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mbed Rover

Table of Contents

  1. Simple Rover
  2. PID Rover

http://mbed.org/media/uploads/aberk/_scaled_mbedrover.jpg

The mbed Rover is the result of combining the Stinger Robot Kit, the QEI, PID, and IMU libraries along with a ITG3200 gyroscope, ADXL345 accelerometer, and a pair of Polulu MD10B breakout boards driven by the Motor library.

Simple Rover

The simplest implementation involves driving the motors forward a set number of pulses as measured by the quadrature encoders. This involves no speed feedback from the motors and causes the rover to drift in different directions in a non-deterministic manner. If there was a bias to the direction of drift it would also be difficult to correct it with simply changing the speed of one wheel as we would most likely want to dynamically change the speed of the wheel throughout any movement (e.g. increase PWM signal at the beginning to overcome static friction, then decrease to a lower level).

Import program
SimpleRover - main.cpp

00001 /**
00002  * Drive a robot forwards or backwards by supplying a PWM signal to
00003  * H-bridges connected to the motors.
00004  */
00005 
00006 #include "Motor.h"
00007 #include "QEI.h"
00008 
00009 #define PULSES_PER_REVOLUTION 624
00010 
00011 Motor leftMotor(p21, p20, p19);  //pwm, inB, inA
00012 Motor rightMotor(p22, p17, p18); //pwm, inA, inB
00013 QEI leftQei(p29, p30, NC, 624);  //chanA, chanB, index, ppr
00014 QEI rightQei(p27, p28, NC, 624); //chanB, chanA, index, ppr
00015 
00016 int main() {
00017     
00018     leftMotor.period(0.00005);  //Set motor PWM periods to 20KHz.
00019     rightMotor.period(0.00005);
00020 
00021     int leftPulses  = 0;    //How far the left wheel has travelled.
00022     int rightPulses = 0;    //How far the right wheel has travelled.
00023     int distance    = 6000; //Number of pulses to travel.
00024 
00025     wait(5); //Wait a few seconds before we start moving.
00026     
00027     leftMotor.speed(0.4);
00028     rightMotor.speed(0.4);
00029     
00030     while((leftPulses < distance) || (rightPulses < distance)){
00031     
00032         leftPulses  = leftQei.getPulses();
00033         rightPulses = rightQei.getPulses();
00034         
00035     }
00036     
00037     leftMotor.brake();
00038     rightMotor.brake();
00039 
00040 }

PID Rover

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