NATCARAmir SepahmansourMaryam SotoodehMay 16, 2006I. Summary …………………………….…………………………….3Analog DesignPower SupplySensor and Filter NetworkH-Bridge Design OutcomeReferencesNNAATTCCAARR Department of Mechanical and Aerospace Engineering ME106 Fundamentals of Mechatronics Andrew Nguyen Ryan Nunn-Gage Amir Sepahmansour Maryam Sotoodeh May 16, 2006Table of Contents I. Summary …………………………….…………………………….3 II. Introduction ……………………………………………………4 III. Analog Design ………..………………..…………………………5 a. Power Design b. Sensor and Filter Design c. H-Bridge Design IV. Digital Design …………………………………………….…….10 a. ADC Interfacing b. Servo Control c. Motor Control V. Outcome ……………………………………………………….12 VI. References ……………………………………………………….13 VII. Appendix A: Analog Design Layout VIII. Appendix B: Program for Microcontroller IX. Appendix C: ADC SchematicSummary As a group we chose to enter in the NATCAR competition for many reasons. The NATCAR is project, which integrates many different aspects of engineering, such as analog design, digital design, system integration, and mechatronics. In order to have a successful racecar, we needed to design a car that will be able to navigate a preset course as fast as possible. The NATCAR competition required us to build a fully autonomous racecar, which meets the given constraints of the competition. For the analog portion of the car we designed a sensor network, which would inductively pick up the signal from the track. In addition, we needed additional circuitry to regulate the power that would be used for the analog components. In order to autonomously control the car we used a CEREBOT microcontroller to program the steering and speed control. After months of hard work on the project, we successfully built a car that will follow a wire autonomously. We learned a lot about the analog design during testing of the racecar. We learned that the analog design could not handle the amount of current flowing through it and after approximately five minutes of the car running the analog components would get so hot that all the chips would burn out. In addition, we learned a lot about how to program microcontrollers.Introduction The NATCAR competition is an autonomous 1/10th scale car race that is held in the spring every year. The competition is held on the UC Davis campus. The autonomous car must traverse through the track as fast as possible without hitting any border cones. The key to this competition is simplicity. The problem is just trying to get a complicated project such as this to work to its best before adapting fancier solutions to the car. Keep it simple. The closest competition in the past has been UC Berkley and California State University of Sacramento. Competition has been tight sometimes the teams have been within .5 seconds to 122 seconds of each other. The NATCAR project was a comprehensive project that included skills of all the members in the group, which included analog and digital design, system integration, and testing. We had to work together to get all of our components integrated successfully inorder to build a successful car. The car uses inductive sensors to follow a wire with a 100mA and 75 kHz signal. A microcontroller controls the wheel speed and steering angle of the car. We were able to complete the car successfully whit the analog sensing portion of the car on a breadboard. Analog Design Power Supply The NATCAR rules specify that the car must run off of one 7.2V NiCAD battery to supply the power for both the RC car and the digital and analog circuits added. In order to adequately power the analog and digital circuitry a +5V and -5V rail must be established. The positive and negative power supplies were chosen to conserve overall power consumption for the circuits. Since the induced RMS voltage of the signal varies the power consumption of the sensors will end up being equal to, PSENSOR=(VRMS2)/RLOAD Whereas, if we chose a 0 to 10V power supply, the sensor would have to bias the signal with +5V to keep it from being clipped by the power rails. In that scenario the power being consumed will end up being, PSENSOR=(VRMS2)/RLOAD+(52)/RLOAD Since the battery’s voltage will change as it goes from being fully charged to being empty a solution was needed to provide a consistent 5V source to the rest of the circuit. A Low Drop Out regulator or commonly referred to as “LDO” was used as it will step down the battery’s voltage and regulate it to a desired 5V. The LDO will be more than sufficient topower the circuits given that it outputs a maximum 200mA. In the event that circuits require more current 200mA multiple LDOs can be connected to supply the required current. To generate the -5V supply, a charge pump was used to convert the +5V output of the LDO and invert it to a -5V supply. A charge pump works by utilizing strategically placed switches to steer the charging and discharging of a capacitor to obtain the desired output. In order to maintain the charge over the capacitors, the switches must be constantly turned on and off with an internal oscillator. Since the oscillation frequency may introduce noise or EMI to the rest of the circuit, charge pumps are available at different switching frequency. In our application the MAX889T inverting charge pump was chosen since its frequency of oscillation is 2 Megahertz, given that our sensor/filter networks cutoff frequency is at 100kHz, it will reasonably attenuate any noise from the charge pump itself. With the +5V and -5V power supplies established, the NATCAR motor will be driven directly off the battery given that it requires about 10-20A to operate given the load applied to it. The microcontroller will also be driven directly off the battery, because the microcontroller has a built in voltage regulator. The microcontroller will be supplying power to the servo.Sensor and Filter Network The designing of the input sensors is crucial to the success of the NATCAR. The track consists of a wire carrying a sinusoidal 100mARMS signal at 75 kHz, covered in white tape. The designer can choose to sense the track either optically or inductively. Our group chose to sense the track