Robotic Control with Gyroscopic SensingTeam #1Jason LintkerFabian WittmerTable of ContentsTAbstractA/D ConverterBasicStampFeedback ControlTestingAppendix B – Basic StampIntroductionBoe-bot AssemblyA/D ConverterBasicStamp ProgrammingTestingAppendix B – Basic StampDept. of Mechanical Engineering Robotic Control with Gyroscopic Sensing ME 224 – Final Project Prof. Espinosa Team #1 Stefan Bracher Jason Lintker Fabian WittmerTable of Contents T Abstract Introduction Boe-bot Assembly Basic Components BasicStamp Servos Gyroscope Overview Implementation A/D Converter Overview Implementation Computer Programming Labview – A/D Conversion BasicStamp Data Flow Feedback Control Testing Challenges Conclusions Appendix A – Labview Appendix B – Basic StampIntroduction Each week during this quarter we have conducted labs individually to enhance our skills with LabVIEW and electronic systems. During the final project, we have used the combined knowledge of three team members to create a robot with controlled motion. Our goal was to program a desired route for the robot to follow and use gyroscopic sensing to enable the robot to correct any deviation from that route. Boe-bot Assembly Basic Components The original Boe-bot kit consists of two servo motors and a printed circuit board attached to an aluminum chassis. A breadboard provides a convenient interface for additional electronic devices. This very simple structure allows users to customize the robot design with a variety of features and components. BASIC Stamp The BASIC Stamp 2 module contains its own processor, memory, clock, and an interface with 16 I/O pins. The BASIC Stamp program we created (see A.2) and wrote onto the module allowed us to define a specific route for the robot to follow. Additional features of the program enable the robot to sense any deviation from the desired direction. The robot then responds with a small rotation to correct the error. Servos Two small servo motors are attached to the wheels to drive the robot with a high degree of accuracy. Servos use built in circuitry to monitor the signal from a potentiometer which is connected to the output shaft. In this way, the servo can control the angle of the output shaft at all times. This angle is controlled with coded signals sent from the circuitry of the robot. Changes in the signal cause changes in the angular position of the shaft, creating motion of the robot. This type of servo control is referred to as Pulse Coded Modulation. In basic terms, the length of the pulse determines the direction and speed of rotation. Gyroscope Overview A classical gyroscope is a device consisting of a spinning mass, typically a disk or wheel, mounted on a base so that its axis can turn freely in one or more directions and thereby maintain its orientation regardless of any movement of thebase. When spinning, the gyroscope has special properties. Many spinning objects exhibit some of these properties; the rotation of the earth about its axis gives it the properties of a huge gyroscope. Once a gyroscope starts to spin, it will resist changes in the orientation of its spin axis. For example, a spinning top resists toppling over, thus keeping its spin axis vertical. If a torque, or twisting force, is applied to the spin axis, the axis will not turn in the direction of the torque, but will instead move in a direction perpendicular to it. This motion is called precession. ZYX Ω Rate of Rotation Moving Object Vacor = 2V x ΩINVENSENSThe upcoming technology, however, is part of the Micro-Electro-Mechanical Systems family (MEMS). This implementation does consist of a vibrating mass rather than a spinning one. The principle used to measure the angular acceleration is the Coriolis effect. Whenever a mass is moved in a rotating system a force act on the mass. This force is called Coriolis force and is proportional to the angular velocity of the system and the velocity of the mass. Fig. 1 Coriolis accelerometer concept (INVENSENS) MEMS gyroscopes are already used in the car industry for navigation systems. Implementation The gyroscope used in this project is the ADXRS150ABG, built by Analog Devices. It induces a voltage signal proportional to the angular rate of change. Up to 150 degrees per second are detectable. The power supply is a 5 Volt DC signal. The output ranges from 0.25V to 4.75V. No motion equals 2.5V In order to check the gyroscope is working, we hooked it up to an oscilloscope. In the resting state we got a signal of 2.48V. When turning the gyroscope, the signal in- or decreased depending on the direction. Usually, a calibration is needed for further operations. This means the gyroscope is spun at a different velocities, simultaneously the voltage output is acquired. With a curve fitting tool one gets the voltage in dependency of the angular rate of change. Fig. 2 Gyroscope However, for several reasons we decided on not to do a classical calibration. First of all, neither the absolute voltage value nor the angular rate of change is of interest inthis project. We are only interested in the angle. So, the angular rate of change needs to be integrated once. By calibrating before the integration errors would be summed up and propagate. Therefore a calibration with respect to the angle is reasonable. In the numerical integration approach we use, a constant time increment of one unit is assumed. Therefore, the integrated value depends on the frequency of data acquisition. The frequency in turn depends on the amount of code in between each cycle. This means that a calibration of the gyroscope is not reasonable until the final version is ready. Only at this point the parameters can be adjusted. A/D Converter Overview An A/D Converter converts a voltage in a digital number. We used an ADC0804LCN, as our basic stamp had no A/D converter included (just digital inputs). Specifications of the ADC0803LCN: Fig.4 Pins of the ADC0804LCN – 8bit converter – Can be used with internal or external clock – Analog input range 0 V to VCC – Single 5 V supply " – Guaranteed specification with 1 MHz clock Fig. 3 A/D converterFunction The conversion is started with a pulse at the WR pin, and the CS pin on low. As it is an 8bit converter, VCC will be represented by the number 256 and 0V with 0. When the conversion is complete, the INTR pin will make a high-low conversion, what could be used as an interrupt for a processor.