Robotic Control with Gyroscopic Sensing Final Project- ME 224 Professor Espinosa 6/10/04 Alex Ahmadi John Hoffman Andres Huertas Azeem Meruani Simcha SingerTable of Contents I. Abstract II. Introduction III. Technology Background IV. Activity 1: Gyroscope Familiarity a. Self-Test b. Calibration V. Activity 2: Robotic Control c. Assembly & Centering Servos d. LabView Control e. BasicStamp Control VI. Activity 3: Robotic Navigation f. BasicStamp & LabView Interaction g. Gyroscope Use VII. Results VIII. Future Work IX. Conclusion X. Appenix A: LabView Programs XI. Appendix B: BasicStampAbstract As a final project for Mechanical Engineering 224: Experimental Engineering, a group of students used LabView and BasicStamp programming, along with gyroscope sensing, to control the motion of a commercially-available robot. The finished product was a LabView user-interface where a user could input distances to travel, angles to turn and directions, and the 2-wheel cart navigates with gyroscope displays of the angle. Unfortunately, LabView cannot generate pulse-trains for servos in real-time, which is why BasicStamp was included in the project. Overall, the project provided a way to apply our class knowledge through programming and experimental setups. Introduction Throughout the quarter, the class has focused on using LabView for data acquisition and control. In the final project, the objective is to apply class knowledge to control robotic motion with both user input and sensor feedback. Ultimately, the finished product should take inputs from a user through LabView, send signals to a robotic cart, acquire gyroscopic sensing data, and provide angular readouts. The coordinates should be reached within reasonable error (<10%). This project requires much hardware and programming. In the first activity, LabView will be used to calibrate gyroscope readings. LabView programming will acquire voltages proportional to the angular rate of change, which will be integrated to provide angular displacement. Then, in the second activity, robotic control via user input will be explored. User inputs will control the servo rotation. In the final activity, gyroscopic sensing will allow evaluation of the movement of the robot. Technology Background Gyroscopes A gyroscope is a type of sensor that is used to measure an object’s angular velocity. MEMS technology has been able produce low-cost, resonating gyroscopes that have proven useful for a wide variety of applications. The classical gyroscope uses a spinning mass that is allowed to spin in any angular direction but not to translate. Applying any angular motion will then induce “precession” perpendicular to the applied angular motion and also perpendicular to the spin axis.For fabricating MEMS devices, it is more practical to employ a vibrating gyroscope, which operates on the principle of the Coriolis effect. The Coriolis force is given by the following vector equation, Fc = -2m(ωωωω x vr), where m is the objects mass, ωωωω is the angular velocity of the object, and vr is the object’s linear velocity. It can be seen from the presence of the cross-product operator that the Coriolis force is orthogonal both to the velocity and the spin axis. A vibrating gyroscope electrostatically vibrates a proof mass mounted on springs to resonance in one direction (say, along the x-axis), is subjected to a rotation about another (the z-axis), and this causes a secondary vibration (through the Coriolis effect) of the proof mass along the y-axis. Sensing this motion in the y-direction by using capacitive pickoff structures can tell us the angular rate of rotation about the z-axis. The gyroscope used in this project is the ADXRS150ABG, which is able to sense angular motion up to 150 degrees per second. It operates on a 5 Volt power supply, has the ability to perform a self-test (see next section) and is able to reject outside vibrations over a large range of frequencies. All of the required electronic signal-conditioning and amplification elements are on the same chip as the sensor. This enables it to output a voltage from the capacitive pickoff structures that is measurable and meaningful (after calibration) to the user. Integration of the angular velocity with respect to time can provide the angular position of the object upon which the sensor is mounted. This will be utilized in the experiment. Servo Control Servo motors are light weight, powerful motors with built in electronic circuitry. There are three connections to a servo motor: the control wire (or signal line), the power supply and the ground. To control a servo motor, one must control the duration of the pulses sent along the signal line to the motor, which are typically between 1 and 2 milliseconds, and can move the servo between 0 and 180 degrees, or up to 360 degrees for continuous rotation servos. (The continuous rotation servos are used in this project.) This type of control is referred to as Pulse Coded Modulation. A servo motor is given a pulse every 20 milliseconds. For the Parallax Servo used in this experiment, applying a pulse of 1.8 milliseconds makes the shaft turn the maximum amount, thus producing the maximum angular velocity in one direction. For pulses of 1.2 milliseconds, the shaft turns the maximum amount in the opposite direction, and for pulses of 1.5 milliseconds, the motor’s shaft does not rotate. Activity 1: Gyroscope Familiarity In this activity, the gyroscope’s capabilities will be explored in full. One quick way to verify that the gyroscope works is through a self-test. The gyroscope output can be calibrated through integrations using LabView to give an angular displacement reading. Self-TestThe gyroscope evaluation board used is ADXRS150EB, which has the ADXRS150ABG gyro mounted on top. To evaluate that it actually works, a self-test can be run. The gyro board has 20 pins; the pin with a square solder panel (looking from above) is pin 1. The pins are numbered counter-clockwise. Make the following connections: 1 Pin 1 (AVCC): +5 V 2 Pin 2 (RATEOUT): Connect to multimeter or measuring device 3 Pin 8 (AGND): Ground 4 Pin 12 (PGND): Ground 5 Pin 13 (PDD): +15 V 6 Pin 10/11 (ST1/ST2): Apply varying voltage For a self-test, the RATEOUT voltage should be at ~2.5 V. The gyro board has a logic gate within it; for voltages <1.7 V, the gate is a 0. For voltages >3.3 V, the gate is a 1. 7