Project29 Final Paper

7/22/2019 Project29 Final Paper

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UNIVERSITY OF ILLINOIS, URBANA-CHAMPAIGN

Traction Control for the

Formula Hybrid CarECE 445 Senior Design Project

Team # 29

Akshay Ekkundi

Jon Westerhoff

Hyung Seo Park

T.A: Jim Kolodziej

02/24/2011


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Table of contents

1.Objective 31.1 Benefits 3

1.2 Features 42.Design Overview 4

2.1 Block Diagram and Block Descriptions 4

2.1.1 Wheel Sensors 5

2.1.2 Delphi Adaptor 5

2.1.3 NI cRIO 9074 5

2.1.4 NI 9401 5

2.1.5 NI 9205 62.1.6 Celesco CLP-100 potentiometer 6

2.1.7 Controls 6

2.1.8 Motor Torque 6

2.1.9 Regeneration 6

2.1.10 Performance 7

2.1.11 LabVIEW code 7

2.2 Schematics 132.3 Design Alternatives 15

3.Verification 164.Cost analysis and Schedule 19

4.1 Cost Analysis 19

4.1.1 Labor 19

4.1.2 Parts 19

5. Conclusion 21 5.1 Accomplishments 21

5.2 Uncertainties 21

5.3 Future Work 21

5.5 Ethical Considerations 22


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1.Objective:Formula Hybrid is an organization here at the University of Illinois that designs, tests, and races

an open wheeled, formula hybrid racecar. Formula Hybrid brings students from various

disciplines and builds the racecar from scratch. Everything from the chassis to the various

control systems in the car are all built and designed from scratch.

As a part of this project we plan to design and build a traction control system for the racing car.

Traction control is a very important feature in every racing car. It ensures that the car does not

lose traction which leads to losing speed due to loss of traction in the back wheel caused by

excess torque being applied in an effort to go faster. Traction control is an integral part of system

that enables the racing car to be moving as quickly as possible without hindrance.

To implement the traction control we will be using sensors on both the front and the back wheels

to measure the wheel speeds. Base on the measurement, we will determine if each of the back

wheels is spinning either 5% faster or slower than the average speed of the front wheelscombined. In this case our system will calculate the optimum slip and then provide either

positive or negative torque to the back wheels in order to prevent the car from losing traction.

We decided to use the average of the front wheels as we did not want the car to lose speed on

one side because one of the wheels in the front was moving too slow while taking a turn.

Another aspect of our project is to build a system for regenerative breaking in the car so that we

can make the car as efficient as possible but converting its kinetic energy into electric energy and

then storing that energy in a bank of capacitors for later use. This makes the car more efficient

and the car now has power that it can use for various purposes later.

We decided to take on this project as all of us have always been interested in motorsports. We

saw working with Formula Hybrid as a valuable opportunity to gain experience from working

with groups of motivated students whose goal is a title in national competition. We are eager to

apply all the techniques and knowledge we learned here to various aspects of our design such as

on sensors, DSP and control systems.

1.1 Benefits:

Reduces the slippage in the back wheels when excessive positive or negative torqueapplied to it.

Helps the car not lose grip while cornering which will help it obtain optimal speedsand thus aid in getting a faster lap time.

Another important benefit of our system is that it will make the car safer to drive athigher speeds, which is very essential for a race car.

Implementing regeneration will help us recharge the batteries in the car which is agood way of not letting energy go to waste and making the car very efficient.


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In the end our system can be essential in helping the car secure a first place in thecompetition which would be great for us as we will have helped our university win at

a major competition.

1.2 Features:

Automates the traction control. Lab View programming used to implement controls. Potentiometer used at the throttle pedal to implement regenerative breaking.

2. Design overview

2.1 Block Diagram and Block Descriptions

CRIO Controller

Wheel

Sensors

Braking

Motor Regenerati


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2.1.1 Wheel Sensors:

The Sensors that we have decided to use for this project are going to be the Cherry GS101205

Series, Gear tooth speed sensors. These speed sensors are going to be mounted on all the 4

wheels and they will use a gear that will be mounted on the wheel on the wheel that has teeth

with a height of .200 and a width of .100 and a width spacing of about .400. We will use thesesensors to determine the wheel speed of each of the wheels. We shall further use these wheel

speeds to implement the traction control design. The sensor will communicate via a 5V TTL

logic signal.

2.1.2 Delphi adapter

In order to get any information from the Cherry sensors a special adapter is needed. The adapter

is the Delphi 121662280 connector which is specified by the sensor documentation. The adapter

will allow for a water tight connection between the sensor and the wires that run to the cRIO

Module. This is very beneficial as the sensors will be located near the road, and could result inthe assembly getting wet during operation. If the assembly is not waterproof an electrical short

could occur compromising the system as a whole.

2.1.3 NI cRIO 9074

The NI cRIO 9074 is possibly the most important component of our system. All the data

recorded by the sensors is transmitted to the cRIO using the NI 9403 adapter. The cRIO then

uses this information from the Sensors along with the Lab view code written by us, and takes the

appropriate action by increasing or decreasing torque to the back wheels of the car. The cRIO

can do all this processing as there is a FPGA board built into it. The cRIO is also used for other

purposes other than traction control in the system. It has 8 slots and has an input Voltage range

till 30 V which works perfectly for our system.

2.1.4 NI cRIO Module 9401

In order to communicate between LabVIEW code and the instrumentation on the car the hybrid

team is using National Instruments cRIO programmable controller. The controller has 8 bays that

can accept any of a number of input/output modules. These modules can communicate with

digital as well as analog signals depending on specific requirements. The Hall Effect sensors that

were chosen communicate via digital signal which is high when a tooth is in front of the sensor

and goes low when a tooth is not present. The module that was chosen is the NI 9401 which has8 high speed digital I/O channels that are referenced to four COM channels. All the I/O channels

are capable of handling 5 V TTL logic signals. This is a perfect fit for the Cherry Speed sensors

which output a 5V logic signal. The module will be able to accept all four signals from the speed

sensor outputs as well as will be able to output the required control signals to the other devices

on the car.


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2.1.5 NI cRIO Module 9205

The throttle position that is determined based on the output of the potentiometer communicates

via an analog signal. Because of this the module with which communication between the cRIO

and the speed sensors achieved will not be able to communicate with it, because the 9401

module is a digital only module. This means that an analog module will also need to be used.The module chosen for this purpose is the NI 9205 analog input module. This module can

accommodate up to four differential analog signals. This module was chosen because the

differential input will help to suppress any of the noise that might be picked up via transmission

from the throttle to the cRIO. Also because the module has four inputs it will be able to accept

the throttle sensors redundant outputs.

2.1.6 Celesco CLP100 Linear Potentiometer

In order to implement the regenerative breaking we decided to use a linear potentiometer in order

to decide the position of the pedal. The potentiometer has a range of zero to 5Kohms and has alinear output. The potentiometer is rated to be able to handle up to 24V. The input to the

potentiometer was decided to be 12 volts such that when mounted in the car the effective output

range is .67V when the pedal is at zero and 11.5V when the pedal is fully depressed. This was

the best choice as it gave accurate position readings as well as was a standard voltage being used

in the car.

2.1.7 Controls

The controls will assess the situational data from the CRIO and decide the proper course of

action. If the wheels are spinning too fast as indicative of spinning then the controls will decide

whether to apply the brakes or to reduce the motor torque, or both. Depending on which course

of action is taken a signal will be sent to the proper system for action.

2.1.8 Motor Torque

When the controller decides that the motor needs to lessen the amount of torque being put out

this subsystem will reduce the current to the motor such that the torque momentarily drops and

the drive wheels can slow down to regain traction. The controller will also be able to send

negative torque to the drive wheels to assist with the traction control. This will provide the car

with the main form of braking.

2.1.9 Regeneration

The regenerative braking will occur when the driver wants to slow down the car. The amount of

regeneration will depend on the cars speed as well as the position of the throttle pedal. When the

car is at rest and the throttle is at zero percent, no torque will be applied by the motor. As soon as

the pedal is pressed the motor will exert positive torque on the wheels, which will cause the car

to accelerate. This will continue until the car reaches the speed that correlates with the current


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position of the pedal. At this point the torque will drop to a point that cancels out friction and

maintains the current speed. Then when the pedal is released the controller will assess the speed

of the car and compare it to the position of the throttle. If the throttle is at a lower position than

the speed dictates the controller will then decide how much the throttle is below the speed and

apply a proportional negative torque which will slow down the car. This will in turn increase the

EMF in the motor to such a level that it is higher than the battery supply voltage. Thus a current

will be induced to flow into the batteries and recover some of the kinetic energy lost as the car

slows down.

2.1.10 Performance

The systems operation will depend upon several factors: the condition of the track, the condition

of the tires, and the driver. The system should be able to achieve a slip of no more than 5% on all

track conditions. Also the tires should never reach a slip below -5 % when braking. The system

will also need to be able to completely lock the cars tires in the case of emergency.

2.1.11 LabVIEW Code

Figure 2.1 Complete pedal code for throttle and regeneration

The code depicted in figure 2.1 reads the throttle voltage from the potentiometer as well as the RPM

from the motor and uses it to calculate the proper amount of torque to output to the motor. The first

block in the diagram is shown in figure 2.2 and uses the potentiometer voltage as well as user defined

values to calculate the position of the pedal from zero to one. The dead zone is defined by equation 1.

This is the amount of throttle position in which the motor receives no torque command. It is needed so

that if the throttle pedal is accidentally bumped the car does not start running. The pedal position is

then defined by equation 2. After the pedal position is calculated it is sent through a block that limits


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the output to be within the range of zero to one. This is required so if there is a discrepancy with the

minimum or maximum voltage the car does not behave incorrectly.

Vdead= dead*(Vmax-Vmin)+Vmin

Equation 1.

Tpos= (V-Vdead)/(Vmax-Vdead)

Equation 2.

Once the throttle position is calculated it is fed into figure 2.3 to calculate based on the speed of the car

whether to accelerate or decelerate. If the throttle position is less than the current speed from zero to

one then the code assigns equation 3 to be the output, otherwise if the throttle position is greater than

the speed of the car equation 4 is used. The output of this block is then sent to the torque block in

figure 2.4 which turns the amount of acceleration into an acceptable torque amount -.4 to 1. The low

end must be stopped at -.4 such that the motor only regenerates 40% as this is the maximum amount

the batteries in the car can handle.

accel = (RPMmax*Tp - (RPM+1))/(RPM +1)

equation 3.

accel = (RPMmax*Tp-RPM-1)/(RPMmax - RPM -1)

equation 4.

Figure 2.2 Code to calculate pedal position


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Figure 2.3 Code to calculate amount of acceleration

Figure 2.4 Code to assign amount of torque

The code in figure 2.5 is used to read the sensor signal raw and output the speed in both RPM as well as

frequency of teeth passing the gear. The sensor displays a high voltage when there is not a tooth in

front of it and then goes low when there is a tooth. Because of this operation the code generates a spike

whenever the signal returns high after a tooth passes. It then counts the amount of time that passes

until the next pulse is generated. This time is input to a running average that keeps track of the last N

times and outputs the average. This allows for a more accurate reading of the period of the waveform.

Form the period the frequency can then be calculated by taking the inverse of the period. Once thefrequency is known the RPM are easily calculated using equation 5 and the number of teeth on the gear.

RPM = freq*60/teeth

Equation 5.


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Figure 2.5 Code to calculate wheel speed

The code in figure 2.6 implements the traction control system (TCS) using fuzzy logic controller.

Figure 2.6 Traction Control System Algorithm

There are two input variables for the fuzzy logic controller one of which is defined as follow:


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Error=

Equation 6.

where both Front Wheel Speed and Rear Wheel Speed are taken as the average speed of left and

right wheels, i.e.

Front Wheel Speed=

Rear Wheel Speed=

.

The necessity of using average speed of both left and right wheel speed rather than using one of

the two to compute error comes from the observation that the trajectory of each wheel when

vehicle passes corner is different. For instance, when the car turns left at the corner, the path the

left wheel travels is shorter than the path the right wheel travels which implies the speed of the

left wheel is small compared to that of the right wheel.

Another input is change in error and it comes from while loop in bottom left corner. It is defined

as simply the difference between current error and previous error, i.e.

Change in error=Current errorPrevious error

Equation 7.

Those two numerical or crisp inputs for the fuzzy logic controller are fuzzified into membership

functions shown in figure 2.6 and figure 2.7. Note that both inputs have the range of -1 to 1 and

are fuzzified into five membership functions. There is a comprise between the number ofmembership functions and computation speed. A larger number of membership functions will

give more precise results but less computation speed and vice versa.

Figure 2.7 Membership Function for the input Error


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Figure 2.8 Membership Function for the input Change in Error

Figure 2.9 Membership Function for the output Torque

The linguistic output is generated based on the membership function 2.8 and a rule base shown

below.

Conditions Output

Error=Zo Torque=Zo

Error=PmeAND

Change in Error=Not(Big)

Torque=Pme

Error=PmeAND

Change in Error=Big

Torque=Pbig

Error=Pbig Torque=Pbig

Error=NmeAND

Change in Error=Not(Big)

Torque=Nme

Error=NmeAND

Change in Error=Big

Torque=Nbig

Error=Nbig Torque=Nbig

Rule Base for fuzzy logic controller

The output of this fuzzy controller is the amount of torque that needs to be applied to the rear

wheels. It is scaled so that it could be incorporated to the pedal code.


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The processes of fuzzy controller could be summarized into three steps: fuzzification, rule base,

and defuzzification. Fuzzification is a process in which the controller associates crisp or

numerical inputs with the corresponding input linguistic variables using the membership

functions specified for each input. Rule base is used to generate the linguistic outputs.

Defuzzification is the conversion of the output linguistic variable to crisp outputs using

membership functions for the corresponding outputs.

The controller can be optimized by tuning these membership function and it could be done

experimentally.

2.2 Schematics

Sensor Circuit


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Sensor Connection Circuit

Module connections to CRIO

Title

Size Document Number Rev

Date: Sheet of

rev

SENSOR CIRCUIT

A

1 1Wednesday, February 23, 2011

DIO4

DIO3

DIO2

DIO1

DIO12

DIO0

DIO10

DIO9

DIO8

COM

COM

DIO7

DIO6

DIO5

DIO14

DIO13

DIO11

DIO16

RSVD

DIO15

DIO18

DIO17

DIO20

DIO19

DIO23

DIO22

DIO21

COM

COM

DIO26

DIO25

DIO24

DIO29

DIO28

DIO27

DIO31

DIO30

NI 9403

OUTPUT

VCC

GROUND

OUTPUT

VCC

GROUND

OUTPUT

VCC

GROUND

OUTPUT

VCC

GROUND

external power source5Vdc

0

WHEEL

FRONT

LEFT

LEFT RIGHT

RIGHT

GS101205 SENSOR

GS101205 SENSOR

WHEEL

FRONT

WHEEL

REAR

WHEEL

REAR

MODULE

GS101205 SENSOR

GS101205 SENSOR

Title

Size Document Number Rev

Date: Sheet of

red

CRIO - MODULE

A

1 1Thursday, February 24, 2011

NI 9404

9074

NI CRIO

Module

RS-232 4

1A2A3A4A5A6A7A8A9A

RS-2325

1A2A3A4A5A6A7A8A9A

RS-232 6

1A2A3A4A5A6A7A8A9A

RS-232 7

1A2A3A4A5A6A7A8A9A

Module

NI 9215

R S232 0

1A2A3A4A5A6A7A8A9A10A11A12A13A14A15A16A17A18A19A20A21A22A23A24A25A

RS-232

25B24B23B22B21B20B19B18B17B16B15B14B13B12B11B10B

9B8B7B6B5B4B3B2B1B

RS-232 1

1A2A3A4A5A6A7A8A9A10A11A12A13A14A15A16A17A18A19A20A21A22A

23A24A25A

RS-232

25B24B23B

22B21B20B19B18B17B16B15B14B13B12B11B10B

9B8B7B6B5B4B3B2B1B

RS-232 3

1A2A3A4A5A6A

7A8A9A

RS-232 2

1A

2A

3A

4A

5A

6A

7A

8A

9A


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NI 9205 analog input module

2.3 General Design Alternatives

This project has several areas in which it could be improved. The first of these is the regenerative

braking. The current method for regeneration uses a torque limit such that the batteries are not

overloaded when regeneration occurs. This method works just fine for the current hardware in

the car but if the motor are the batteries were to be changed it would no longer suffice. The

remedy to this would be to install instead a current limiter onto the batteries that could be set to

allow only the maximum amount of current for the particular battery pack. This would eliminate

the problem of switching components and not having the correct torque limit such as the

batteries would be overloaded.

The method for enforcing the traction control also has places in which it could be made

more efficient. The method used now is to use the motor to either accelerate or decelerate the

rear wheels based on the average speed of the front two wheels. This only allows for the system

to control the rear tires together. In some situations such as a sharp turn or a slick patch on the

AI2-

AI2+

AI1-

AI1+

AI0-

AI0+

NI 9215

COM

NC

AI3-

AI3+

Ground PP82

Output PP82

Supply +5V 0.2 PP81

Ground PP81

Supply +5V 0.2 PP82

Output PP81

5Vdc

R1

1M

R2

1M


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road one of the tires may slip a lot more than the other and since the average is being used to

detect slip one side may lose traction for a significant amount of time before the system detects

the error. Instead sensors on each side should reference to each other so that if any one tire is

slipping it is easily detected. This would also benefit if the motor is used in tandem with the

mechanical brake system of the car so that all four wheels can be adjusted individually to

maintain optimum traction no matter what the circumstances. However for this to be effective in

tight turns it would be required to calculate the proper amount of excess spin that the outside

tires would encounter. This could be done by using the cars physical dimensions as well as

sensor to detect the radius of the turn.

3.Verification

All four sensors mounted on the vehicles were successfully tested using portable multimeter and

5k pull-up resistor connected in series with the sensors. High voltage ( was detected for

each case when the wheel was spinning and the voltage was low ( ) when the wheel was

stationary. The code for receiving the sensor data and outputting the wheel speed was also tested

using a single gear and was able to accurately display the speed(as shown in figure 3.4). TCS can

be tested using data logging and observing how the car behaves differently based on the speed vs.

time plot. Unfortunately, we were not able to test or demonstrate that traction control system

works fully due to malfunctioning of control box. The outputs generated by LabVIEW, however,

indicate that the code for TCS is fully functional. Shown below are the results in several different

scenarios.


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Figure 3.1 Output for the system when error is within 5%

As designed, output torque when the error stays within 5% as expected.


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Figure 3.2 Output for the system for positive error

Positive output is generated when the error is positive, i.e. the velocity of the front wheels is

larger than that of the rear wheels. In such case, positive torque will be applied to each real wheel.

Figure 3.3 Output for the system for negative error

When the error is negative, i.e. when the rear wheels are spinning faster than the front wheels,

negative torque or brake is applied to each rear wheels.


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Figure 3.4 screen shot of data acquisition code test

4. Cost and Schedule:

4.1 Cost Analysis

4.1.1. Labor

Akshay Ekkundi $ 55/hr x 2.5 x 200 hrs = $ 27,500.00

Jon Westerhoff $ 55/hr x 2.5 x 200 hrs = $ 27,500.00

Hyung Seo Park $ 55/hr x 2.5 x 200 hrs = $ 27,500.00

Total Labor Costs $ 82,500.00

4.1.2. Parts

Cherry GS101205 Gear tooth Speed Sensor

Quantity Needed:6 Retailer:Newark InOne Price/Unit:$ 32.03

Total Price:$ 192.18


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LabVIEW Full

Quantity Needed:1 Retailer:National Instruments Price/Unit:$ 2,599.00

Total Price:$ 2,599.00

Delphi Automotive connectors 3P FM Gray CON ASSY 150.2 SERIES

Quantity Needed: 8 Retailer:Mouser Electronics, Inc. Price/Unit:$ 3.39

Total Price:$ 27.12

NI CRIO Adapter Module 9401

Quantity Needed: 1 Retailer:National Instruments Price/Unit: $ 369.00

Total Price: $ 269.00

NI 9934 25pin D-Sub connector kit

Quantity Needed: 1 Retailer:National Instruments Price/Unit: $ 369.00Total Price: $ 109.00

NI CRIO Adapter Module 9205

Quantity Needed:1 Retailer:National Instruments Price/Unit:$ 499.00

Total Price:$ 799.00

NI cRIO 9074

Quantity Needed:1 Retailer:National Instruments Price/Unit: $ 2,699.00

Total Price: $ 2,699.00

Celesco CLP100 Linear Potentiometer

Quantity Needed:1 Retailer:Celesco Price/Unit:$ 289.00

Total Price: $ 289.00

Pull Up Resistors [2 Watts] Multiple Values:

1000 Ohms

Quantity Needed: 8 Retailer:BC Components Price/Unit: $ 0.68

Total Price: $ 5.44

1800 Ohms

Quantity Needed: 8 Retailer:BC Components Price/Unit:$ 0.68

Total Price: $ 5.44


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2400 Ohms

Quantity Needed: 8 Retailer:BC Components Price/Unit:$ 0.68

Total Price:$ 5.44

3000 Ohms

Quantity Needed:8 Retailer:BC Components Price/Unit:$ 0.68

Total Price:$ 5.44

Total Price of Parts: $ 7,005.06

Total Cost [Labor + Parts]:

$ 82,500.00 + $ 7,005.06 = $ 89,505.06

5. Conclusion:

5.1 Accomplishments:

The LabVIEW algorithms were vital to this project. The algorithms that were created in

LabVIEW were successfully able to recognize when there was a difference in the speeds in the

front and the back wheels and take the appropriate action accordingly. The pedal code also

worked properly however the regeneration had to be limited to 40% so as not to overcook the

batteries. The low voltage control box housing the cRIO was successfully wired and mounted

onto the car. Similarly the sensors were also mounted onto the wheels successfully.

5.2 Uncertainties:

The main aim of the project was to implement traction control on the car and make sure that the

system works at high speeds when the car is moving around a circuit. However due to delays

with the Formula Hybrid team in assembling the car, the whole system could actually be tested

on the car. Although all the modules worked separately in the lab and theoretically, we did not

have the time to test them all together. Thus one uncertainty would be to see how efficiently the

whole system worked and if any tweaks would be required. Another uncertainty was that we

limited the regeneration to 40% by imposing a torque limit, so as to not overcook the batteries.

This method worked for the car however it definitely was not the most efficient method. A

possible correction to this method would be to add a current limiter going into the battery; thiswould make the system more efficient.

5.3 Future Work:

This was the teamsfirst attempt at creating a traction control system for the car and the end

product was a pretty good one. However this product should be used as a stepping stone for more


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efficient and accurate traction control and regenerative breaking systems. The University of

Illinois is going to continue to take part in the completion in the future. For the future cars, our

product should be used however tweaks such as more accurate sensors, reducing the error from 5%

to 3% should be attempted to be done. With enough time and research this is very possible and

this product can be easily transformed into a much more accurate and efficient system. Also for

the regenerative breaking research should be done as to how to increase the regenerative capacity

from 40% to 100% regeneration. Better equipment and more efficient code will definitely aid in

this being able to happen.

5.4 Ethical Consideration

If the traction control does not function properly, for instance, when the system fails to lock up

all wheels when it is supposed to, the driver will loses control of his car and face potentially

serious danger. Therefore, it is essential to make sure that our code is redundant and thoroughly

tested.

References:

[1] "NI CRIO-9074 - Integrated 400 MHz Real-Time Controller and 2M Gate FPGA - National

Instruments."National Instruments: Test, Measurement, and Embedded Systems. Web. 04 May

2011. .

[2] "NI 9205 - 32-Ch 200 MV to 10 V, 16-Bit, 250 KS/s Analog Input Module - National

Instruments."National Instruments: Test, Measurement, and Embedded Systems. Web. 04 May

2011. .

[3] "NI 9401 8 Ch, 5 V/TTL High-Speed Bidirectional Digital I/O Module."National

Instruments: Test, Measurement, and Embedded Systems. Web. 04 May 2011.

.

[4] "Cherry GS101205 Series." Cherry Switches, Sensors, Keyboards and Automotive Modules.

Web. 04 May 2011.

.

[5] "Linear Potentiometer." Celesco. Web. 4 May 2011.

.

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Project29 Final Paper