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zr-v4/libraries/DCM/DCM.cpp

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#include "DCM.h"
// XXX HACKS
APM_ADC adc;
// XXX END HACKS
#define GRAVITY 418 //this equivalent to 1G in the raw data coming from the accelerometer
#define ADC_CONSTRAINT 900
#define Kp_ROLLPITCH 0.0014 //0.015 // Pitch&Roll Proportional Gain
#define Ki_ROLLPITCH 0.0000003 // 0.00001 Pitch&Roll Integrator Gain
#define Kp_YAW 1.2 // 1.2 Yaw Porportional Gain
#define Ki_YAW 0.00005 // 0.00005 Yaw Integrator Gain
// Sensor: GYROX, GYROY, GYROZ, ACCELX, ACCELY, ACCELZ
const uint8_t AP_DCM::_sensors[6] = {1,2,0,4,5,6}; // For ArduPilot Mega Sensor Shield Hardware
const int AP_DCM::_sensor_signs[] = {1,-1,-1,-1,1,1,-1,-1,-1}; //{-1,1,-1,1,-1,1,-1,-1,-1} !!!! These are probably not right
// Temp compensation curve constants
// These must be produced by measuring data and curve fitting
// [X/Y/Z gyro][A/B/C or 0 order/1st order/2nd order constants]
const float AP_DCM::_gyro_temp_curve[3][3] = {
{1665,0,0},
{1665,0,0},
{1665,0,0}
}; // values may migrate to a Config file
// Constructors ////////////////////////////////////////////////////////////////
AP_DCM::AP_DCM(APM_Compass *withCompass) :
_compass(withCompass),
_dcm_matrix(1, 0, 0,
0, 1, 0,
0, 0, 1),
_G_Dt(0.02),
_course_over_ground_x(0),
_course_over_ground_y(1)
{
}
void
AP_DCM::update_DCM(void)
{
read_adc_raw(); // Get current values for IMU sensors
matrix_update(); // Integrate the DCM matrix
normalize(); // Normalize the DCM matrix
drift_correction(); // Perform drift correction
euler_angles(); // Calculate pitch, roll, yaw for stabilization and navigation
}
// Read the 6 ADC channels needed for the IMU
// ------------------------------------------
void
AP_DCM::read_adc_raw(void)
{
int tc_temp = adc.Ch(_gyro_temp_ch);
for (int i = 0; i < 6; i++) {
_adc_in[i] = adc.Ch(_sensors[i]);
if (i < 3) { // XXX magic numbers!
_adc_in[i] -= _gyro_temp_comp(i, tc_temp); // Subtract temp compensated typical gyro bias
} else {
_adc_in[i] -= 2025; // Subtract typical accel bias
}
}
}
// Returns the temperature compensated raw gyro value
//---------------------------------------------------
float
AP_DCM::_gyro_temp_comp(int i, int temp) const
{
// We use a 2nd order curve of the form Gtc = A + B * Graw + C * (Graw)**2
//------------------------------------------------------------------------
return _gyro_temp_curve[i][0] + _gyro_temp_curve[i][1] * temp + _gyro_temp_curve[i][2] * temp * temp;
}
// Returns an analog value with the offset removed
// -----------------
float
AP_DCM::read_adc(int select)
{
float temp;
if (_sensor_signs[select] < 0)
temp = (_adc_offset[select] - _adc_in[select]);
else
temp = (_adc_in[select] - _adc_offset[select]);
if (abs(temp) > ADC_CONSTRAINT)
adc_constraints++; // We keep track of the number of times we constrain the ADC output for performance reporting
/*
// For checking the pitch/roll drift correction gain time constants
switch (select) {
case 3:
return 0;
break;
case 4:
return 0;
break;
case 5:
return 400;
break;
}
*/
//End of drift correction gain test code
return constrain(temp, -ADC_CONSTRAINT, ADC_CONSTRAINT); // Throw out nonsensical values
}
/**************************************************/
void
AP_DCM::normalize(void)
{
float error = 0;
DCM_Vector temporary[3];
uint8_t problem = 0;
error = -_dcm_matrix(0).dot_product(_dcm_matrix(1)) * 0.5; // eq.19
temporary[0] = _dcm_matrix(1) * error + _dcm_matrix(0); // eq.19
temporary[1] = _dcm_matrix(0) * error + _dcm_matrix(1); // eq.19
temporary[2] = temporary[0] ^ temporary[1]; // c= a x b // eq.20
_dcm_matrix(0) = _renorm(temporary[0], problem);
_dcm_matrix(1) = _renorm(temporary[1], problem);
_dcm_matrix(2) = _renorm(temporary[2], problem);
if (problem == 1) { // Our solution is blowing up and we will force back to initial condition. Hope we are not upside down!
_dcm_matrix(0, 0)= 1.0f;
_dcm_matrix(0, 1)= 0.0f;
_dcm_matrix(0, 2)= 0.0f;
_dcm_matrix(1, 0)= 0.0f;
_dcm_matrix(1, 1)= 1.0f;
_dcm_matrix(1, 2)= 0.0f;
_dcm_matrix(2, 0)= 0.0f;
_dcm_matrix(2, 1)= 0.0f;
_dcm_matrix(2, 2)= 1.0f;
}
}
DCM_Vector
AP_DCM::_renorm(DCM_Vector const &a, uint8_t &problem)
{
float renorm;
renorm = a.dot_product(a);
if (renorm < 1.5625f && renorm > 0.64f) { // Check if we are OK with Taylor expansion
renorm = 0.5 * (3 - renorm); // eq.21
} else if (renorm < 100.0f && renorm > 0.01f) {
renorm = 1.0 / sqrt(renorm);
renorm_sqrt_count++;
} else {
problem = 1;
renorm_blowup_count++;
}
return(a * renorm);
}
/**************************************************/
void
AP_DCM::drift_correction(void)
{
//Compensation the Roll, Pitch and Yaw drift.
float mag_heading_x;
float mag_heading_y;
float error_course = 0;
static float scaled_omega_P[3];
static float scaled_omega_I[3];
float accel_magnitude;
float accel_weight;
float integrator_magnitude;
//*****Roll and Pitch***************
// Calculate the magnitude of the accelerometer vector
accel_magnitude = _accel_vector.magnitude() / GRAVITY; // Scale to gravity.
// Dynamic weighting of accelerometer info (reliability filter)
// Weight for accelerometer info (<0.5G = 0.0, 1G = 1.0 , >1.5G = 0.0)
accel_weight = constrain(1 - 2 * abs(1 - accel_magnitude), 0, 1); //
// We monitor the amount that the accelerometer based drift correction is deweighted for performanc reporting
imu_health = imu_health + 0.02 * (accel_weight-.5);
imu_health = constrain(imu_health, 0, 1);
// adjust the ground of reference
_error_roll_pitch = _accel_vector ^ _dcm_matrix(2);
// error_roll_pitch are in Accel ADC units
// Limit max error_roll_pitch to limit max omega_P and omega_I
_error_roll_pitch(0) = constrain(_error_roll_pitch(0), -50, 50);
_error_roll_pitch(1) = constrain(_error_roll_pitch(1), -50, 50);
_error_roll_pitch(2) = constrain(_error_roll_pitch(2), -50, 50);
_omega_P = _error_roll_pitch * (Kp_ROLLPITCH * accel_weight);
_omega_I += _error_roll_pitch * (Ki_ROLLPITCH * accel_weight);
//*****YAW***************
if (_compass) {
// We make the gyro YAW drift correction based on compass magnetic heading
error_course= (_dcm_matrix(0, 0) * _compass->Heading_Y) - (_dcm_matrix(1, 0) * _compass->Heading_X); // Calculating YAW error
} else {
// Use GPS Ground course to correct yaw gyro drift
if (ground_speed >= SPEEDFILT) {
// Optimization: We have precalculated course_over_ground_x and course_over_ground_y (Course over Ground X and Y) from GPS info
error_course = (_dcm_matrix(0, 0) * _course_over_ground_y) - (_dcm_matrix(1, 0) * _course_over_ground_x); // Calculating YAW error
}
}
_error_yaw = _dcm_matrix(2) * error_course; // Applys the yaw correction to the XYZ rotation of the aircraft, depeding the position.
_omega_P += _error_yaw * Kp_YAW; // Adding Proportional.
_omega_I += _error_yaw * Ki_YAW; // adding integrator to the omega_I
// Here we will place a limit on the integrator so that the integrator cannot ever exceed half the saturation limit of the gyros
integrator_magnitude = sqrt(_omega_I.dot_product(_omega_I));
if (integrator_magnitude > radians(300)) {
_omega_I *= (0.5f * radians(300) / integrator_magnitude);
}
}
/**************************************************/
void
AP_DCM::_accel_adjust(void)
{
_accel_vector(1) += accel_scale((ground_speed / 100) * _omega(2)); // Centrifugal force on Acc_y = GPS_speed * GyroZ
_accel_vector(2) -= accel_scale((ground_speed / 100) * _omega(1)); // Centrifugal force on Acc_z = GPS_speed * GyroY
}
/**************************************************/
void
AP_DCM::matrix_update(void)
{
DCM_Matrix update_matrix;
_gyro_vector(0) = gyro_scaled_X(read_adc(0)); // gyro x roll
_gyro_vector(1) = gyro_scaled_Y(read_adc(1)); // gyro y pitch
_gyro_vector(2) = gyro_scaled_Z(read_adc(2)); // gyro Z yaw
//Record when you saturate any of the gyros.
if((abs(_gyro_vector(0)) >= radians(300)) ||
(abs(_gyro_vector(1)) >= radians(300)) ||
(abs(_gyro_vector(2)) >= radians(300)))
gyro_sat_count++;
/*
Serial.print (__adc_in[0]);
Serial.print (" ");
Serial.print (_adc_offset[0]);
Serial.print (" ");
Serial.print (_gyro_vector(0));
Serial.print (" ");
Serial.print (__adc_in[1]);
Serial.print (" ");
Serial.print (_adc_offset[1]);
Serial.print (" ");
Serial.print (_gyro_vector(1));
Serial.print (" ");
Serial.print (__adc_in[2]);
Serial.print (" ");
Serial.print (_adc_offset[2]);
Serial.print (" ");
Serial.println (_gyro_vector(2));
*/
// _accel_vector(0) = read_adc(3); // acc x
// _accel_vector(1) = read_adc(4); // acc y
// _accel_vector(2) = read_adc(5); // acc z
// Low pass filter on accelerometer data (to filter vibrations)
_accel_vector(0) = _accel_vector(0) * 0.6 + (float)read_adc(3) * 0.4; // acc x
_accel_vector(1) = _accel_vector(1) * 0.6 + (float)read_adc(4) * 0.4; // acc y
_accel_vector(2) = _accel_vector(2) * 0.6 + (float)read_adc(5) * 0.4; // acc z
_omega = _gyro_vector + _omega_I; // adding proportional term
_omega_vector = _omega + _omega_P; // adding Integrator term
_accel_adjust(); // Remove centrifugal acceleration.
#if OUTPUTMODE == 1
update_matrix(0, 0) = 0;
update_matrix(0, 1) = -_G_Dt * _omega_vector(2); // -z
update_matrix(0, 2) = _G_Dt * _omega_vector(1); // y
update_matrix(1, 0) = _G_Dt * _omega_vector(2); // z
update_matrix(1, 1) = 0;
update_matrix(1, 2) = -_G_Dt * _omega_vector(0); // -x
update_matrix(2, 0) = -_G_Dt * _omega_vector(1); // -y
update_matrix(2, 1) = _G_Dt * _omega_vector(0); // x
update_matrix(2, 2) = 0;
#else // Uncorrected data (no drift correction)
update_matrix(0, 0) = 0;
update_matrix(0, 1) = -_G_Dt * _gyro_vector(2); // -z
update_matrix(0, 2) = _G_Dt * _gyro_vector(1); // y
update_matrix(1, 0) = _G_Dt * _gyro_vector(2); // z
update_matrix(1, 1) = 0;
update_matrix(1, 2) = -_G_Dt * _gyro_vector(0);
update_matrix(2, 0) = -_G_Dt * _gyro_vector(1);
update_matrix(2, 1) = _G_Dt * _gyro_vector(0);
update_matrix(2, 2) = 0;
#endif
// update
_dcm_matrix += _dcm_matrix * update_matrix;
/*
Serial.print (_G_Dt * 1000);
Serial.print (" ");
Serial.print (dcm_matrix(0, 0));
Serial.print (" ");
Serial.print (dcm_matrix(0, 1));
Serial.print (" ");
Serial.print (dcm_matrix(0, 2));
Serial.print (" ");
Serial.print (dcm_matrix(1, 0));
Serial.print (" ");
Serial.print (dcm_matrix(1, 1));
Serial.print (" ");
Serial.print (dcm_matrix(1, 2));
Serial.print (" ");
Serial.print (dcm_matrix(2, 0));
Serial.print (" ");
Serial.print (dcm_matrix(2, 1));
Serial.print (" ");
Serial.println (dcm_matrix(2, 2));
*/
}
/**************************************************/
void
AP_DCM::euler_angles(void)
{
#if (OUTPUTMODE == 2) // Only accelerometer info (debugging purposes)
roll = atan2(_accel_vector(1), _accel_vector(2)); // atan2(acc_y, acc_z)
roll_sensor = degrees(roll) * 100;
pitch = -asin((_accel_vector(0)) / (double)GRAVITY); // asin(acc_x)
pitch_sensor = degrees(pitch) * 100;
yaw = 0;
#else
pitch = -asin(_dcm_matrix(2, 0));
pitch_sensor = degrees(pitch) * 100;
roll = atan2(_dcm_matrix(2, 1), _dcm_matrix(2, 2));
roll_sensor = degrees(roll) * 100;
yaw = atan2(_dcm_matrix(1, 0), _dcm_matrix(0, 0));
yaw_sensor = degrees(yaw) * 100;
#endif
/*
Serial.print ("Roll ");
Serial.print (roll_sensor / 100);
Serial.print (", Pitch ");
Serial.print (pitch_sensor / 100);
Serial.print (", Yaw ");
Serial.println (yaw_sensor / 100);
*/
}
/**************************************************/
//Computes the dot product of two vectors
float
DCM_Vector::dot_product(DCM_Vector const &vector2) const
{
float op = 0;
for(int c = 0; c < 3; c++)
op += _v[c] * vector2(c);
return op;
}
// cross-product
DCM_Vector
DCM_Vector::operator^(DCM_Vector const &a) const
{
DCM_Vector result;
result(0) = (_v[1] * a(2)) - (_v[2] * a(1));
result(1) = (_v[2] * a(0)) - (_v[0] * a(2));
result(2) = (_v[0] * a(1)) - (_v[1] * a(0));
return(result);
}
// scale
DCM_Vector
DCM_Vector::operator*(float scale) const
{
DCM_Vector result;
result(0) = _v[0] * scale;
result(1) = _v[1] * scale;
result(2) = _v[2] * scale;
return(result);
}
// scale
void
DCM_Vector::operator*=(float scale)
{
_v[0] *= scale;
_v[1] *= scale;
_v[2] *= scale;
}
// add
DCM_Vector
DCM_Vector::operator+(DCM_Vector const &a) const
{
DCM_Vector result;
result(0) = _v[0] + a(0);
result(1) = _v[1] + a(1);
result(2) = _v[2] + a(2);
return(result);
}
// add
void
DCM_Vector::operator+=(DCM_Vector const &a)
{
_v[0] += a(0);
_v[1] += a(1);
_v[2] += a(2);
}
// magnitude
float
DCM_Vector::magnitude(void) const
{
return(sqrt((_v[0] * _v[0]) +
(_v[1] * _v[1]) +
(_v[2] * _v[2])));
}
// 3x3 matrix multiply
DCM_Matrix
DCM_Matrix::operator*(DCM_Matrix const &a) const
{
DCM_Matrix result;
for (int x = 0; x < 3; x++) {
for (int y = 0; y < 3; y++) {
result(x, y) =
_m[x](0) * a(0, y) +
_m[x](1) * a(1, y) +
_m[x](2) * a(2, y);
}
}
return(result);
}
// 3x3 matrix add
void
DCM_Matrix::operator+=(DCM_Matrix const &a)
{
for (int x = 0; x < 3; x++)
for (int y = 0; y < 3; y++)
_m[x](y) += a(x,y);
}