David's dead reckoning code for the LVBots competition on March 6th. Uses the mbed LPC1768, DRV8835, QTR-3RC, and two DC motors with encoders.

Dependencies:   PololuEncoder Pacer mbed GeneralDebouncer

turn_sensor.cpp

Committer:
DavidEGrayson
Date:
18 months ago
Revision:
40:6fa672be85ec
Child:
41:3ead1dd2cc3a

File content as of revision 40:6fa672be85ec:

#include "turn_sensor.h"
#include "l3g.h"

void TurnSensor::reset()
{
    angleUnsigned = 0;
}

void TurnSensor::start()
{
    timer.start(); 
    rate = 0;  
    angleUnsigned = 0;
    gyroLastUpdate = timer.read_us();
}

void TurnSensor::update()
{
    if (l3gZAvailable() == 1)
    {
        int32_t gz = l3gZRead();
        if (gz < -500000)
        {
            // error
            return;
        }
        
        // The gyro on this robot is mounted upside down; account for that here so that
        // we can have counter-clockwise be a positive rotation.
        gz = -gz;
        
        rate = gz;
        
        // First figure out how much time has passed since the last update (dt)
        uint16_t m = timer.read_us();
        uint16_t dt = m - gyroLastUpdate;
        gyroLastUpdate = m;

        // Multiply dt by turnRate in order to get an estimation of how
        // much the robot has turned since the last update.
        // (angular change = angular velocity * time)
        int32_t d = (int32_t)rate * dt;

        // The units of d are gyro digits times microseconds.  We need
        // to convert those to the units of turnAngle, where 2^29 units
        // represents 45 degrees.  The conversion from gyro digits to
        // degrees per second (dps) is determined by the sensitivity of
        // the gyro: 0.07 degrees per second per digit.
        //
        // (0.07 dps/digit) * (1/1000000 s/us) * (2^29/45 unit/degree)
        // = 14680064/17578125 unit/(digit*us)
        //const float factor = (float)14680064 / 17578125;
        
        // Fudge factor to account for the fact that the gyro might be mounted
        // at a bad angle or it might be more or less sensitive than expected.
        //const float fudge = 0.98809906722;
        
        angleUnsigned += (int64_t)d * 14680064 / 17578125;
    }
}