laser Cutter and the programming skills to uses PICAXE programming Editor using PICAXE BASIC and to use PCB wizard to design a compact circuit board. Google sketchup will assist with 3D design.

General Discussion

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Spider Diagram of Possible Options

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Possible Control Systems

All of my options are based on the PIC process stage. PIC chips can handle lots of inputs and outputs and drive several outputs like sounders, OLED. PIC chips are highly capable because of their large memory and their ability to handle large complex programs. I decided that all of my proposed ideas will use accelerometers are input devices as way of easily comparing the results

Possible inputs Processes Possible OutputsIdea 1 Wired Controller PIC chip OLED,LEDs and Motors

Idea 2 IR LED on the controller and IR Detector on car PIC chip OLED,LEDs and Motors

Idea 3 XBee R/F Pro Chip on both car and controller PIC chip OLED,LEDs and Motors

Chosen Idea XBee R/F Pro Chip on both car and controller PIC chip OLED,LEDs and Motors

I did not choose Idea 1 as the wire would be a serious trip hazard if it was long enough to allow free movement. There is always the danger that it could be ripped out of the controller / vehicle causing damage.I chose against Idea 2 because while it offered wireless function, it could not function without direct line of sight which would be useless on controller which requires user to rotate it (to activate the accelerometer steering) potentially out of sight!I chose Idea 3 as it offered both a wireless feature and does not require line of sight meaning it is the only suitable communication technology beside more expensive implementations like Wi-Fi and Bluetooth. The only potential problem might be interference from other 2.4GHz systems. I will use qualifiers to help prevent this – see coding notes.

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Planning my research

Primary Research

Practical Investigation Here I test the accelerometer to test its suitability as a control input for the controller. I will use various tests and mathematics to measure and calculate the response from the accelerometer.

Potential Components I compare several different components to judge which will be suitable to use for as the sensor, processor, wireless communication and a screen for input feedback.

Questionnaire I will create a questionnaire for my target audience so that I can get their opinions about the product and see their reactions to different potential features.

Clientele Discussion I will meet with my target audience/client and have a general discussion about the features that they would like to see in my product. Client input is necessary to ensure that they will be satisfied with the end product.

Secondary Research

Target Audience My product is an electronic toy car with a novel input so it is aimed at children., with hopefully some appeal to the whole family.

Quality and Health and Safety Standards

I will consider whether my product has to meet any specialised standards for its purpose and ensure that it is not considered a health risk.

Existing Products I will research existing products. I expect that these will be found mostly either in market as toys or entertainment devices. These will be mainly RC vehicles. I doubt if a wide variety utilising my proposed inputs will be available, but I can look at RC vehicles in general to determine the types of control system and inputs/outputs available. I can get some idea of cost and what is currently selling in the market.

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Existing Products

HDD Fall Protection Sphero 2.0 Myo Ipad

HDD can come with accelerometer built in which detect when vibration or free fall is detected so that the heads can be unloaded to prevent a head crash which would be catastrophic for data on the drive.

The toys uses an accelerometer and a gyroscope for stabilising the ball as it drives around. This allows for very little effort on the user when driving as they only need to specify a direction and the robots will obey.

The Myo is armband which straps around your arm and allows you to use sensors to control UAVs and various devices. It uses 3-axis accelerometer, 3-axis gyroscope, 3-axis magnetometer and a EMG sensor to track the arm in 3 dimensions and when they are tensing the muscles to provide multiple trigger points for control devices.

The Ipad has a accelerometer built in which allows it to detect its orientation which allows the screen to rotate when watching a video. Also games can take advantages of the raw data as a alternative control methods for games so the user can tilt the device to drive cars and planes.

These products shows that accelerometers are becoming more commonplace in toys and there is a market for the product. I am particularly impressed with the speed of response needed by the first product. I need my vehicle to be responsive to real time movement of the arm, so hopefully this shows that this should not be a problem.

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Background Research – Phone accelerometer

The accelerometer is a form of a modified capacitor. As you can see in diagram (b)you have the two plates of a capacitor with a seismic mass in between the two plates acting as the dielectric. In electronics capacitance is proportional to the area of the plates, the distance between the plates and the distance between the dielectric and the plates. Inside a phones accelerometer each capacitor has the same sized plates and the same distance between the plates However, as the phones is moved around the seismic mass is shifted causing the dielectric to move around this causing the capacitance to vary.This change in capacitance is detected using a H-bridge arrangement of capacitance(c). The input signal is applied across all four capacitor and is a AC signal with a specific phase angle. As one of the capacitors change the output signal which is taken across the bridge changes its phase angle relative to the phase angle. It is then possible this phase change into a voltage change which can be feed into a ADC port of a PIC chip. There is three sets of these capacitors mounted perpendicular to each other allowing for the three axis to be measured simultaneously.

(C)

They have only relatively recently become sufficiently small and low cost enough for widespread use in hand held devices. They are sold with a specification quoting a sensitivity of output voltage per g. They are also available in 2 or 3 axis configurations.

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9DOF Razor IMU MMA7361L Flex Sensor

This IMU costs £46.59 and contains an accelerometer, a gyroscope and a magnetometer. This means that it will be overbuilt for my purposes. Also the accelerometer provides an output with a 13-bit resolution which the PIC chip cannot handle. This means I would have to look into alternate control processers to use this. The magnetometer and gyroscope look like they are intended for some kind of inertial guidance capability.

This accelerometer cost £9.84 and consists of a 1.5g accelerometer which measure pitch, roll and yaw in 8 bit resolution. The output from the 3 axis can be fed into the ADC pins on the PIC Chip and at certain thresholds the car will move in a certain direction. This makes its and accurate and effective control input for the car. It operates of the same voltage supple as the rest of the circuit.

The flex sensor sells for £4.93 and is very simple to program as it will feed an analogue voltage into the ADC pins on the PIC chip and the thresholds can be set to perform different tasks. However it will need to be incorporated into a potential divider, as flexing it alters its resistance and the potential divider translates this into a voltage change. It might also be difficult to incorporate into something to mount on your hand presumably it could be sown into some kind of gauntlet – but this all adds time and complexity.

Hand Sensor Component Research

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Arduino Mega 20X2 PIC Intel I7

This Arduino chip retails at £26.90 and uses C a programming languages that I do not currently know. However, any pin can set up for analogue or digital I/O. This means it can complete advanced multi input functions easily. It has a higher clock speed than the PIC and is more capable. However my lack of familiarity and the limited time frame available means it will probably be excluded.

This PIC Chips sells for £4.99. It uses a specialised form of BASIC which I have experience with. It is low current so it will not sap battery power but lacks some advanced features like ADC on all pins. All things considered it is an cheap and simple method for constructing a prototype. It supports interrupts for scanning and responding to inputs quickly.

This is a high speed multicore processer will sells for £219.99. This allow for far faster and more complex coding in a variety of programming languages Like Python which I am currently learning. However, it is extremely expensive as it also includes FPUs which I will not be using. This results in a product which is not cost effective. It is meant for controlling ‘computer’ with their complex interfaces and running an operating system.

Control Processer Component Research

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XBee Wi-Fi XBee® DigiMesh® 2.4 Infra-Red Emitter and Receiver

This is a high-end transmitter and receiver which operates with Wi-Fi protocol . It can be used with the same commands and it uses SSIDs as headers to reduce interference as the DigiMesh model will pick up all radio waves on the 2.4GHz band. However, it is primarily used for mass data transfer on a mesh network so is overbuilt for the specification.

This is high–end radio frequency transmitter and receiver. It easily be repurposed on the fly depending on the program needs. It requires a simple serout command in BASIC. Also the signal can travel through walls and upside down so it can be easily used alongside the accelerometer. This means that it is viable option to fulfil the specification.

This is a extremely simple method for line of sight communication . This hinders its benefits as it requires the user to bee able to point the emitter at the car at all time. This is not feasible due to the how the accelerometer will control movement. The accelerometer requires the user to rotate the device so line of sight can not be maintained. So this is an entirely inappropriate device. Data transfer rates are also lower than with Wi-Fi type systems.

Wireless Communication Component Research

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LCD Screen OLED Screen Graphic OLED Screen

This LCD screen at £4.61 is the cheapest option However, it uses a backlight which means it uses more battery power which will reduces the play time of the controller. Also the backlight does not provide as much contrast which could lead to eye strain for the consumer

This OLED screen retails at £14.37 so is more expensive but as it does not use a backlight is it provides a better contrast ratio and is more power efficient so the controller does not need to change battery as often. I have programming experience with this screen before as well. This is the product that I will go with.

This OLED screen costs £16.27 and so is the most expensive of the possible option. It offers the ability to display small graphics alongside the text. This means it is harder to program and given the time constraints this is not an option at this time but could be a future improvement.

Screen Component ResearchI only looked at 2 line displays as these have compact footprints suitable for fitting on a hand mounted unit. 2 lines should be adequate for a basic UI.

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Make PCB Visual Check

Write some code to test the outputs

Write Code to test inputs by getting them to

activate the outputs

Connect BatteryPower gets to the chip

and is tested with a multi-meter

Download empty program to check if the chip can talk

with a computer

Solder Gaps

Develop Code for Final Prototype

Re-solder

Re-solder

Re-solder

Re-solder

The reason for testing the outputs before the inputs is that if there is a failure then the problems remains undiagnosed.

Quality Testing

Made sure there were no cross tracks No overlapping components The above can be done at the design stage, after printing the mask onto acetate and

after printing the design onto a PCB UV light box – a pale yellow print should appear Develop the PCB while checking for broken tracks with a continuity test using a multi

meter Download a blank program to the chip Download test code to check inputs and outputs – test outputs them use them to test

inputs Develop program and test against specification

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Types of motor Description Picture Comments

Stepper Motor A motor that is programmed to move in steps used mainly in printers.

This motor is not useful as it only works in steps. This allows for accurate turning. However, I require fast continuous rotation which means that they are not helpful. They need a driver chip to interface between the PIC and motor.

Servo Motor A motor that accurately positions the motor to within 2700 for high precision tasks.

These motors are originally intended to turn 270 degrees, However, they can be modified by removing a plastic tab on the gears that stops it rotating to far and also removing the variable resistor that gives the control circuit the motors position. The inbuilt gearbox also gives a low RPM to achieve high torque. Again limited use in my project as I do not require turning anything to a specific angle.

DC Motor A shaft suspended within a magnetic field as power is fed to it, it spins at a high RPM

I decided to use this type of motor because it is best suited to the needs and specification to my project. It provides a larger amount of torque as well as having a variable RPM (using PWM) which enables me to have a fast and slow mode to my game. However, the only problem would be that they cost more which would reduce the profit margin on any sold. They are available in a wide range of input voltages, and have a variety of gear ratios using the attached compound gear box. They can be controlled using H bridge circuits – usually in a motor control chip like the L293d which enable 2 motors to be controlled using 4 outputs from the PIC.

Type of Motors

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Circuit 1

This first circuit uses a variable resistor to speed up and down the motor. The variable resistor However, takes a lot of current which reduce the RPM of the motor at the expense of heat and there is no direction control. Also it relies on the user to move a switch on the car itself which fails the specification point of being 15 metres away

Circuit 2

I can use the pins C.3, C.4, C.5 and B.4 to utilise the hardware PWM built into the 20X2 chips to control a motor. However, I will need two PIC chips one for each motor which is a waste of space and resources. I can synthesise PWM by using the high low and pause commands – see later coding.

Circuit 3

I could also use a H-bridge circuit and this can be controlled by a PIC chip. The FETs can handle the large currents required to turn a motor at the RPM I require for the car. By activating the FET alternatively the polarity across the magnets in the motor can be reversed allowing both backwards and forward motion and by applying PWM from the any of the pins unlike the last circuit the last circuit to the top FET of each activated pair I could get speed control. However, I will need two PIC chips one for each motor which is the same issue as the last design

Circuit 4This IC is the L293D chip which has 2 H-bridges built into to control 2 motors so resolves the issue of needing two PIC chips. Its inbuilt logic allows 2 lines to control each motor rather than the 4 required if the PIC and H bridge were directly connected. It needs a 5V supply for this as well as a separate higher voltage/current supply for the motors. The motors can produce voltage spikes on the power lines degrading the performance of the PIC – so separate power is good. All power supplies are connected to the same 0V line as this is the reference voltage which the PIC/L293d uses to determine what is a high/low signal.

Possible motor control circuits

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Motor Power Delivery

Common Negative

Motor Specific Power Supply

Control LinesPIC Chip

PCB power Supply

Motor 1

Motor 2

As you can see in the above the diagram the motor controller chip has two separate power supplies. Firstly it has the same five volts supply as the PIC. This is to power the logic part of the operations. The motors are powered from a separate supply consisting of 16 AAA rechargeable batteries in series giving a total of 20.8V. There are two reasons for this separate supply. 1) The motors will need a higher voltage and current that can be provided from a five volt supply. 2) The motors will generate electrical noise on the power supply lines, This takes the form of voltage spikes (transients) This can

damage the PIC or cause it to execute the code non-sequentially – this less than helpful!

Typical voltage spikes from a DC motor.

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Here I test the accelerometer by measuring the output voltage on a multimeter. The images show the voltages given off on the X,Y and Z axis. This however was not clear enough as the multimeter was not fast enough to respond due to its low polling rate. I then replaced the multimeter with a oscilloscope. This provided a graph where I could easily see the rate of change in the voltage. The voltages vary as the accelerometer moves in that axis so I can use the ADC pins on the PIC chip to interpret the voltage as numbers to decode. An example of this can be seen on the next page.

OSC

+5V

Accelerometer

0V

X-Axis

Y-AxisZ-Axis

V

+5V

Accelerometer

0V

X-Axis

Y-AxisZ-Axis

Practical Investigation 1

I changes the oscilloscope to the other outputs to measure all three axis.

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How an ADC works

SAR – Successive approximation register, a logic unit which can produce binary numbers.

DAC – Digital to Analogue converter, converts the number produced by the SAR back into a analogue voltage.

The comparator compares the DAC voltage to the input voltage (V in) – this input voltage is the one you want to convert into its closest binary number.

If the DAC voltage is greater than the input voltage the output from the comparator is high.

The conversion sequence –

1. The SAR sets the most significant bit (MSB) to 1, in a 4 bit converter the SAR would produce 1000.

2. The DAC converts this into a voltage.

3. The comparator compares this to the input voltage.

4. If it is greater than the input the comparator output is high – the SAR then resets the MSB back to 0 and sets the next MSB to 1 i.e. 0100.

5. The DAC and comparator do their jobs if the output from the comparator stays high this bit is reset and the next MSB is set to 1 i.e. 0010.

6. Eventually the output form the DAC drops below the input voltage- say this happens at 0100, the output from the comparator goes low, the SAR then ‘knows’ this number is less than the input voltage so it sets the next MSB to 1 i.e. 0110.

7. If the output stays low it set the final bit to 1, this then is the closest binary number to the input i.e. 0111

8. If the output goes high then it resets this bit to 0 and tries the next bit i.e. 0101

9. By this cycle the converter eventually produces the output number closest to the input voltage

The PIC can operate both an 8 bit and 10 bit conversion. Hopefully it is clear from the above explanation that the 10 bit would take longer. It would of course offer higher resolution but I don’t think this will be an issue –but it is an option if I need it.

+-

SAR

DAC

Vin

Finished

Start conversion

Read out the finished conversion here

Sample and Hold circuit

There are start and finish signals from the PIC chip which control how long is spent converting each voltage held the sampling circuit. This circuit holds the voltage being converted stopping it from changing mid conversion. Finally after the stop signal is sent each bit of the converted voltage is read off the tracks leading to the DAC.

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Scale on scope is X axis – 10ms/divY axis – 0.1V/div

Change in X-axis – 0.5 divChange in Y-axis – 5 div

Therefore in 5ms the voltage increases by 0.5VTherefore the gradient is

Chan

ge in

Vol

tage

0.

5 Vo

lts

Grad

ient

Lin

e

These results where obtained by moving the sensor very quickly and such would represent a worst case scenario. As you can see it was easily able to respond adequately and was capable of a speed of response of 100VS-1. Also the total response of 0.5 V is more than adequate for the PIC 8 bit ADC. This is because the ADC values range between 0-255 over 0-5V. This means that the response of 5V is change of 26 in the ADC.

8 bit ADC – On-board ADC Sensitivity0-255 – Full range of ADC0V-5V – Range of analogue voltage input0V-0.5V – Change in voltage from sensor0-25 – Change in digital signal


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𝑠=𝑢𝑡+ 12 𝑎𝑡2

𝑠=0.1𝜋𝑢=0𝑎=?1

0.1𝜋=12 𝑎×1

2

0.1𝜋=12 𝑎

0.2 𝜋𝑚𝑠− 2=𝑎0.628𝑚𝑠− 2=𝑎

0.8× 0.6289.81 =51𝑚𝑉𝑔−1

I am using the accelerometer at its 1.5g setting

𝑔=9.81𝑚𝑠− 2

Sensitivity of the accelerometer in V/g

Mathematical analysis of feasibility of using data from the accelerometer

I downloaded the accelerometer specification off the internet and found the typical voltage change per 1g of acceleration.

Here I used calculated the acceleration created when the is moved so when I will not have nasty surprises when I write test code. After calculating the acceleration I related it to the accelerometer by multiplying it by the sensitivity and dividing it by the acceleration due to gravity. This provided me with a final answer of 51mVg -1. This is well with the ability of the ADC to use, as it represents several steps which the ADC can resolve between

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This is the code I used to test the Accelerometerpause 1000serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)serout c.2,n2400,(254,192)serout c.2,n2400,(254,1)serout c.2,n2400,("nothing")pause 1000goto main

main:readadc B.3,b3readadc B.5,b5readadc B.1,b1goto display

display:serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)serout c.2,n2400,("X-")serout c.2,n2400,(#b5)serout c.2,n2400,(" Y-")serout c.2,n2400,(#b1)serout c.2,n2400,(" Z-")serout c.2,n2400,(#b3)goto main

This test bench feeds the accelerometer inputs into the ADC pins on the PIC chip. This cause the PIC to measure the analogue voltages from the three axis of the accelerometer. These are then stored in byte variables before they are outputted onto the OLED screen. By displaying the data I could work out a range of typical values that the accelerometer will send when it is arm mounted so I could write my code appropriately. The range I observed when using it provided me proof that I could control the car using the accelerometer. I as I moved my arm, the range observed was suitable to construct my code around.


This is an circuit diagram for testing circuit. Please note that the voltmeter are not actually there but instead feed into ADC pins on a PIC (not shown).

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Questionnaire1) What would you like the car to be made out of?

1. Metal- 5/102. Wood- 2/103. Plastic 3/10

2)Range of control?4. 1 metres- 1/105. 10 metres- 6/106. 100 metres- 3/10

3) How fast do you want it to go?7. 0.1m/s- 0/108. 0.2m/s- 6/109. 1m/s- 4/10

4) Assuming electrical power, what kind of batteries10. Rechargeable AA - 1/1011. Rechargeable AAA - 2/1012. Sealed rechargeable unit – 7/10

5) What price would you like to pay for it?1. 50-100 – 2/102. 100-250 – 7/103. 250+ - 1/10

6) Would you like waterproofed?4. Yes - 7/105. No - 3/10

7) What length do you want the car to be?6. Under 10 cm - 2/107. Between 10 to 50 cm - 6/108. Above 50 cm - 2/10

8) What kind of motors would you like?9. Petrol powered engine - 4/1010. Brushed electric motors – 2/1011. Brushless electric motor – 4/10

There is a large demand for metal vehicles which have more resistance to damage. However, I cannot prototype a metal design due to lack of time. On the topic of range of control only one person wanted a small range. Far more people wanted a larger range up to a certain point, at which there is fall in numbers because people wanted to be able to see where car was! This is well within the capability of the wireless systems available to me.People generally wanted the car to go fast However, not so fast it was uncontrollable. In terms of power source more people wanted a sealed unit with rechargeable batteries, which interestingly is the same people who later ask for waterproofing. I do not have the time or equipment to develop these features, but I can use rechargeable batteries as a compromise and mount them in position people can easily change/access them.People also generally wanted a low price but were willing to pay for quality. See my costing page for more discussion. There were a lot people who wanted the car to be water-proofed However, it is extremely difficult to do this effectively and given my limited timeframe . Also people want to have a medium sized car, again this is within the envelope my fabrication techniques will allow. People also wanted a petrol motor but it is too expensive and time consuming to add for an initial prototype. I also doubt if people had thought through the difficulties of using such a vehicle indoors!As you can see from my discussion, question 1,4,6 and 8 are unfeasible given my current time frame and tools and as such I have decided on suitable alternative. I will use a plastic case to house the car. I will use rechargeable AAA batteries to power the unit. Also I will use brushed electric motors which will they wear out quickly are a cheap option for a prototype.

I made sure one of the people I asked was the client

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1 Metres10 metres100 metres

0.1m/s0.2m/s1m/s

MetalWoodPlastic

Reachargable AAReachargable AAASealed rechargeable unit

50-100100-250250+

YesNo

<10cm<50cm>50cm

Petrol EngineBrushed electric mo-tors Brushless electric mo-tors

Questionnaire Results

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How to Make a PCBStage 1- Design of PCB

Black FilmPhotosensitive PlasticCopperPlastic

Stage 2- Remove top layer

Photosensitive PlasticCopperPlastic

Protective layer is peeled back at last moment to insure the Room light does not affect the board


Photo mask

UV light

UV light does not get through the ink. The clear area left under UV light is damaged. The equipment used is called a UV light Box

Stage 3- UV light Box

Stage 4- Developer Fluid


UV damaged plastic washed away by Developer Fluid

Turns undamaged plastic black

Stage 5- Etching Tank


N.B Solder through the top layer

Etching fluid removes the copper where it can get to it but not under tracks

UV Light Box Etching Tank

Advantages Disadvantages

Low setup costs Accurate Easy for school

environment Reproducible as I can

reuse the photo-mask.

Toxic chemicals UV Radiation Slow to produce boards

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Step 1This is the basic part of the circuit containing a powered PIC chip.

Step 2This is the next stage in the PIC development with the programing port added.

Controller Circuit board Development Breakdown

Step 3Here I add the switch and the accelerometer inputs.

Step 4Finally I add the LEDs, OLED and XBee output components.

5V

5V5V

5V

Nathan Raj 28

Controller PCB Development Breakdown – I aimed for a compact an economical PCB, with a logical layout and no overlapping components or crossed tracks/jump leads.



Step 3Here I add the switch and the accelerometer inputs.

Step 4Finally I add the LEDs, OLED and XBee output components.

Nathan Raj 29

Controller Breadboard

OLED

XBee

AccelerometerBattery

Programming Ports

PTM Non-latching

On/Off Switch

A breadboard is quick to make and change as you do not have solder components but match to the circuit underlay. This can be complicated with all the jump wires needed to wire it correctly and because of its ease to

remove components it is quite fragile.

Power Indicator

Activity Indicator

20X2 PICAXE Chip

Nathan Raj 30

Car Circuit board Development Breakdown



Step 3Here I add the LEDs and Pads for the ultrasound inputs.

Step 4Finally, I add the motor control and the ultrasound output.

Nathan Raj 31

Car PCB Development Breakdown – I aimed for a compact and economical PCB, with a logical layout and no overlapping components or crossed tracks. I used the minimum of jump leads in order to connect the L293d to the PIC.



Step 3Here I add the LEDs and Pads for the ultrasound inputs.

Step 4Finally I add the motor control and the ultrasound output.

Nathan Raj 32

Car breadboard

A breadboard is quick to make and change as you do not have solder components. However you do have to match the circuit to the pre-existing track arrangement on the breadboard. This can be complicated with all the jump wires needed.

XBee

PCB Batteries

Programming Ports

On/Off Switch

20X2 PICAXE Chip

Motor Batteries

Motor

Ultrasound

L293D

I used a smaller motors for the breadboard prototype as I was only testing the integrity of the circuit. This meant that I only needed 1 battery pack instead of the four I used later on.

Nathan Raj 33

Motor Control Chip- L293D Contains two H-Bridges for both motorsMotor 1

Motor 2

LEDs

Power IndicatorLED Activity Indicator

LEDAccelerometer Input

XBee Output

Current Limiting Resistor



Pull-Down Resistor

PTM Switch

XBee Input20X2 Control ChipContains code

20X2 Control ChipContains code

5V

Separate Power SupplyTo reduce noise and support large current draw of motors

Explanation of Circuits

Comparing it to my specification there is the interconnections for the OLEDs and R/F units. The car circuit can control a H-Bridge so that the range of motion can be fulfilled. The chip clocks at 8 MHz which is fast enough to eliminate noticeable input lag. There are LEDs and an accelerometer and ultrasound as set in the specification. The remaining specification points do not apply to my circuit.

Nathan Raj 34

Comparing Car circuit design to PCB

Power and Switch

20X2 PIC Chip

L293D Motor Control Chip

LEDs This is a good PCB as it has a logical layout and reasonable compact and use minimal jump leads. The coloured rings indicate which part of my circuit matches which part of the PCB layout.

Nathan Raj 35

Comparing Controller circuit design to PCB

Power and Switch

20X2 PIC Chip

PTM Non Latching Switch

LEDs

This is a good PCB as it has a logical layout and reasonable compact and use minimal jump leads. The coloured rings indicate which part of my circuit matches which part of the PCB layout.

Nathan Raj 36

Comparing Controller PCB Design to Auto Router

Auto-routing

My routingFor discussion see next slide

Nathan Raj 37

Comparing Car PCB Design to Auto Router

Auto-routing

My routing

As you can see the auto-routed designs have an illogical layout and a not particularly compact design. Industrially it is the only technique possible for complex circuits. Powerful computers and software can optimally route circuits on multi layer PCB’s.

Nathan Raj 38

Front and Rear View of PCBs

This is was the best view I could obtain given the cramped conditions inside the case

Ribbon cable to reduce clutter inside case

Nathan Raj 39

Circuit I/O Tables

Inputs Pins Outputs Pins

Accelerometer B.5(X), B.3(Z), B.1(Y) OLED C.2

Handshake C.1 XBee C.4

XBee C.6 Power indicator PSU

Activity Indicator B.7

Inputs Pins Outputs Pins

XBee C.6 Leds B.4, B.5

Ultrasound B.3 XBee B.1

Ultrasound C.4

Motors C.0, C.1, B.7, B.6

Controller

Car

Nathan Raj 40

Laser Cutting

Laser cutting works by sending pulses of LASERs which melt the material into a predesigned 2D design. 1. You use a CAD package like 2d design to create a design2. You then import it to the controller of the laser cutter3. The laser melts and engraves using different intensities of LASER4. Remove the cut material and assemble it

Advantages Disadvantages Cuts fast Cuts accurately Needs no moulds Works with a computer Does not go blunt Low cost per unit

Cuts only in 2D Requires expert computer skills High initial setup cost Dangerous Lasers

This technique is highly suitable for my project because• It is extremely quickly , this is important as I have a very limited developmental timeframe• It is accurate, enabling me to quickly and reliable produce matching parts• It uses CAD with all the usual advantages associated with this. e.g. ease of which the design may be

modified or changed, ability to be securely secured won the colleges computer network• It can work on a range of materials although I suspect I will only use only one kind of plastic

For me it is an ideal rapid prototyping system. I can quickly cut precise pieces to form my casings, allowing more time for me to develop the control electronics and coding.

Nathan Raj 41

Potential Controller Designs

This is a simple design which has the user grasp the two sides of box and rotate that in the box in their hands. This However, is not ergonomic to hold so while it would function as a factory prototype it will not a possible realistic design for customers.

This is a more complex design which mounts the accelerometer onto the user’s arm. This allows them to control the car by rotating their arm. This should allow a precise level of control over car. It might take more development time as the shaping is rather complex.

This is a complex design which plays on the theme of a joystick to give a familiarity for the user to control the car. The users needs to hold on the green pole and by twisting their wrist they can control the car. The curved vertical surfaces on the top part are difficult to make on a laser cutter, and probably outside of the available time envelope for this project.

I like the middle one the most. The bottom looks to confusing and the top is a bit boring.

Nathan Raj 42

Prototype development of controller

OLED screen was attached with nuts and bolts

For the top two pictures I created a the design using some spare cardboard to get a rough idea on the overall shape and dimensions as I had no experience of trying to fit something to the human body. With that I could then create a more accurate and rigid prototype on 2D design using laser cut cardboard. The cardboard is cheap and quick to cut and can be recycled.

Switch was attached with nuts and bolts

LEDs was attached with nuts and bolts

Top layer was held up with studding pillars

The shape fits my arm nicely. Can you make the top plate closer to the bottom so my arm isn’t as tired?

Nathan Raj 43

It is simplistic design that uses two pieces of plastic sheet held up by studding pillars. It not an interesting shape so lacks consumer appeal.

Here I have added some shaping to the structure. This add a more interesting shape but will unnecessarily add to the complexity of the design.

This is a simple circular shape which is interesting and unique shape not normally found in children’s toys. As it will collide with people/objects the rounded shape would reduce damage to both parties!

Wheels

LEDs

On/off switch

Potential Vehicle Designs

I like the bottom one the most as look like an alien saucer.

All use 2 rear wheel drive motors for propulsion. Steering is achieved through differential motor drive. For example if one is set forwards and the other backwards the vehicle will turn. The front is a ball caster.

Nathan Raj 44

I created two identical circles with studding holes in the same place. I had two circles on top and bottom to provide extra protection and the better grip the ultrasound wall. On the top circle I added holes for the on/off switch and the programming port. On the bottom I added the holes for the two motors and ball castor and slots for the wheels to sit in. The open frame structure is ideal for prototyping as it allows easy access for trouble shooting and fault rectifying.

Wheel slots

Ultrasound

Ball Bearing Studding Pillars

Wheel slots

On/Off SwitchProgramming Port

Prototype development of car

I used cardboard for the prototypes as it is cheap and easy to cut. As well when I was finished I could recycle all of the cardboard.

The shape is like a UFO!Though that ultrasound looks a lot like a pig’s nose.

Nathan Raj 45

2D Design files sent to Laser Cutter

Holes for studding pillars

Curve of front fits average curvature of my hand

Holes for Velcro straps

OLED

On/Off Switch

LEDs

PTM Non-latching

Ultrasound

10mm LEDs

On/Off Switch

Wheel housing

Interlocking for ultrasound faceplate

360 WheelsMotors

Interlocking allows for secure joins with a high surface area for gluing.

Nathan Raj 46

This is the code I used to test the Accelerometer. It uses an ADC to read the values and then put them on the screen so I can work out what limits I would need for the real codepause 1000serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)serout c.2,n2400,(254,192)serout c.2,n2400,(254,1)serout c.2,n2400,("nothing")pause 1000goto main

main:readadc B.3,b3readadc B.5,b5readadc B.1,b1goto display

display:serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)serout c.2,n2400,("X-")serout c.2,n2400,(#b5)serout c.2,n2400,(" Y-")serout c.2,n2400,(#b1)serout c.2,n2400,(" Z-")serout c.2,n2400,(#b3)goto main

Controller I/O test

This code allows me to test the button by displaying a message on the screen when it is pressedpause 1000serout b.2,n2400,(254,1)serout b.2,n2400,(254,128)

loop1:if pinC.3=0 then loop2goto loop1

loop2:serout b.2,n2400,("Working")pause 100serout b.2,n2400,(254,1)serout b.2,n2400,(254,128)goto loop1

This code allows me to test the receive function on the XBee by receiving numbers and then displaying them on the screenpause 2000low c.2serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)pause 100

serout c.2,n2400,("Receiving")pause 1000serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)goto loop1

loop1:low c.2serin c.6,t2400,($55,$55),b6serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)serout c.2,n2400,(#b6)pause 500goto loop1

Here I display the word nothing on the screenpause 1000serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)serout c.2,n2400,(254,192)serout c.2,n2400,(254,1)serout c.2,n2400,("nothing")

This is the code that I used to the transmit function on the controller XBeepause 2000serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)pause 100serout c.2,n2400,("Transmitting")pause 1000serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)goto loop1

loop1:inc b0serout c.4,t2400,($55,$55,b0)serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)serout c.2,n2400,(#b0)pause 500goto loop1

I tested the outputs before the inputs as I need to activate an output upon the successful activation of the input in order to test them.

Nathan Raj 47

Car I/O Test

This code cause the motors to start turning forwardsPause 500motorcontrol:low c.0high c.1high b.7low b.6

This code tests the Ultrasound by checking the checking the time the signal takes to hit the object in front of it and if is less that 1000 milliseconds away it turns in the LEDspause 1000Ultrasound:pulsout c.4,2pulsin B.3,1,W0pause 20if W0<1000 then gosub ledspause 100goto Ultrasound

leds:high b.4high b.5pause 100low b.4low b.5pause 100return

This code flicks the LEDs on and off againmain:high b.4high b.5pause 100low b.4low b.5pause 100goto main

This code tests the receive function of the XBee by turning the LEDs on if it receives the correct numbers. pause 2000loop1:low c.2serin c.6,t2400,($55,$55),b6if b6> 10 then gosub ledspause 500goto loop1

leds:low c.0high c.1high b.7low b.6pause 5000return

This is the code that I used to the transmit function on the controller XBeepause 2000serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)pause 100serout c.2,n2400,("Transmitting")pause 1000serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)goto loop1

loop1:inc b0serout c.4,t2400,($55,$55,b0)serout c.2,n2400,(254,128)serout c.2,n2400,(254,1)serout c.2,n2400,(#b0)pause 500goto loop1

Again I tested the outputs before the inputs as I need to activate an output upon the successful activation of the input

Nathan Raj 48

YesIs

b5>100?Send Number 81

No

YesIs b5<60? Send Number 82

No

YesIs

b1>100 ?

Send Number 83

No

YesIs b1<65?

Send Number 84

No

YesIs

number 80?

Stops all motors

No

YesIs

number 81?

Forward

No

YesIs

number 82?

Backwards

No

YesIs

number 83?

Left

No

YesIs

number 84?

Right

No

Start

Display ‘All Halt’ on Screen

Send Number 80

Display ‘Hard Right’ on Screen

Display ‘Forward March’ on Screen

Display ‘Fall Back’ on Screen

Display ‘Hard Left’ on Screen

Store number from XBee

Start

The accelerometer produces two analogue outputs into the PIC chip into b1 and b5. Depending on which threshold is triggered in the PIC chip different numbers are sent by the by the XBee.This number is received by the second XBee which interprets it and passes it on to the car’s PIC Chip. This PIC chip controls the LEDs and a L293D chip which as previously discussed can control the DC motors. This allows the user to manipulate the car. The ultrasound scans the area immediately in front of robot and if there is an obstacle it attempts to evade it

Scan Ultrasound Is echo <500

No

Yes

Subroutine evade

Program Algorithm for Car and Controller

Nathan Raj 49

Controller Programming - Problem

• high c.4• low c.2• pause 2000• gosub clearscreen• serout c.2,n2400,("Start-up")• pause 1000• goto main

• main:• readadc B.1,b1• readadc B.5,b5• goto Break

• clearscreen:• low c.2• serout c.2,n2400,(254,1)• serout c.2,n2400,(254,128)• return

• Break:• low b.7• gosub clearscreen• serout c.2,n2400,("Stopped")• let b0=80• goto Break2

• Break2:• readadc B.1,b1• readadc B.5,b5• if b1>100 then Go• if b1<65 then Backwards• if b5<60 then Left• if b5>100 then Right• serout c.4,t2400,($55,$55,b0)• goto Break2

• Go:• gosub clearscreen• serout c.2,n2400,("Forward")• let b0=81• goto Go2

• Backwards:• gosub clearscreen• serout c.2,n2400,("Reverse")• let b0=82• goto Backwards2

• Left:• gosub clearscreen• serout c.2,n2400,("Left")

• let b0=83• goto Left2

• Right:• gosub clearscreen• serout c.2,n2400,("Right")• let b0=84• goto Right2

• Go2:• high b.7• low c.2• serout c.4,t2400,($55,$55,b0)• goto Break• Backwards2:• high b.7• serout c.4,t2400,($55,$55,b0)• goto Break• Left2:• high b.7• serout c.4,t2400,($55,$55,b0)• goto Break• Right2:• high b.7• serout c.4,t2400,($55,$55,b0)• goto Break

This is the initial code that I wrote for the controller. It has an unexpected issue where the XBee units would start to transmit interference to their own signal. I solved the issue by stripping the code to a more basic form and building back to the

functionality seen in V2.

Nathan Raj 50

Controller Programming V2

• high c.4• low c.2• pause 2000• serout c.2,n2400,("Start-

up")• pause 1000• goto Break

• Break:• readadc B.1,b1• readadc B.5,b5• low b.7• let b0=80• serout c.2,n2400,

(254,128)• serout c.2,n2400,(254,1)• serout c.2,n2400,("All

Halt")• if b1>100 then Go• if b1<65 then Backwards• if b5<60 then Left

• if b5>100 then Right• serout c.4,t2400,

($55,$55,b0)• goto Break

• Go:• let b0=81• high b.7• serout c.2,n2400,

(254,128)• serout c.2,n2400,(254,1)• serout c.2,n2400,("Hard

Left")• pause 1000• serout c.4,t2400,


• Backwards:• let b0=82

• high b.7• serout c.2,n2400,

(254,128)• serout c.2,n2400,(254,1)• serout c.2,n2400,("Hard

Right")• pause 1000• serout c.4,t2400,


• Left:• let b0=83• high b.7• serout c.2,n2400,

(254,128)• serout c.2,n2400,(254,1)• serout c.2,n2400,("Fall

Back")• pause 1000• serout c.4,t2400,

($55,$55,b0)

• goto Break

• Right:• let b0=84• high b.7• serout c.2,n2400,

(254,128)• serout c.2,n2400,(254,1)• serout c.2,n2400,

("Forward March")• pause 1000• serout c.4,t2400,


This is the version of code I programmed when I built up from the stripped down code. It use a main loop where it check the accelerometer to work out which variable it needs to transmits and then goes to the relevant loop and sends the number displaying the instruction on the screen before returning the main loop

I am not repeating annotations from previous versions

Nathan Raj 51

Car Programming V2

• pause 500

• Loop1:• high b.4• high b.5• pulsout c.4,2 ;Ultrasound sending wave• pulsin B.3,1,W0 ;Ultrasound storing wave

reflection time• pause 20• if W0<500 then gosub evade ; Analysing

the wave reflection time• serin c.6,t2400,($55,$55),b0; Waits for a

signal on pinc.6 with correct qualifiers• if b0=80 then Break• if b0=81 then SF• if b0=82 then SB• if b0=83 then SL• if b0=84 then SR• goto loop1

• evade: ; If the car is to close to an object it avoids it

• low c.0• high c.1• low b.7• high b.6

• pause 500• low c.0• high c.1• high b.7• low b.6• pause 180• return

• Break:• low c.0• low c.1• low b.7• low b.6• Goto Loop1

• SF:• low b.4• low b.5• high c.0• low c.1• high b.7• low b.6• goto Loop1

• SB:• low b.4

• low b.5• low c.0• high c.1• low b.7• high b.6• goto Loop1

• SL:• low b.4• low b.5• high c.0• low c.1• low b.7• high b.6• goto Loop1

• SR:• low b.4• low b.5• low c.0• high c.1• high b.7• low b.6• goto Loop1

Here I added the code for the ultrasound. This acts as a break where it detects if the user is going to cause the car to collide with a wall and causes it to make a course correction.


This code instructs the car to wait for a signal for the XBee on C.6 before interpreting the variable. The variable cause the PIC to jump a set of instructions for the L293D Motor Control chip to control the motors. There are qualifiers for the XBee to prevent interference altering the normal use of the device

Nathan Raj 52

Photos showing the controller working

This photos show the accelerometer displaying different commands on the OLED indicating that the XBee is transmitting the encoded numbers to the car, as I tilt my arm in different directions.

Nathan Raj 53

Final Design

Studding Pillars

Ultrasound

OLED

Wheels

Motors

On/Off Switch

Virtual Reality - ControllerVirtual Reality - Car

Real Life - ControllerReal Life - Car

The studding pillars are attached using M4 nuts and bolts. The LEDs are friction fit. The on/off switch has its own nuts to attach it through the hole. The OLED and the ultrasound have M2.5 nuts and bolts to attach them to the case.

Client comments

Very impressed in how you were able to model the products before making them.

Nathan Raj 54

Problems and solutions

Issues Solutions Pg.

Differential torque I wrote some code which balanced the motors by switching off the more powerful left motor for short periods of time

62

Broken power switch

All three of these components broken a various points in the prototype construction and testing stage and where replaced which components with full functionality.

#Broken programming cable

Broken ultrasound unit

Car catching on chairs legs because of the wheels I redesigned the casing and housed the wheels inside the body of a car so that the top down profile of the car was a smooth circle which means it can turn without getting caught on any object. This gives it a tighter turning circle as the actuator are closer to the centre of rotation.

44

The processor was struggling to control the wheels, monitor the ultrasound and XBee serial channels simultaneous

I implemented a dual chip systems which uses a dedicated 08M2 chip to monitor the Ultrasound unit which allows it to trigger a hardware interrupt on the main chip when it gets to close to a wall allowing momentum to be reduced from earlier.

58-61

Car travels below speed requested in specification I added two more 6V battery packs to the L293D motor power pin which more than doubled the speed to 0.291 m/s

#

The LEDs were too dim I replaced the LEDs with new brighter units which are rated at 3000mcd #

Nathan Raj 55

Improvements - For Examiner Guidance

On the next few pages I discuss the various improvement I had time to make.

Improvements Page Number

Two way Handshake 55-57

Dual Core system 58-61

Correcting Differential Torque 62

Reprogramming the firmware of the OLED

63

On the next few pages I discuss the various improvement I could make with more time or resources.

Improvements Page Number

Considerations for future improvements 64

Mass Production methods 65-66

Design for Market 67

Future Communications Improvements 68

Nathan Raj 56

No

YesIspinc.1

is pressed?

Display ‘Press button for handshake’

YesIs

number 85?

Transmit 8515 times

No

Start

Display ‘Start Up’ on Screen

Display ‘Connection Successful’ on

Screen


Start

Goto Main Code

Display ‘Connection Pending’

Transmit 8515 times


Is the number

85? Yes

No

Display ‘Connection failed’ on Screen

Display ‘Engine Powering up’ on

Screen

Goto Main Code

The two PIC chips when starting up have a short handshake routine to double check both are functioning properly. When the user presses the button on the controller it display connection pending and transmits the number 85 several times to connect with the car. If the car detect the correct number it sends the number back before entering the main code. The controller then receive the number and if it is 85 it moves into the main code.

Controller

Send 85 x15

Receive 85

Execute control code

Car

Receive 85

Send 85 x15

Execute driving code

Two Way Handshake Routine

I implemented the handshake routine as building’s Wi-Fi utilised the same 2.4GHz Band technology as the XBee RF Chips. I had originally used qualifiers which prevented stray signals from being picked up However, the handshake makes sure the devices are both functioning as intended on start-up. The routine has a number encoded in qualifiers send back and forth between the devices to test their functionality.

Nathan Raj 57

Controller Programming V3

• high c.4• low c.2• pause 2000• serout c.2,n2400,("Start-up")• pause 1000• goto Connection

• Connection:• gosub clearscreen• serout c.2,n2400,("Press button")• serout c.2,n2400,(254,192)• serout c.2,n2400,(" for handshake")• Connection2:• if pinc.1=1 then Ignition• goto Connection2

• Ignition:• gosub clearscreen• serout c.2,n2400,(" Connection ")• serout c.2,n2400,(254,192)• serout c.2,n2400,(" Pending ")• wait 13• let b0=85• Ignition0:• inc b3• serout c.4,t2400,($55,$55,b0)• if b3<15 then Ignition0• serin c.6,t2400,($55,$55),b2

• If b3=85 then Ignition3• gosub clearscreen• serout c.2,n2400,(" Connection ")• serout c.2,n2400,(254,192)• serout c.2,n2400,(" Failed ")• wait 3• Goto Connection

• Ignition3:• gosub clearscreen• serout c.2,n2400,(" Connection ")• serout c.2,n2400,(254,192)• serout c.2,n2400,(" Successful ")• wait 3• gosub clearscreen• serout c.2,n2400,(" Engine ")• serout c.2,n2400,(254,192)• serout c.2,n2400,(" Powering up ")• wait 2• goto Break

• clearscreen:• serout c.2,n2400,(254,128)• serout c.2,n2400,(254,1)• return

• Break:• readadc B.1,b1

• readadc B.5,b5• low b.7• let b0=80• gosub clearscreen• serout c.2,n2400,("All Halt")• if b1>100 then Left• if b1<65 then Right• if b5<60 then Backwards• if b5>100 then Forwards• serout c.4,t2400,($55,$55,b0)• goto Break

• Left:• let b0=81• high b.7• gosub clearscreen• serout c.2,n2400,("Hard Left")• pause 500• serout c.4,t2400,($55,$55,b0)• goto Break

• Right:• let b0=82• high b.7• gosub clearscreen• serout c.2,n2400,("Hard Right")• pause 500

• serout c.4,t2400,($55,$55,b0)• goto Break

• Backwards:• let b0=83• high b.7• gosub clearscreen• serout c.2,n2400,("Fall Back")• pause 500• serout c.4,t2400,($55,$55,b0)• goto Break

• Forwards:• let b0=84• high b.7• gosub clearscreen• serout c.2,n2400,("Forward March")• pause 500• serout c.4,t2400,($55,$55,b0)• goto Break

In this version I added subroutines to clear up some of the most repeated lines of code and introduced a two way handshake. Please see my page on the subject for more information. I also reduce the pause in the loop to 500 so less time is spent in the loop reducing input lag.


Nathan Raj 58

Car Programming V3

pause 500

Ignition:;the handshake waits for the correct numberserin c.6,t2400,($55,$55),b2if b2=85 then Loop0goto IgnitionLoop0:;the handshake now sends the correct number to the controllerinc b3serout b.1,t2400,($55,$55,b2)if b3<15 then Loop0

Loop1:high b.4high b.5pulsout c.4,2pulsin B.3,1,W0 pause 20if W0<500 then gosub evade ; Analysing the wave reflection timeserin c.6,t2400,($55,$55),b0

if b0=80 then Breakif b0=81 then SFif b0=82 then SBif b0=83 then SLif b0=84 then SRgoto loop1

evade:low c.0high c.1low b.7high b.6pause 500low c.0high c.1high b.7low b.6pause 180return

Break:low c.0

low c.1low b.7low b.6Goto Loop1

SF:low b.4low b.5high c.0low c.1high b.7low b.6goto Loop1

SB:low b.4low b.5low c.0high c.1low b.7high b.6goto Loop1

SL:low b.4low b.5high c.0low c.1low b.7high b.6goto Loop1

SR:low b.4low b.5low c.0high c.1high b.7low b.6goto Loop1

This version of code revise the start-up by adding a handshake routine. Please see the page about this topic


Nathan Raj 59

My most significant improvement - Dual Core system

During the testing I found finding the PIC chip was sluggish in responding to ultrasound as it also had to control the motors. The solution was to use a multicore system. Rather than learn how to program a new hardware platform I decided to dedicate a smaller PIC chip to collecting and analysing the data from the ultrasound which then would trigger a interrupt on main PIC chip. Using a software interrupt would slow down the main chip too much as it continues to search for input to go high.

This means I will have to use a hardware interrupt. As I could find no one with any practical experience with this I had to use forums and datasheets to work out how to program this.

To sum up, the larger chip is now simply now simply scanning the XBee input, driving the motors and LEDs. It does not get involved with running the ultrasound system, this has been handed on to the smaller of the chips. The larger chip simply responds to interrupts from the smaller chip. This considerably reduces the processing load on the main processor enabling it to execute its control loops far faster. This reduces input lag from the ultrasound.

Input Process Output

Ultrasound Ultrasound08M2

20X2 MotorsLEDs

Echo Input Trigger Output

Hardware Interrupt

XBeeUser Input

Nathan Raj 60

YesIs

number 80?

Stops all motors

No

YesIs

number 81?

Forward

No

YesIs

number 82?

Backwards

No

YesIs

number 83?

Left

No

YesIs

number 84?

Right

No


From handshake

Scan Ultrasound Is echo <500

No

Yes

Subroutine evade

The circled area indicates the section of the flowchart and algorithm which will be passed over to the 08M2 secondary processor. This will leave the rest of the flowchart in the hands of the main processor (20X2)Communication between the two parts of the system is due to a hardware interrupt. Please see my coding pages for more details.I believe this will be a significant improvement overall and should result in a significant reduction in the lag needed to execute the main control loop. Which handles the inputs from the controller

New program algorithm

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pause 2000b0=%00000010 ;This sets up pinb.1 as hardware interruptgosub interruptenabler ;This line just runs the reset loop quicklymain: ;This is where the normally running code goes;blah;blahgoto main

interrupt: ;This is the code that you want to execute due to the interrupthigh b.5pause 1000low b.5pause 100 b0 = b0 ^ %01000000

interruptenabler:;This is the reset loophInt1Flag = 0;This reset memory location where the flag is storedhintsetup b0 ;This sets up pinb.1 as hardware interruptsetintflags %00000010,%00000010;This sets the PIC chip to monitor the inputreturn; This returns the program to where it was before the interrupt

This is the pin where the interrupt is setup.This is a track from the 08M2 chip

08M2 drives and process ultrasound data

Motor Control Chip- L293D Contains two H-Bridges for both motors

Motor 1Motor 2

LEDsCurrent Limiting Resistor

20X2 Control Chip

Separate Power SupplyTo reduce noise and support large current draw of motors

08M2Ultrasound driver chip

Explaining how improvements works

Nathan Raj 62

No

YesIs

echo<1000

Scan Ultrasound’

Start

Go Forwards

Stop Motors

Single Coremain:high c.0,b.7low c.1,b.6main2:pulsout c.4,2pulsin B.3,1,W0 pause 20if W0<500 then breakgoto main2break:low c.0,b.7goto break

Dual Coremain:pulsout c.2,2pulsin c.1,1,W0pause 20if W0<500 then interruptgoto main

interrupt:high c.4pause 500low c.4pause 300goto main

pause 2000b0=%00000010 gosub interruptenabler main: high c.0,b.7low c.1,b.6goto maininterrupt: low c.0,c.1,b.7,b.6 b0 = b0 ^ %01000000interruptenabler:hInt1Flag = 0hintsetup b0 setintflags %00000010,%00000010return

Single Core vs. Dual Core

In this code “the one and only processor” is responsible for both scanning the ultrasound and driving the motors.

In this code I have split the ultrasound scanning and motor driving between two cores using a hardware interrupt as explained earlier to scan the ultrasound. As you can see from the photographs you can clearly see that there was a significant improvement in response time with the 2 core system stopping significantly quicker (i.e. further away from the wall) than the single core system.

Dual core system

Single core system

This flowchart shows the basic algorithm behind the code running in both systems.I simply tell the robots to move forwards scanning for an object and then stopping.

Nathan Raj 63

Correcting differential torque

Pause 500motorcontrol:low c.0,b.6high c.1,b.7pause 22low c.1pauseus 2goto motorcontrol

Testing Track

Before After

After the beta-testing one complaint was apparent. Due to the various manufacturing tolerances in motors and gearboxes they outputted slightly different torque/power/rpm. This meant that over a meter the car was 16 cm off to the right. I corrected this by turning the left motor off slightly. The exact times are that every 22 milliseconds the left motor is turned off for 2 microseconds. This provide a mark space ratio of 22000:2. The alteration of the ratio is an example of pulse width modulation. I did this by trial and error.

Initial trajectory

Corrected trajectory

16 cm off track 0.8 cm off track

Nathan Raj 64

Reprogramming the OLED

The OLEDs firmware comes with advertising so I enquired after the firmware and got a copy of the full firmware for the OLED driver chip from the manufacturer’s website. I wired a breadboard and reprogrammed the message to my own name. The section of the code which I changed is on the next page. The ability to do this would add to the customer appeal.

18X2 OLED Driver/firmware chip

Power indicator

Testing OLED

Battery Pack On/off switch

#ifdef use_OLED

EEPROM $00, (" Nathan S. Raj ") #elseEEPROM $00, (" Serial LCD ") #endifEEPROM $10, (" 2015 ")

This is the small section of the firmware code which I alter to create my own start-up messae.ge. The rest of the firmware code is concerned with generating the on screen character from the PICAXE serin command. OF course I left alone!

Nathan Raj 65

Other Possible Hardware Improvements

Injection moulding – this gives cases that have thicker plastics which makes cases that are more robust. This also allows for more unique shapes and designs which could make even more visually appealing design which is also ergonomically to hold and the addition of a click-fit battery compartment separate from the rest of the casing (housing motor’s, PCB etc) would be necessary to prevent damage to the circuit boards when changing the batteries. The batteries could even be housed in a sealed section of the casing, and charged through a plug in PSU. Li-Po batteries are typically used with their huge capacity and light weight.

I could use the spare inputs/outputs for new components which can add functionality to the car and controller like a rumble motor in the controller to provide haptic feedback. This could be switched on/off by using a simple transistor interface from the PIC.

Mass produced PCB with surface mounted components so it smaller and cheaper. The PCB’s can be made by pick and place robots at very high component densities. The boards are also highly reliable and resilient. This is because it is a game and will be used in a rough manner and this will reduce the damage. This manufacturing methods will allow for a low per unit cost to increase profit margin.

Injection Moulded Car Bumper which has thick plastic and is typical of the very robust mouldings which can be made using injection moulding.

A ergonomically controller for the palm of the hand An example of a click fit battery

compartment in a remote

A rumble motor for vibrations in the controller

Nathan Raj 66

Injection moulding methodology

Injection moulding is fast, highly accurate and easily reproducible.

1)The screw thread drives plastic pellets along heated barrel.

2) This causes the plastic melts

3) The ram pushes the thread forward in the barrel and injects plastic into the mould

4)Once the plastic cools the mould opens and ejector pins push object out.

Advantages DisadvantagesMultiple injection points – for complex shapes ensures plastic gets into all area’s of the mouldWater cooled moulds – helps set plastic quickly –speeds up production.Lost cost per item allows for large profit margins on products sold.

Short mouldings – If plastic sets too quickly end up with bits missing.Flashing – Plastic seeps out of mould and forms edging around the object.Large Setup costs prohibit use in school environment

Nathan Raj 67

PCB production in Industry - Reflow soldering

While I hand soldered all of my PCBs for the prototypes in a mass production facility wave soldering will be used to swiftly create all the electrical connections with a same high quality joint. Due to how this method works they can only use surface mounted components.

Legs

PCB

Copper track

Solder

Chip

Heat proof wax

PCB moved across top of solder wave

Gaps left where you want a soldered joint

Solder can only form a joint in the gaps in the wax

Wax removed – finished PCB

Wave solder bath – molten solder is pumped up the middle to form a wave of molten solder

Advantages Disadvantages Lost cost per item allows for large

profit margins on products sold. High speed of production allowing

for more product unit to be made.

Large Setup costs prohibit use in school environment.

Requires the use of surface mounted components only.

Not as strong physical connection as through the hole soldering.

Nathan Raj 68

Design for Market

Flush fitting Ultrasound

Latching PTM On/Off Switch shaped like a fuel cap

Translucent windscreen lights up using an LED to signal power status

Wheels enclosed by body of car to prevent damage from crashing

Castor Wheel under to prevent the from of the car from scrapping along the ground

I sketched this design to show what a industrially designed model will look like. Typically it will be made using injection moulding, this is the only technique which can give me the complex shape and level of detail required. It will of course be capable of mass production with this technique, with all the usual economies of scale associated with it. The battery unit will be lithium ion with its very high energy density and low internal resistance enabling it to deliver high performance and high current without overheating. Charging will be the means of an external charging unit and jack plug. This means there will be no user access for the interior. This offers significant advantages from a safety point of view and in terms of reliability as the user cannot “fiddle” with the constituent parts of the vehicle! The PCB will be mass produced using surface mounted technology and reflow soldering. Such boards are highly reliable, easily capable of mass production, and reasonably sturdy to survive collision. PIC would of course be pre-programmed before being placed on the board eliminating the need of programming ports on the system.

Nathan Raj 69

Future Communication Improvements

While testing I initially had problems with getting the car and the controller to talk successfully. When I added the handshake routine this cleared away most of issues allowing for a far faster start up. This however does not prevent a drop off in connection later on in the communication. This means that a future product will need a better way of ensuring communication. After a searching through various forums I was pointed towards a tutorial which should enable me to create a private network group and block any external interference from outside my two RFID chips. This also has an added benefit in that for the final product each XBee pair will only talk with each other so customer can play with friends adding a selling point. This means that the qualifiers in the code will not have to be modified by hand for each car when the code is flashed to them but instead when each XBee initially setup they are instructed to only receive data from a specific MAC address which is it’s partner in crime.

Nathan Raj 70

CostComponents Number Unit Cost Total project Cost (£) V1,V2

PCB 1102 0.0071 0.78

OLED 1 18.00 18

Resistor 14 0.01 0.14

XBee 2 30.19 60.38

20X2 3 3.59 10.77

08M2 1 1.80 1.80

Battery Packs 11 0.98 10.78

Voltage Regulator 3 0.25 0.75

Programming Ports 4 0.40 1.60

5mm LEDs 2 0.08 0.16

10mm LEDs 4 0.26 1.04

Toggle Switches 3 0.59 1.77

Motors 4 10.79 43.16

Wheels 4 25 100

Wheel Hubs 4 4.14 16.56

Caster Wheels 4 2.08 8.32

PTM Non-latching Switch 1 0.28 0.28

Accelerometer 1 9.84 9.84

L293D 2 3.11 6.22

Ultrasound 2 11.99 23.98

SIL 6 0.60 3.60

DIL 6 0.28 1.68

Acrylic 5 6 30

Miscellaneous 8.39

Total 360

These are the prices of the components at the time of purchase. These prices may have changed in the intervening time. The cost for the prototype is greater than the originally planned for £250 as I had to created a second prototype buggy with a multi-core system because ultrasound overhead on the PIC chip was impairing performance. A finished product for market will be cheaper as all the components will be bought in large quantities at trade pricing so due to the economy of scale the cost per unit will be lower allowing for a greater profit margin. Mass production techniques like those I already covered (injection moulding, surface mounted PCB’s) offer low cost per item despite high set up costs, as all costs are spread over many items. My development time/costs would also be spread rather than heaped onto the one product.Outsourcing production to specialist component manufacturers also spreads the equipment set up costs further as these companies would use the equipment for many different clients not just myself.

This is too expensive but my brother explained to me that as a prototype these extra cost were likely to be incurred.

Nathan Raj 71

Accelerometer TestingBreadboard

Designing the circuit boardPCB wizard

Creating the PCB designPCB Wizard

Printing into acetatePhotocopier

Etching the circuit boardEtching tank

Exposing the circuit board to UV lightUV light box

Drilling holes into circuit boardPCB Drill

Soldering in componentsSoldering Iron

Testing components with basic commandsPICaxe Programming Editor

ProgrammingPICaxe Programming Editor

Modifying programPICaxe Programming Editor

Design the case on 2D design2D Design CAD

Create draft of case on laser cutter

Check size measurements of caseVernier Callipers

Print final case into plastic2D Design CAD

Cutting studdingBand Saw

Combining the caseHand Tools

Testing the whole productHand Tools

ImprovementsCombination of above

Total time (47 hours) (Predicted 43 hours)

One square = 1 hourTime Gantt Chart This does not include the time I spent researching or thinking of solutions to problems and improvements.

The discrepancy in time was due to the in when actually manufacturing I had computer trouble which slowed down the workflow or was missing nut and bolts and had to wait for them to be ordered. Also I had not predicted building a second car which would took up some extra time.

Nathan Raj 72

Specification EvaluationUser Requirements: Car should travel at a minimum of 0.1ms-1

Batteries must last one hour Easy to replace batteries The OLED must be visible to read from the

screen at 50cm. The R/F units must be capable of working at

15 meters The car must be able to go forwards,

backwards, and rotating about a point so it turns within its own length

There should be no noticeable input lag from the controller

The vehicle will have streamlined and appealing form

The LEDs must be visible at 2 meters. The accelerometer must intuitively allow

control over the car Ultrasound can reliable detect walls at 10cm Must be able to run over a variety of

domestic materials. The controller must contour to fit the

forearm. Prototype should cost less than £250

Feedback from Users The car is capable of 0.29ms-1. This was measured by timing the car

over 3 metres. This was repeated 3 times and the mean was taken and rounded down to give 0.29ms-1.

The batteries last 2 weeks on a single charge being used intermittently.

The batteries have been replaced by 8 people without instruction. The OLED is visible from 4 metres minimum by the whole group The R/F chips are capable of communicating at 20 metres across

into another room . The car is capable of performing basic movement operations as well

as advanced operations by combining two basic operations. See programming improvement pages

There is a minor input lag due to the car searching for a XBee input. Once it has enters a new loop it stops checking for XBee input and moves the motor control code and cannot check for new inputs.

Users have favourable compared the design to that of UFO The LEDs are visible at 5 metres by the whole group 12 testers used the car without any prior instruction. It is capable of crossing carpet, tarmac, rubber and asphalt. The testers initially complained the screws dug into the arms if they

were not wearing a long sleeved shirt. I can solve the issue by lining the inside with memory foam.

Please see my comments on the costing page

I used standard sockets for the OLED and LED’s. This means that they are very easy to swop for others if needed. For example you could change the colours.

You successfully managed to meet all of the points which is really good.

As the project developed there was a constant flow of development and changes based on testing/practical experience – I have logged this on the previous pages. This table formally evaluates some the other spec points.

Nathan Raj 73

Health and Safety and the Environment

Health and Safety The bare cable has be insulated to prevent short circuits during operation There are no edges on the case sharp enough to cause any harm. The UV light box was sealed, so that no UV light, which can damage people’s eyesight, could escape. Goggles and gloves were used during the use of etching and developing fluid. The developing and etching fluids are toxic and corrosive. If any touched skin they were washed off

with cold water. I also wore goggles when using the soldering iron and the PCB drill to protect my eyes from spitting

solder and breaking drill bits, respectively The soldering iron is hot and all effort must be spent to resist the urge to touch the end. I to 5 minute breaks every 45 minutes to prevent eye strain from programming.

Environmental Issues I used rechargeable batteries so I did not dispose of batteries after their use I used recyclable acrylic for the design so that it can be reused afterwards The programmable PIC chips can be easily reused in a future prototype I used chip sockets so that if the chips got damaged during testing they can be easily replaced without

replacing the board I carefully positioned cuts to minimise wastage of plastic in the laser cutter I created cardboard prototype casing to check the sizing of the case to same plastic wastage on faulty

designs, cardboard is recyclable. I used OLED which provided a better user experience compared to backlit LCD screens which means

that I will need to replace batteries less often as they use little current.

Nathan Raj 74

Strengths Weakness

ThreatsOpportunities• The cost of production per unit is far

higher for me as compered to competitors who can sell a product at profit at half of my production cost.

• Smartphones offer all of the functionality of my product which factors into how my competitors are cheaper.

• The non-traditional design of the controller may put off new customers unused to novel control systems

• Initially I could not verify that communication had been established. See pages 55 & 68.

• The wheels got caught on chair legs. See page 44.

• The cars veered off the right due to differential torque due to manufacturing tolerance in the gearboxes. See page 62

• The processor was struggling to control the wheels, monitor the ultrasound and XBee serial channels simultaneously. See pages 58-61

• I took advantage of handshake to suspend control until it is verified. See page 55.

• I redesigned the car to house the wheel inside the body which increased mobility and improved the aesthetic design. See page 44

• I wrote code which use PWM to correct for the drift from the parallel. See page 62

• I implemented a dual chip systems which uses a dedicated 08M2 chip to monitor the Ultrasound unit which allows it to trigger a hardware interrupt on the main chip when it gets to close to a wall allowing momentum to be reduced from earlier. See pages 58-61

• The market for R/C cars controlled with the body is unsaturated so there is plenty of opportunity

• This novel control mechanism maybe of interest to established toy companies who may want to buy out the company or pair up for a joint venture.

• I can further improve the product by using private network groups on the XBee chips to further improve the experience

Nathan Raj 75

Gallery Page 1

A View of inside of the robot A View of inside of the controller

Wheel slots to prevent the robot getting stuck on chair legs

Velcro strap allow the controller to be individually tightened for each user

Interlocking tabs so I could prototype a 3D object using 2D sheet acrylic

The pillars allow for clearance between circuit board and components on the top shelf.

These steel bolts will be removed from a final product but where left on for the prototype for when I was testing the motors.

Nathan Raj 76

Gallery Page 2 and Final Client Comments

A view of the underside of the controller A view of the underside of the car

Motor nuts are glued in to prevent them rattling loose during operation

Caster Wheels to allow for movement in any direction are attached via nuts and bolts

Battery mounted on the outside for easy changing during the prototype phase

Velcro strap allow the controller to be individually tightened for each user

This is the area that will be lined with memory foam in the next version of the controller design

I love the work that have done for me on this project. I love that you could design a UFO style robot and the QOL things that you have added in the code and hardware like the stopping it colliding with the wall and make it drive straight are nice. I think it is cool the way it fastens on to the arm. It is a very natural way to drive it. The fact it is hard to control makes it fun to use. The open frame design makes it look a bit scary to pick up because I feel like I am going to break it. The market design looks more like a proper design with everything boxed in. I like the way you can spin it on the spot and I like the way it goes reasonable quick

I took on board what my client said and was particularly pleased with what he said about the design of the controller. Again it was good to get positive feedback about the straight driving. I was a bit worried about difficulty of controlling but my client said that it was a fun part of the game. I do agree with his comments about the market design but this is a common problem with prototype.

accelerometer controller robot

Devices & Hardware