David Grayson / Mbed 2 deprecated DeadReckoning

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@42:96671b71aac5, 2019-07-27 (annotated)

Committer:
DavidEGrayson
Date:
Sat Jul 27 20:58:46 2019 +0000
Revision:
42:96671b71aac5
Parent:
41:3ead1dd2cc3a
Child:
47:9773dc14c834
Calibrate L3G using a buffer of 1000 zero-rate readings.  Measured a drift of -1.850 degrees over 3 minutes (-0.01 degree per second).

Who changed what in which revision?

UserRevisionLine numberNew contents of line
DavidEGrayson 40:6fa672be85ec 1 #include "turn_sensor.h"
DavidEGrayson 40:6fa672be85ec 2 #include "l3g.h"
DavidEGrayson 40:6fa672be85ec 3
DavidEGrayson 40:6fa672be85ec 4 void TurnSensor::reset()
DavidEGrayson 40:6fa672be85ec 5 {
DavidEGrayson 40:6fa672be85ec 6 angleUnsigned = 0;
DavidEGrayson 40:6fa672be85ec 7 }
DavidEGrayson 40:6fa672be85ec 8
DavidEGrayson 40:6fa672be85ec 9 void TurnSensor::start()
DavidEGrayson 40:6fa672be85ec 10 {
DavidEGrayson 40:6fa672be85ec 11 timer.start();
DavidEGrayson 40:6fa672be85ec 12 rate = 0;
DavidEGrayson 40:6fa672be85ec 13 angleUnsigned = 0;
DavidEGrayson 40:6fa672be85ec 14 gyroLastUpdate = timer.read_us();
DavidEGrayson 40:6fa672be85ec 15 }
DavidEGrayson 40:6fa672be85ec 16
DavidEGrayson 40:6fa672be85ec 17 void TurnSensor::update()
DavidEGrayson 40:6fa672be85ec 18 {
DavidEGrayson 40:6fa672be85ec 19 if (l3gZAvailable() == 1)
DavidEGrayson 40:6fa672be85ec 20 {
DavidEGrayson 42:96671b71aac5 21 int32_t gz = l3gZReadCalibrated();
DavidEGrayson 40:6fa672be85ec 22 if (gz < -500000)
DavidEGrayson 40:6fa672be85ec 23 {
DavidEGrayson 40:6fa672be85ec 24 // error
DavidEGrayson 40:6fa672be85ec 25 return;
DavidEGrayson 42:96671b71aac5 26 }
DavidEGrayson 41:3ead1dd2cc3a 27
DavidEGrayson 40:6fa672be85ec 28 // The gyro on this robot is mounted upside down; account for that here so that
DavidEGrayson 40:6fa672be85ec 29 // we can have counter-clockwise be a positive rotation.
DavidEGrayson 41:3ead1dd2cc3a 30 gz = -gz;
DavidEGrayson 41:3ead1dd2cc3a 31
DavidEGrayson 40:6fa672be85ec 32 rate = gz;
DavidEGrayson 40:6fa672be85ec 33
DavidEGrayson 40:6fa672be85ec 34 // First figure out how much time has passed since the last update (dt)
DavidEGrayson 40:6fa672be85ec 35 uint16_t m = timer.read_us();
DavidEGrayson 40:6fa672be85ec 36 uint16_t dt = m - gyroLastUpdate;
DavidEGrayson 40:6fa672be85ec 37 gyroLastUpdate = m;
DavidEGrayson 40:6fa672be85ec 38
DavidEGrayson 40:6fa672be85ec 39 // Multiply dt by turnRate in order to get an estimation of how
DavidEGrayson 40:6fa672be85ec 40 // much the robot has turned since the last update.
DavidEGrayson 40:6fa672be85ec 41 // (angular change = angular velocity * time)
DavidEGrayson 40:6fa672be85ec 42 int32_t d = (int32_t)rate * dt;
DavidEGrayson 40:6fa672be85ec 43
DavidEGrayson 40:6fa672be85ec 44 // The units of d are gyro digits times microseconds. We need
DavidEGrayson 40:6fa672be85ec 45 // to convert those to the units of turnAngle, where 2^29 units
DavidEGrayson 40:6fa672be85ec 46 // represents 45 degrees. The conversion from gyro digits to
DavidEGrayson 40:6fa672be85ec 47 // degrees per second (dps) is determined by the sensitivity of
DavidEGrayson 40:6fa672be85ec 48 // the gyro: 0.07 degrees per second per digit.
DavidEGrayson 40:6fa672be85ec 49 //
DavidEGrayson 40:6fa672be85ec 50 // (0.07 dps/digit) * (1/1000000 s/us) * (2^29/45 unit/degree)
DavidEGrayson 40:6fa672be85ec 51 // = 14680064/17578125 unit/(digit*us)
DavidEGrayson 40:6fa672be85ec 52
DavidEGrayson 40:6fa672be85ec 53 angleUnsigned += (int64_t)d * 14680064 / 17578125;
DavidEGrayson 40:6fa672be85ec 54 }
DavidEGrayson 40:6fa672be85ec 55 }