EEL 4924 Electrical Engineering Design. (Senior Design) FINAL REPORT. 18 April Project Name: Automatic Camber Adjustment System

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1 EEL 4924 Electrical Engineering Design (Senior Design) FINAL REPORT 18 April 2011 Project Name: Team Members: Name: Nick Tseng Name: Michael Liss Project Abstract: The objective of our project was to develop a system that can automatically adjust the camber of an automobile; the camber was adjusted based on tire temperatures. A thermal sensing module consisting of three infrared non-contact thermometers was constructed to provide the inputs for the system. A PIC microcontroller was used to recognize the difference between the inner and outer tire temperatures and adjust the camber angle. A linear actuator was used to provide the force necessary to achieve this optimal camber.

2 Page 2/29 Table of Contents: Introduction 3 The Problem 4 The Solution 4 System Prototype 5 System Communications 6 Installation 7 Areas Targeted for Improvement 8 Conclusion 9 References 10 Code 11 List of Figures: Figure 1: Example of negative camber... 3 Figure 2: System flow chart... 5 Figure 3: Snapshot of LCD... 6 Figure 4: System Prototype... 6 Figure 5: Conceptualization of system... 7 Figure 6: PCB design of system... 7

3 Page 3/29 Introduction: Wheel alignment plays a critical role in setting the handling and stability characteristics of a vehicle. While most consumers overlook the importance of tuning wheel alignment, racecar teams invest significant time and money to ensure optimal alignment. At high speeds, minor adjustments in alignment can significantly impact the tires ability to grip the road. The major angle being addressed by this project is camber. Camber is the angle made between the vertical axis of the wheel and the axis perpendicular to the ground surface (Figure 1). The camber of a vehicle comes into play during high velocity turns; as the vehicle accelerates through a turn, a horizontal force is exerted onto the wheels.. Figure 1: Example of negative camber

4 Page 4/29 The Problem: Measuring the inside, center, and outside temperature of each tire has become the norm in researching the effects of wheel alignment. The problem lies in capturing the temperature data. The typical process involves running test laps, stopping the vehicle, and measuring the tire temperature with a thermal probe which must make physical contact with the tire surface. This process is inaccurate because during the time required to reach the vehicle and capture data the tire temperature will drop. Furthermore, adjusting the camber of a vehicle is currently a manual process. A mechanic must rotate the camber rod with a tool to manipulate the angle; the current method basically employs a trial and error technique to optimize the alignment. The Solution: The inaccuracies caused by delayed measurement can be reduced by integrating non-contact thermal sensors into the vehicle. Coupling the sensors with Xbees allow racing teams to monitor the tire temperatures without stopping the vehicle. The information captured by the IR sensors will also be used to control a powerful linear actuator mounted on the vehicle. The actuators role is to change the camber of the vehicle by compressing or expanding the camber rod. This addition allows the vehicle wheel alignment to adjust/respond to the driving environment in real time.

5 Page 5/29 System Prototype: The current system is comprised of the following main components: IR sensors, PIC microcontroller, Xbee wireless chips, and a linear actuator (Figure 2). The source code is provided at the end of this report. PIC18 Figure 2: System flow chart

6 Page 6/29 System Communications: I 2 C I 2 C is a two wire interface communication protocol that was used to establish a link between the microcontroller and the IR sensors. I 2 C protocol was selected because of its ability to communicate with multiple slave devices using a single data line. UART The sensors return the temperature data in the form of a 15 bit binary number which the PIC converts into temperature readings by dividing and subtracting from the original value. The three temperature readings are sent to the Xbee using the transmitting line of the PIC s UART. The serial communication runs at 9,600bps to match the default 9,600bps speed of the Xbee modules. PWM The actuator is controlled through pulse width modulation. Altering the percent duty cycle of the PWM square wave changes the percent arm extension accordingly. In manual mode, the duty cycle is controlled by a potentiometer connected to the ADC port on the PIC. In automatic mode, the duty cycle increases by approximately 2% every second until the temperature differential across the tire is nulled. Figure 3: Snapshot of LCD Figure 4: System Prototype

7 Page 7/29 Installation: Mounting the sensors onto the suspension ensures the tire will always stay within the sensors line of sight (Figure 5), at a consistent distance. Insulating the system from the vehicle is crucial to prevent malfunctions due to overheating. Although lightweight packaging is desirable, the system s housing also needs to be robust enough to deflect flying debris kicked up from the tire. Actuator Figure 5: Conceptualization of system Figure 6: PCB design of system

8 Page 8/29 Areas Targeted for Improvement: Throughout the development process, several areas in need of improvement have been revealed: Increased range the 1mW Xbee modules lacks the range to transmit information to nearby engineering teams. A more powerful module is necessary to establish reliable wireless communication. Field of view - the current IR sensors being used have a 90 degree field of view. A sensor with a more focused viewing angle could also be positioned farther away from the tire. Ambient temperature the current sensors cannot produce accurate measurements when exposed to ambient temperatures above 85 degrees Celsius. A similarly priced product was later discovered with a larger operating ambient temperature range, up to 125 degrees Celsius. This upgrade would reduce the sensors sensitivity to the heat generated by the racecar. Real time clock right now the system uses the microprocessor s internal oscillator to count seconds. However, because the PIC is running several different processes simultaneously, the period between clock cycles is inconsistent. Over a long period, the real time clock will fail to accurately reflect elapsed time. External devices with dedicated counters are available to improve time keeping abilities in electronics. Such a device should be adopted in a future design. Thermal insulation the thermal packaging was never created for the current design. The system s housing needs to be developed and tested before the system can be installed onto a vehicle. More powerful actuator Obviously a more powerful actuator will need to be used in real world applications. The actuator used in this project was sufficient only for demonstration purposes.

9 Page 9/29 Conclusion: A new system for tuning vehicle camber is on the verge of revolutionizing the traditional methods. Once a concrete system is introduced into the racing market, the technology will quickly evolve and improve. Implementing the design modifications described will help improve the systems operating accuracy and capability. These improvements will move the prototype one step closer to the consumer market. As with any new technology, additional testing and refining is required before the system can become a viable alternative to the current practices in tuning vehicle camber.

10 Page 10/29 References: 1- "MLX90614ESF Datasheet." Web. Jan < AAA.html>. 2- "PIC18LF46k22 Datasheet." Microchip Technology Inc. Web. Jan < 3- "Wheel and Tire Characteristics." RACELINE CENTRAL. Web. Feb < 4- "L12 Datasheet." Firgelli Technologies. Web. 11 Feb <

11 Page 11/29 Code: #include <p18lf46k22.h> #include <delays.h> #include <pwm.h> #include <i2c.h> #include <usart.h> #include <stdio.h> #include <pconfig.h> #define LINEAR //use linearized readings #pragma config FOSC = INTIO67 #pragma config LVP = OFF #pragma config WDTEN = OFF #define input PORTAbits.RA6 //#define IN1 PORTDbits.RD0 //#define IN2 PORTDbits.RD1 //#define IN3 PORTDbits.RD2 //#define LED PORTDbits.RD3 #define ADDR1 0x20 #define ADDR2 0x22 #define ADDR3 0x24 #define SUCCESS 0 #defineerror 1 char x; unsigned char sensor_addr[3]; float T_ambient[3]; float T_sensor[3]; //general purpose temp int adc_result=102; //used for extracting value from adc int t; //used to display angle int fudge; int time=0; int i; int min=0; int hour=0; int temp0; int temp1; int temp2; int MLX_read(unsigned char,unsigned char); //reads 16 bits from MLX device at addr/register void SetDCPWM1(unsigned int); //sets duty cycle void UpdateTemps(void); //update the 6 temperature readings

12 Page 12/29 void Print(unsigned int); void main() { char temp[7], counter,n; sensor_addr[0] = ADDR1; sensor_addr[1] = ADDR2; sensor_addr[2] = ADDR3; //clear out the temperature array for(n=0; n<3; n++) { T_ambient[n] = 0; T_sensor[n] = 0; //print temperature to LCD ANSELC = 0b ; //Port C is digital IO (not A/D) (I2C will not work if ANSEL bits hi) OSCCONbits.IRCF0 = 1; OSCCONbits.IRCF1 = 1; OSCCONbits.IRCF2 = 1; //16Mhz internal oscillator TRISCbits.TRISC2=0; //set output pin for PWM TRISAbits.TRISA6=1; //set A6 pin to input used to switch between auto and man. ADCON0=0b ; // ADC port channel 3 (AN3), Enable ADC ADCON1=0b ; // Use Internal Voltage Reference (Vdd and Vss) ADCON2=0b ; // used for adc DDRCbits.RC3 = 1; //Configure SCL //as Input DDRCbits.RC4 = 1; //Configure SDA //as Input SSP1STAT = 0xC0; //Enable SMBus & //Disablw Slew Rate Control SSP1CON1 = 0x28; //Enable MSSP Master SSP1ADD = 0xC7; //Should be 0xC7 //for 20kHz w/ 16MHz Fosc // SSP1ADD = 0x27; //Should be 0x27 //for 100kHz w/ 16MHz Fosc SSP1CON2 = 0x00; //Clear MSSP Conrol Bits

13 Page 13/29 BAUDCON1bits.BRG16 = 0; // use 16 bit baud rate Open1USART(USART_EIGHT_BIT & USART_CONT_RX & USART_BRGH_LOW & USART_ASYNCH_MODE & USART_ADDEN_OFF, 25); //open usart port 1 while (!OSCCONbits.HFIOFS); //wait for oscillator stabilization PR2 = 0b ; //don't touch!!! for pwm T2CON = 0b ; //don't touch!!! for pwm CCP1CON = 0b ; //bit 4 and 5 are LS bits keep bits 4 and 5 at 0 and 0 for pwm Delay10KTCYx(0); Delay10KTCYx(130); Delay10KTCYx(0); Delay10KTCYx(130); Delay10KTCYx(0); Delay10KTCYx(130); Delay10KTCYx(0); Delay10KTCYx(130); putc1usart(0x00);// clear LCD putc1usart('i'); putc1usart('n'); putc1usart('s'); putc1usart('i'); putc1usart('d'); putc1usart('e'); putc1usart(0x75); //move to right putc1usart('o');

14 Page 14/29 putc1usart('u'); putc1usart('t'); putc1usart('s'); putc1usart('i'); putc1usart('d'); putc1usart('e'); putc1usart(0x7c); putc1usart(0x0f); putc1usart(55); putc1usart(0x70); putc1usart(0x65); putc1usart(0x05); //draw box while(1){ while(input==1)//main loop { ADCON0bits.GO=1; // for adc while (ADCON0bits.GO); // for adc adc_result=adres; adc_result = adc_result/5; SetDCPWM1(adc_result); t = adc_result/10; t=t-10; UpdateTemps(); //Update the temperature readings putc1usart(140); //move to top

15 Page 15/29 putc1usart(0x43); //move to center sprintf(temp,"%3d'",t); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; //write pwm value to LCD putc1usart(65); //move to middle putc1usart(0x05); //move to left Print(2); putc1usart(65); //move to middle putc1usart(0x43); //move to center Print(0);

16 Page 16/29 putc1usart(65); //move to middle putc1usart(0x80); //move to right Print(1); putc1usart(30); //move to bottom putc1usart(0x23); //move to right sprintf(temp,"%3d ",hour); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; sprintf(temp,":%3d ",min); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; sprintf(temp,":%3d ",time); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]);

17 Page 17/29 counter++; //write outside time value to LCD Delay10KTCYx(0); Delay10KTCYx(120); if(time==59){ time=-1; min++; if(min==59){ min=0; time=-1; hour++; time++; Delay10KTCYx(10); //end main loop while(input==0){ for(i=0; i<1; i++){ UpdateTemps(); putc1usart(140); //move to top putc1usart(0x43); //move to center fudge=adc_result/10; fudge=fudge-10; sprintf(temp,"%3d'",fudge); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; //write pwm value to LCD

18 Page 18/29 putc1usart(65); //move to middle putc1usart(0x05); //move to left Print(2); putc1usart(65); //move to middle putc1usart(0x43); //move to center Print(0); putc1usart(65); //move to middle putc1usart(0x80); //move to right

19 Page 19/29 Print(1); putc1usart(30); //move to bottom putc1usart(0x23); //move to right sprintf(temp,"%3d ",hour); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; sprintf(temp,":%3d ",min); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; sprintf(temp,":%3d ",time); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; //write outside time value to LCD Delay10KTCYx(0); Delay10KTCYx(130); if(time==59){ time=-1; min++; if(min==59){ min=0; time=-1;

20 Page 20/29 hour++; time++; //1secloop UpdateTemps(); temp0=t_sensor[0]; temp1=t_sensor[1]; temp2=t_sensor[2]; if(temp1==temp2){ else if(temp1>(temp2+1)){ if(adc_result>5){ adc_result=adc_result-5; else if(temp2>(temp1+1)){ if(adc_result<199){ adc_result=adc_result+5; SetDCPWM1(adc_result); putc1usart(30); //move to bottom putc1usart(0x23); //move to right sprintf(temp,"%3d ",hour); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; sprintf(temp,":%3d ",min); counter=0;

21 Page 21/29 while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; sprintf(temp,":%3d ",time); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; //write outside time value to LCD putc1usart(140); //move to top putc1usart(0x43); //move to center fudge=adc_result/10; fudge=fudge-10; sprintf(temp,"%3d'",fudge); counter=0; while(temp[counter]!='\0'){ while(busy1usart()); putc1usart(temp[counter]); counter++; //write pwm value to LCD putc1usart(65); //move to middle

22 Page 22/29 putc1usart(0x05); //move to left Print(2); putc1usart(65); //move to middle putc1usart(0x43); //move to center Print(0); putc1usart(65); //move to middle putc1usart(0x80); //move to right Print(1); putc1usart(30); //move to bottom

23 Page 23/29 putc1usart(0x23); //move to right Delay10KTCYx(0); Delay10KTCYx(130); if(time==59){ time=-1; min++; if(min==59){ min=0; time=-1; hour++; time++; void SetDCPWM1(unsigned int dutycycle) { union PWMDC DCycle; DCycle.lpwm = dutycycle << 6; CCPR1L = DCycle.bpwm[1]; CCP1CON = (CCP1CON & 0xCF) ((DCycle.bpwm[0] >> 2) & 0x30); void UpdateTemps(void) { unsigned char n; for(n=0; n<3; n++) { #ifdef RAW T_ambient[n] = MLX_read(sensor_addr[n],0x03); //read ambient from T_sensor[n] = MLX_read(sensor_addr[n],0x04); #endif #ifdef LINEAR T_ambient[n] = MLX_read(sensor_addr[n],0x06); //read ambient from T_sensor[n] = MLX_read(sensor_addr[n],0x07); T_sensor[n]=T_sensor[n]/50.0;

24 Page 24/29 #endif T_sensor[n]=T_sensor[n]-273.0; int MLX_read(unsigned char dev_addr, unsigned char reg_addr) { unsigned char status, data, result_l=0, result_h=0, sign; unsigned int temp; int result; sign = 0; dev_addr = dev_addr<<1; //adjust for RW bit IdleI2C1(); //check for bus idle condition (should always be idle) StartI2C1(); //Send Start bit data = SSP1BUF; //read any previous stored content in buffer to clear buffer full status //****write the address of the device for communication*** do { status = WriteI2C1(dev_addr); //write the address of slave if(status == -1) //check bus { data = SSPBUF; SSP1CON1bits.WCOL=0; while(status!=0); //write until successful communication temp=1; //debug WriteI2C1( reg_addr ); // Write the command (read location) temp=1; //debug IdleI2C1(); // ensure module is idle RestartI2C1(); //repeated start bit // WriteI2C1(dev_addr 0x01); //Send Address with read set WriteI2C1(dev_addr); //Send Address without (Melexis ignores bit anyway) IdleI2C1(); // idle result_l = ReadI2C1(); //read low byte AckI2C1(); //ACK result_h = ReadI2C1(); //read high byte AckI2C1(); //ACK status = ReadI2C1(); //read CRC (but ignore) AckI2C1(); //ACK IdleI2C1(); // ensure module is idle StopI2C1(); // send STOP condition while ( SSP1CON2bits.PEN ); // wait until stop condition is over

25 Page 25/29 #ifdef RAW if(result_h & 0x80) sign = 1; complement) result_h = (result_h & 0x7F); temp = result_h; temp= temp<<8; temp = (temp result_l); result = temp; if(sign) result = 0-result; #endif //get sign bit (device uses sign + magnitude, not 2s //strip sign bit //this is the 16 bit magnitude //change to signed #ifdef LINEAR temp = result_h; temp= temp<<8; temp = (temp result_l); result = temp; #endif //data already in OK format return(result); void Print( unsigned int sensor) { if (T_sensor[sensor] < 100){ TXREG1=(' '); //output 't' to LCD one digit at a time else if (T_sensor[sensor] < 200){ TXREG1=('1'); T_sensor[sensor] = T_sensor[sensor] - 100; if (T_sensor[sensor] < 10){ TXREG1=('0'); else if (T_sensor[sensor] < 20){ TXREG1=('1'); T_sensor[sensor] = T_sensor[sensor] - 10; else if (T_sensor[sensor] < 30){ TXREG1=('2'); T_sensor[sensor] = T_sensor[sensor] - 20; else if (T_sensor[sensor] < 40){ TXREG1=('3');

26 Page 26/29 T_sensor[sensor] = T_sensor[sensor] - 30; else if (T_sensor[sensor] < 50){ TXREG1=('4'); T_sensor[sensor] = T_sensor[sensor] - 40; else if (T_sensor[sensor] < 60){ TXREG1=('5'); T_sensor[sensor] = T_sensor[sensor] - 50; else if (T_sensor[sensor] < 70){ TXREG1=('6'); T_sensor[sensor] = T_sensor[sensor] - 60; else if (T_sensor[sensor] < 80){ TXREG1=('7'); T_sensor[sensor] = T_sensor[sensor] - 70; else if (T_sensor[sensor] < 90){ TXREG1=('8'); T_sensor[sensor] = T_sensor[sensor] - 80; else if (T_sensor[sensor] <100){ TXREG1=('9'); T_sensor[sensor] = T_sensor[sensor] - 90; if (T_sensor[sensor] < 1){ TXREG1=('0'); TXREG1=('.'); else if (T_sensor[sensor] < 2){ TXREG1=('1'); TXREG1=('.'); T_sensor[sensor]=T_sensor[sensor]-1; else if (T_sensor[sensor] < 3){ TXREG1=('2');

27 Page 27/29 TXREG1=('.'); T_sensor[sensor]=T_sensor[sensor]-2; else if (T_sensor[sensor] <4){ TXREG1=('3'); TXREG1=('.'); T_sensor[sensor]=T_sensor[sensor]-3; else if (T_sensor[sensor] <5){ TXREG1=('4'); TXREG1=('.'); T_sensor[sensor]=T_sensor[sensor]-4; else if (T_sensor[sensor] <6){ TXREG1=('5'); TXREG1=('.'); T_sensor[sensor]=T_sensor[sensor]-5; else if (T_sensor[sensor] <7){ TXREG1=('6'); TXREG1=('.'); T_sensor[sensor]=T_sensor[sensor]-6; else if (T_sensor[sensor] <8){ TXREG1=('7'); TXREG1=('.'); T_sensor[sensor]=T_sensor[sensor]-7; else if (T_sensor[sensor] <9){ TXREG1=('8'); TXREG1=('.'); T_sensor[sensor]=T_sensor[sensor]-8; else if (T_sensor[sensor] <10){ TXREG1=('9');

28 Page 28/29 TXREG1=('.'); T_sensor[sensor]=T_sensor[sensor]-9; if (T_sensor[sensor] < 0.1){ TXREG1=('0'); else if (T_sensor[sensor] < 0.2){ TXREG1=('1'); else if (T_sensor[sensor] < 0.3){ TXREG1=('2'); else if (T_sensor[sensor] <0.4){ TXREG1=('3'); else if (T_sensor[sensor] <0.5){ TXREG1=('4'); else if (T_sensor[sensor] <0.6){ TXREG1=('5'); else if (T_sensor[sensor] <0.7){ TXREG1=('6'); else if (T_sensor[sensor] <0.8){ TXREG1=('7'); else if (T_sensor[sensor] <0.9){ TXREG1=('8'); else if (T_sensor[sensor] ==0.9){ TXREG1=('9');

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