FINAL PROJECT REPORTMechanical Engineering 224Professor EspinosaJune 9, 2005Kendra ArmstrongNick EcclesCary MaguireAlex TaamPaul Williams2Table of ContentsI. IntroductionII. Boe-Bot AssemblyIII. Servo CalibrationIV. Gyroscope CalibrationV. Analog-to-Digital ConverterVI. Programming and DebuggingVII. Results and ConclusionsVIII. Improvements and Future ConsiderationsIX. Appendix A: Servo Calibration ProgramX. Appendix B: LabView Program for Gyroscope CalibrationXI. Appendix C: Turn Test ProgramXII. Appendix D: Final Path Program3I. IntroductionThe objective of this project is to use our knowledge acquired in Mechanical Engineering224 to control a Boe-Bot along a specified path,Figure 1 – Robot Pathusing gyroscope sensing in a closed-loop feedback system (see figure 1). The Boe-Bot robot ismainly composed of two servo motors to operate the wheels and a Board of Education carrierboard, which is controlled by a program called BASIC Stamp. Specifically, we will create aBASIC Stamp program that will use a specified voltage, which corresponds to a certain angularvelocity, to control the direction of travel of the Boe-Bot. Then, using closed-loop feedback froma gyroscope and ADC (Analog-to-Digital Converter), the Boe-Bot will correct itself to travel in acompletely straight line.4II. Boe-Bot AssemblyFigure 2—Boe BotOur Boe-Bot was brand new, therefore unassembled. First, we attached the fourstandoffs to the four corners of the chassis. The standoffs support the Board of Education fromwhich the Boe-Bot runs. After centering the Parallax Continuous Rotation servos, we attachedthe servos to the chassis using Philips screws and nuts. We then attached our power source, thebattery pack, to the underside of the chassis. After that, we attached the tail wheel ball and highquality rubber band tires. Lastly, we connected the Board of Education onto the four standoffs,with the breadboard closest to the drive wheels. And the Boe-Bot was born! (See figure 2 for aphoto of an assembled Boe-Bot).5III. Servo CalibrationFigure 3 – Boe Bot ServoBefore assembling the Boe-Bot, we had to calibrate the servo motors (see figure 3). Weused a program (see Appendix A) that sends the servos a signal, telling them to stay still.Because the servos are not pre-adjusted at the manufacturing facility from which they came, theywill actually start spinning. We then had to use a screwdriver and adjust the servos until theywere still. This calibration is called centering the servos. When the program input is PULSOUT12, 750, it is centering the right (designated by 12) servo to stay still (750 designates nomovement in either direction). When the program input is PULSOUT 13, 750, it is centering theleft (designated by 13) servo to stay still. When the input 750 is increased, the servo will travel inone direction, and when it is decreased, the servo will travel in the opposite direction.6IV. Gyroscope CalibrationThe main programming softwares we used in this project were LabView and BASICStamp. While we were capable of programming the Boe-Bot to travel in straight lines and makevarious turns with BASIC Stamp, we did not know the actual angles the Boe-Bot turned duringits test trials. In order to be more accurate with our Boe-Bot following its respective path, weintegrated the response of a gyroscope in a closed feedback loop, which will allow us to programthe robot to make turns at specified angles and will adjust the Boe-Bot so it does not deviate fromits straight path.In this project, we used an ADXRSS150EB gyroscope from Analog Devices. It operateson a 5 Volt power supply and is capable of sensing up to 150 degrees in angular motion. Thisgyroscope contains two polysilicon sensing structures which have capacitive pickoff structuresthat are capable of detecting motion caused by a Coriolis force. This Coriolis force is producedwhen the Boe-Bot rotates. After the Boe-Bot rotates, the Coriolis force causes the twopolysilicon sensing structures to be displaced orthogonal to the vibrating motion of the Boe-Bot.The capacitive pickoff structures on the polysilicon sensors then pick up the Coriolis motion anda rate signal output is produced. This rate signal is the feedback we need in order to ensure thatour Boe-Bot turns at specified angles and follows a straight path.Before we wrote our final program, we needed to calibrate the gyroscope and determinethe relationship between its angular velocities and their respective output signals. We firstcreated a LabView program (see Appendix B) that plotted our gyroscope output signals versustime:7Figure 4 – Gyroscope ResponseThis allowed us to see how the gyroscope output signals varied as the Boe-Bot spun in aclockwise (from t = 5 s to t = 17 s) and then counterclockwise (t = 17 s to t = 26 s) motion (seefigure 4).The next step was to determine the relationship between the gyroscope’s angularvelocities and their respective output signals. In order to find this relationship we created aBASIC Stamp program (see Appendix C) that spun the Boe-Bot at various angular velocities.After each run, we recorded the number of rotations, and the respective times for each run, theBoe-Bot completed. This enabled find a relationship between the gyroscopes output signals andtheir respective angular velocities. (See figure 5).Voltage vs Time00.511.522.533.544.550 5 10 15 20 25 30Time (s)Voltage (V)8Figure 5 --Gyroscope Calibration CurveAngular Velocity vs Voltagey = 1.3361x - 3.0312R2 = 0.9999-4-3-2-1012340 1 2 3 4 5Voltage (V)Angular Velocity (rad/s)Test DataLinear (Test Data)9V. Analog-to-Digital ConverterAfter mounting and calibrating the gyroscope, we encountered a major problem. Thegyroscope was outputting a voltage in the range of about 0.2V to 4.6V. We needed to incorporatethe full scope of these values in our control of the Boe-Bot. However, the pins on the Board ofEducation of the Boe-Bot can only read high or low. To rectify this problem, we decided to lookinto ADC’s, which could then provide us with a range of values instead of just 1 or 0. Afterresearching various options online, we decided to use the TLC0820AIN, produced by TexasInstruments. (Specification sheet can be found at