group lab report - "racing car"

7/27/2019 Group Lab Report - "Racing Car"

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UNIVERSITY OF EAST LONDON

Group A2Group Design (EE2004)

10th may, 2013

Patrick Vieira

Isabel Coutinho

Samarth Gohil

Course : B.ENG (Hons.) Electricaland Electronics EngineeringYear : TwoSemester : BModule : Group DesignUnit Coordinator : H.hakimazari and K.Yeo


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Table of Contents1 Acknowledgement...............................................................................................3

2 Abstract...............................................................................................................3

3 Introduction.........................................................................................................3

4 Communication and Decisions............................................................................4

4.1 Meetings and Communication.......................................................................4

4.2 Decisions.......................................................................................................4

5 Apparatuses and Components Used................................................................... 6

5.1 The Vehicle:..................................................................................................6

5.2 Basic Specifications & Requirements............................................................7

5.3 Components used......................................................................................... 7

6 Design and Implementation................................................................................8

6.1 The sensors ..................................................................................................8

6.2 Comparator (LM339)..................................................................................15

6.3 Logic Gates................................................................................................. 18

6.4 Driver..........................................................................................................23

6.5 The Gears....................................................................................................24

7 Summary of the Design Evolution ....................................................................25

8 The Race........................................................................................................... 26

9 Conclusion.........................................................................................................28

10 Contribution...................................................................................................28

11 References.....................................................................................................28

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1 Acknowledgement

We would like to show gratitude towards all the group members of A2 to get the

given task done very well before the deadlines. We also would like to thank our

teachers and lab technicians for their support and knowledge they shared with us

during the task and mainly the University of East London for providing us such

environment to work under.

2 Abstract

The aim of this group project is to build a vehicle that meets the agreed

regulations and that is capable to follow the track and ideally complete it without any

physical assistance. The diameter of the vehicle must not excided more than 10

inches and the total cost of the vehicle must not be higher than 55. The track

consists of a line with a contrasting background colour. The track given to us was

black line of 40.5 mm in width in white coloured background board.

3 IntroductionA robot is a machine that can carry out multiple instructions that are provided to it

automatically. The history of robots dates back to 350 B.C., when a Greek

mathematician, Archytas built a mechanical bird known as The Pigeon that was

propelled by steam (NASA). Now with advancement in science and technology

robots are as advanced as Hondas ASIMO (2002), a humanoid robot that was

capable of doing many things humans can do. Robots have been one of mans most

amazing inventions.

The robot (vehicle) developed in this project is a line following robot (vehicle),

which is a mobile machine instructed to follow given path or a line. The final robot

has six sensors installed underneath the back part of the body, and two DC motors

drive wheels. Two comparators and logical gates (one AND gate, one OR gate and

one INVERTER gate) were used to take the signal of the six sensors and control the

wheels. The Infrared Light Sensor used sends infrared light to a surface and the

sensor captures the reflected infrared radiation. The sensor will know if the surface is

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black or white based on the intensity of the light. If it is black surface the output is

logical level 1 and if it is white surface the logical level is 0. The control of the

vehicle is very easy to understand and depends on the position of the six sensors on

the track. A figure representing the track is showed below:

Figure 1: Image of the track

In some cases the vehicle will move forward and other cases one of the wheels

will stop, making the vehicle turn to left or right. Just to illustrate: if the two middle

sensors are senses a black line and all the other four sensors are on white, the

logical circuit will provide an output that tells both motors to go forward. All of the

other cases will be discussed in further sections.

4 Communication and Decisions

4.1 Meetings and Communication

The team decided to communicate via mobile phones mostly and sometimes via

email. To facilitate this, the team members exchanged their details. It was decided

that a weekly meeting was sufficient to successfully complete the project. If anymore

meetings were required, these would be decided by the team as work progresses.Meetings involved practical work and writing the report for the project.

4.2 Decisions

The project was divided into two parts, first was the practical sessions which

consists in twelve weeks of lab group work to produce the vehicle to follow a track.

And the second part was to produce the report which can explain each session and

all the ideas including the ones is not been implemented for various reasons.

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The research for the project was started by just looking into the general areas

provided in the project objectives rather than looking into any specification to

construct a line following vehicle. The result was to use one of the following two

methods: microcontroller or logical gates. Our first option was to build the circuit

using microcontroller and the backup plan was to build the circuit using logic gates.

Microcontrollers are more efficient and it would not be necessary to use so many

components of the laboratory, making the vehicle lightweight. However, after further

researches, it was possible to notice that microcontrollers require a large knowledge

in programming language, and because of the three members of the group do not

have a domain in C and assembly languages, it would be easier to use logic gates.

The final option chosen were completely agreed by all the members of group.

The analysis of the research led to the next step which was to finalise what we

exactly want our vehicle to do by using the chosen methods and what other

supportive components it would be necessary. Thus we came across the designs for

the various circuits we need for each section of the vehicle, such as sensor circuits,

comparator circuit, group of logic gates circuit to get a function to drive the vehicle,

current amplifying circuit and motor driver circuit.

This stage of the project started with building up the circuit on the proto-board

and tested it. Than we moved to the next stage where we build up sensor circuit and

the main circuit on strip board and tested them. We made changes according to the

need and finally made it work perfectly. The main problem was how to arrange the

six sensors on vehicle and that was discovered with try and error basis too. We tried

putting various numbers of the sensors at different distance to get the most possible

accurate response. Same as this we tried to reduce the number of strip boards used

to build the main circuit to keep it compact and less in weight. Another issue foundduring the project was a problem in the gears of one of the motors; the gears were

slipping and the entire buggy was replaced. Finally the vehicle was up to the

requirements of the project and ready to take participate in the race.

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5 Apparatuses and Components Used

5.1 The Vehicle:

Figure 2: Image of the vehicle with the six sensors.

The Image shows the bottom surface of the vehicle. Three ground contact points;

two red wheels and a caster for turning, a fourth point (red arrow) that keeps the

vehicle balanced.

The budget given as mentioned before was 55 which counts the initialcomponents given by the university, the cost of these components make a total of

14.50 which leaves us with a total of 35 to spend in components required to

accomplish the specifications of the project. Unfortunately all the components we

used in our vehicle were available in the university only and them supposed not to

take in account as them will be reused by university. So the list of components and

their prices for our vehicle are given in table 1.

Components Cost Quantity Total

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6V DC motors with

a gear box for each

motor

7.00 2 14.00

A battery

compartment forfour batteries AA

0.50 1 0.50

Total cost 14.50

Table 1: Table showing the cost of the components.

5.2 Basic Specifications & Requirements

Maximum budget: 55

Track: The vehicle can run on

4 AA batteries

Maximum applied voltage: 6V

Strip boards

No excided 10 inches diameter

Proto-boards

Digital Multimeter

Soldering machine

Wires

5.3 Components used

6x Infrared emitter GAAS ( SFH409 RAPID 58-0400)

6x Infrared sensors (SFH309 RAPID 58-0425)

1x Inverter: HEF4049BP

1x AND Gate: HCF4081BE7


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1x OR Gate: HCF4072BE

2x Comparator: LM339N

1x Motor driver: L293D

One variable resistor

Resistor of the following values: 150 , 8.2k, 1k, 15k.

1 Switch on/off

6 Design and Implementation

6.1 The sensors

Infrared sensors (IR) consist of a transmitter and a receiver. They use light to

sense. An LED emits light (transmitter) which is reflected back into a photodiode

(sensor). The amount of reflected light back into the sensors increases as the

distance of the object decreases. IR sensors have disadvantages as most of them

cannot detect objects from far distance such as around 25mm with exceptions to a

few which are very expensive. They can also give error in readings if not kept away

from bright light such as sun light or UV light or interrupted with any other infrared

signals around. Sensors used in our project are Infrared emitter (SFH409 RAPID 58-

0400) and Infrared sensors (SFH309 RAPID 58-0425).

SFH 409 - A light-emitting diode is a semiconductor device that emits visible lightwhen an electric current passes through it.

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Figure 3: Image of the emitting diode.

The specifications of the emitter can be found in Table 2 and Table 3:

Maximum Ratings at 25 C

Description Symbol Value Unit

Operating and storage temperature

range

Tstg 55 ... + 100 C

Junction temperature Tj 100 C

Reverse voltage VR 5 V

Forward current IF 100 mA

Surge current IFSM 3 A

Power dissipation Ptot 165 mW

Thermal resistance RthJA 450 K/W

Table 2: Maximum Ratings at 25 C for the emitter

Characteristics at 25 C


Wavelength at peak emission.

IF = 100 m A,

tp = 20 ms

peak 950 nm

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Spectral bandwidth at 50 % ofImax

IF = 100 m A, tp = 20 ms 55 nm

Half angle 20 Deg

Active chip area A 0.09 mm2

Dimension of the active chip area L x W 0.3 x 0.3 mm

Distance chip surface to lens top H 2.6 mm

Capacitance Co 25 pF

Table 3: Characteristics at 25 C for the emitter

SFH 309 - A phototransistor is a type of photo detector that has the ability of

change light into either current or voltage, depending on the mode of operation.

Figure 4: Image of the phototransistor

Maximum Ratings at 25 C


Operating and storage temperature range Tstg 55 ... + 100 C

Dip soldering temperature 2 mm distance

from case bottom, soldering time t 5 s

Ts 260 C

Iron soldering temperature 2 mm distance

from case bottom, soldering time t 3 s

Ts 300 C

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Collector-emitter voltage VCE 35 V

Collector current IC 15 mA

Collector surge current ICS 75 mA

Power dissipation Ptot 165 mW

Thermal resistance RthJA 450 K/W

Table 4: Maximum Ratings at 25 C for the phototransistor.

Characteristics at 25 C


Wavelength of max. Sensitivity S max 860 nmSpectral range of sensitivity

S = 10 % of Smax 380...1150 nm

Radiant of chip area mm2

Dimension of the active chip area L x W 0.45 x 0.45 mmx mm

Distance chip front to case surface H 2.4 ... 2.8 mm

Half angle 12 deg.

Capacitance CCE 5.0 pF

Dark current VCE = 25 V, E = 0 ICEO 1( 200) nA

Table 5: Characteristics as 25 C for the phototransistor.

The selection of the sensors was a no-brainer, mainly due to the fact there was

no other device provided which could detect the difference between white and black.

It was discussed how they would be placed and tried out different configurations. We

eventually realised that the only way to use them effectively was to have them side

by side, much like an opto-coupler which has been made by hand. As for the number

of sensors, we knew it could be done with three; however we felt that with four, the

buggy would move more accurately along the track (this was also later changedduring the testing stages for six sensors).

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Basically, the four sensors would be in these positions:

Figure 5: Image showing the arrangement of the four sensors.

A picture showing the space of each sensor is showed below:

Figure 6: Image showing the distance from the sensors.

As showed in the picture, the distance between the four sensors that are aligned

is 1in. The two extra sensors were put 1.25 in behind the aligned ones. Another

measurement that is important to consider is the distance of the track to the sensors;

this distance is 0.3 in.

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1 in

1 in

1.25

1.25 in


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After consulting the datasheet, it was calculated the theoretical resistance each

component would have to be placed under in order for their circuitry to melt and

render them useless. Naturally, Ohms Law was a sensible rule to follow and so we

found the lowest possible resistance for each component.

OHMs law:

V = I x R, I is the current and R the resistor

V=6V and IE= 0.1A (from the data sheet for infrared emitter)

So from the OHMs law RE=60

And IS=0.015 (from the data sheet for infrared sensor)

So from the OHMs law RS= 400

The diagram presented below, shows the connections of the sensor and the

emitter:

Figure 7: Emitter and sensor connections, with R1 = RE and R2 = RS, L1 = emitter and

T1 = sensor.

However; as previously mentioned, that was the minimum resistance that each

component could take. Not only that, but after testing the resistors in practice with an

Ohm-meter, they dropped below the theoretical values. This was a problem since we

were risking breaking the components and also using a lot of current which could go

towards running the motor, for example. Some tests helped us deciding which valueswould be better:

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RE () RS () IE (mA)

100 10 47.2

470 470 99.2

150 3.3 k 32.5

270 10 k 18

330 22 k 14.8

560 56 k 8.9

Table 6: Sensors tested to help the decision of which one to use.

In the configuration given below,A white paper at 35mm away from the sensorgives a voltage of 4.1V black gives 4.5V at 35mm. Then 150 was replaced with 330

to test if it is still working. To get the same reading with white paper, it has to be

100mm away and the advantage of that was taking less current thou the

disadvantage was it must be kept close enough to the track. Vehicles platform is

48mm to the lowest part (wheels). Under the same conditions resistors were

changed.

Figure 8: Configuration of the emitter and sensor.

Checking with a different device gave following:

Resistor

values

()

Distance

(mm)

150 30

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330 20

240 21

390 17

463 12

551 10

Table 7: Resistors and the distance of the sensors from the track

The minimum was sound to be 400 but that results in a lot of current being

drown from the battery. After some more tests found that using 1.5 M black

detected 3.6V and white detected 1.5V and below at 10 mm.

After recording many different resistor values for both the sensor and the emitter

as shown before, it was observed that the emitter worked just as well while

experiencing a resistance of 150 and the sensor with a resistance of 8.2k. These

were the values which were implemented into our final circuit and the amount of

current that the six sensors drain was 195mA.

6.2 Comparator (LM339)A comparator is a device that compares two voltages orcurrents and switches its

output to indicate which is larger. In the image beside its the pin diagram is given for

the comparator IC used to make the vehicle. The comparator is essentially an Op

Amp with negative and positive inputs. The voltage at the positive terminal is

compared to the negative one and if the positive terminals voltage was greater than

the one at the other, the Op Amp would adopt the Vccs voltage at its output.

However, if the voltage level at the negative terminal is greater than the positive one,

the Op Amp would adopt the voltage level at ground (zero Volts). An illustration of

the comparator is shown below:

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Figure 9: Operation of the Comparator

The comparator in this case is important to ensure that the input of the logical

circuit will be zero or 6 V, because the output of the sensors is not exactly this

values. A table presenting the values of the outputs of the six sensors are shown

below:

Colour

Logic

1

Logic

0

Pink

(S5) 5.77 1.98Purple

(S1) 5.49 2.02Green

(S2) 5.61 2.47Blue

(S3) 5.53 1.93Yellow

(S4) 5.25 1.49Orange

(S6) 4.9 1.73Table 8: Values of the Sensors

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Our sensor circuit was very well understood. Whenever the pairs heads were

facing a white sheet of paper, the average recorded voltage level amongst all

sensors was [1.936V] and when no infrared light was detected by the sensor, the

average voltage level was [5.425V]. Using this information, a suitable reference

voltage could be decided upon and supplied to the negative terminal of the

comparator. The value decided was 3.68V as it was the average value between the

two values.

The LM339 IC used had four comparators inside it, and each of them worked

comparing its inverting and non-inverting inputs, putting zero or 6 V in the output

depending on which voltage is greater than the other. For the project two

comparators were used, since we used six sensors. The structure and pins of thefirst LM339 are showed below:

Figure 10: Pins of the Comparator

Sensor 1 holds an input by pin 6 and 7, and the output goes to pin 1;




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Sensor 5 holds an input by pin 6 and 7, and the output goes to pin 1 ( this is

in the second comparator)

Sensor 6 holds an input by pin 8 and 9, and the output goes to pin 14

Finally, pin 3 is Vcc and pin 12 is GND. Rest of the pins has no use in thiscase.

With further testing regarding the sensors distance from the track, the voltage

level varied wildly. This would become a problem further down the line when the

decision making process would be implemented. The comparator completely fixes

this problem by adopting one of two ends of the spectrum, maximum voltage and

minimum voltage. One could say that it is demonstrating a logic one and a logic zero.

6.3 Logic Gates

The gates used in the circuit were:

Inverter (HEF4049BP): Inverter is specially used to invert any signal and it

behaves as given in the truth table. In the image at top we can see the symbol of an

inverter, below in the middle we can see the truth table for it and at the bottom its pin

diagram given for the HEF4049BP inverter.

Figure 11: Inverter

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AND Gate (HCF4081BE): The AND gate is a basic digital logic gate that

implements logical conjunction and it behaves according to the truth table given. In

the image beside its symbol of 2 input and gate, in the middle its truth table and at

the bottom its pin diagram for the IC.

Figure 12: AND gate

OR Gate (HCF472BE): The OR gate is a basic digital logic gate that

implements logical conjunction and it behaves according to the truth table given

below. In the image below its symbol of 2 input OR gate at very first, next is the truth

table and at the bottom its pin diagram for the IC. The OR gate used in the project

has four inputs.

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Figure 13: OR Gate

The comparator prepared the buggys design to work in a digital mode. As

previously mentioned, after considering many different aspects of decision making,

logic circuits were decided upon to be implemented.

The first step which had to be carried through was the creating of the truth table

for the four sensors.

Sensor

1

Sensor

2

Sensor

3

Sensor

4 ML MR

0 0 0 0 0 00 0 0 1 1 00 0 1 0 1 00 0 1 1 1 00 1 0 0 0 10 1 0 1 X X0 1 1 0 1 10 1 1 1 1 01 0 0 0 0 11 0 0 1 X X

1 0 1 0 X X1 0 1 1 X X

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1 1 0 0 0 11 1 0 1 X X1 1 1 0 0 11 1 1 1 X X

Table 9: Truth Table of the logic circuit

The group discussed which logics were possibilities that could arise, and then

decided on if they were to arise, what would be sensible for the motor to do. The

logic 1 demonstrates black being detected by the sensor while logic 0 being white.

For the motors ML & MR, logic 1 shows the motor functioning at full capacity while

logic 0 tells it to stop. The X functions were given to logic sequences which could

never happen, as agreed by the group. These functions can therefore be treated as

either logic 1 or 0 since they are essentially dont care functions. An imagepresenting the options is shown below:

Figure 12: Position of the sensors

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The next stage is to produce a Karnaugh Map in order to determine the Boolean

algebra expression for the logic circuit. The groups which are grouped together have

logics in common. Both motors have three loops and so will have three terms in their

expression. The left motor has the expression:

S1S2\S3S4 OO O1 11 1OOO 0 1 1 1O1 0 1 1 111 0 1 1 01O 0 1 1 1

Table 10: Karnaugh Map of Left Motor

Left Motor =

While the right has the expression:

S1S2\S3S4 OO O1 11 1OOO 0 0 0 0O1 1 1 0 111 1 1 1 1

1O 1 1 1 1

Table 11: Karnaugh Map of Right Motor

Right Motor

These two Boolean algebra expressions had to have a schematic made for them,

in how everything would be connected.

This diagram below shows the sensor outputs being fed into the system from the

comparator, not from the sensor itself.

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Figure 13: Diagram Gates

The two sensors entered simply in the OR gates and the left sensor controls the

right motor and the right sensor controls the left motor. Therefore, the final output for

the left motor is:

And the final output for the right motor is:

By the end, the right motor was draining 228mA and the left motor was draining

201 mA.

6.4 Driver

The output signal of the logic circuit does not have the amount current to drive the

motor. So it was needed a current amplifier. To do that, it was used a type of

transistor named TIP 31A. The circuit improved is shown below:

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Figure 14: Amplifier Circuit

After making more researches, it was possible to conclude that if a driver was

used the vehicle could run faster, because it has a faster cut off, therefore, it made

the wheels stop quickly. The IC used was the L293D. The motor driver has the

function of driving two motors simultaneously. This chip enables to take 4 outputs

and turn them into 2 that can be reversed. So two motors can be controlled in both

directions instead of four in only one direction. Disadvantage of this chip is it can be

used to control only small motors, limited to 600mA. There is a 1.5V voltage drop

within the L293D driver chip. The motor driver were used like a common transistors

for the motors

6.5 The Gears

A gear is a rotating machine part having cut teeth which mesh with another

toothed part in order to transmit torque. Two or more gears working in tandem are

called a transmission and can produce a mechanical advantage through a gear ratio.

Such as a small motor spinning very fast can provide enough power for a device but

not enough torque. Geared devices can change the speed, torque, and direction of a

power source. This is how gears are important to look after to maximise the speed of

the vehicle and minimise the power consumption.

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A gear train is formed by mounting gears in a frame so that the eeth of the gears

engage. Gear teeth are designed to ensure the pitch circles od engaging gears roll

on each other without slipping, this provides a smooth transmission of rotation from

one gear to the another.

The gear ratio of a gear train is the ratio of the angular velocity of the input gear

ti the angular velocity of the output gear. The ratio can be directly calculated from the

numbers of teeth on the gears in the gear train and the torque ratio of the gear train

is known as its mechanical advantage.

For the motors & gears used in our vehicle:

No. Of gears Ratio Output shaft (R.P.M)1 9.6 625

2 28.8 208.3

3 86.4 69.4

4 259.2 23.1

5 777.6 7.7

6 2332.8 2.6

7 Summary of the Design Evolution

The original design included four sensors on a small strip board attached to thesupport pillar on the buggy. The group attempted to run the buggy on the test track

using transistors to amplify the current after the logic circuit. The buggy would not

make the turns as the wheels did not come to a stop fast enough.

The conclusion was reached that either we had to find a way to make the wheels

come to a stop faster or build the project with a bit more complexity so that it would

still make those turns regardless of their fault. At that moment in time, each motor

had three gears to drive it and; as it was known that adding in more gears would

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make it slower, that is what the group did to allow the buggy enough time to slow

down, stop and then make the turn. Unfortunately this was unsuccessful as the

wheel still took a long time to come to a halt.

It was noticed that when the wheel finally did come to a stop, part of the buggy

was still hovering above the track. This was consistent with both wheels on both left

and right 90 degree turns. A simple solution then came to light; placing two extra

sensors in the places where the buggy never left the track during the sharp turns

would play nicely into our current design. All that would have to be done is to add the

comparator output for each sensor into the respective OR gate for the correct motor

logic.

This idea played right into the groups hands as they watched their buggy travel

around the track, fault-free. This great success drove the team forward as they

sought ways to make the buggy faster. That was when they came across the motor

driver. This component is just like the transistor, except it looks just like an IC and the

power cut off is much faster. After integrating this into the design instead of the

transistors, the wheels stopped much faster around corners.

Now that the original problem with the buggy was a non-issue, the team took outone gear from each motor to make the total count four in each. This was the final

design which we raced with and came fourth in the competition.

8 The RaceRound 1- Qualifying Stage

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The instructions given to all groups were the same: robots are allowed two turnsin anti-clockwise on the track and the best time will be chosen. It is allowed to touchthe vehicle if needed but 5 seconds will be added to time for each touch as apenalty.

Eight groups emerged winners having time range from 16-50 secs; these groups

are A6,B16, A3, B13, A8, B14, B20, A2.

We had the third best time, 32sec.

Round 2- Quarter Final

Instruction- robots are allowed just one turn in anti clock wise on the track. Withthe same penalty of 5 seconds for each touch in the vehicle.

Now four best timings were chosen for the semi finals. To qualify for the semifinals there was a tie between two cars with 32 sec for the fourth position. One of thecars was ours and the other one was of group B14. So a tie breaker happened.Luckily we won the tie breaker with one second as our vehicle took the 32 secs a ndthe other one took 33secs.

So we were chosen for the semi finals with the other groups as: B16, A3, B13

and A2.

Round 3- Semi Final

Instruction was the same as quarter finals. Now only the best two went for thefinals.

We lost here. We secured fourth place with 32 secs.

Two vehicles selected for the finals were of group B13 and B16 with timings 15

sec and 17 sec in order.

Round 4- Final

Instructions were again same as the semi finals. Now the race was between two

winning cars from semi finals. Final winner won with 15secs best timing. Never theless even runners-up vehicles time was very near too, 16 sec.

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group lab report - "racing car"

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