ardupilot/Arducopter/DCM.pde

/* ******* ADC functions ********************* */
// Read all the ADC channles
void Read_adc_raw(void)
{
  int temp;
  
  for (int i=0;i<6;i++)
    AN[i] = APM_ADC.Ch(sensors[i]);
  
  // Correction for non ratiometric sensor (test code)
  //temp = APM_ADC.Ch(3);
  //AN[0] += 1500-temp;
  //AN[1] += 1500-temp;
  //AN[2] += 1500-temp;
}

// Returns an analog value with the offset
int read_adc(int select)
{
  if (SENSOR_SIGN[select]<0)
    return (AN_OFFSET[select]-AN[select]);
  else
    return (AN[select]-AN_OFFSET[select]);
}
/* ******************************************* */

/* ******* DCM IMU functions ********************* */
/**************************************************/
void Normalize(void)
{
  float error=0;
  float temporary[3][3];
  float renorm=0;
  
  error= -Vector_Dot_Product(&DCM_Matrix[0][0],&DCM_Matrix[1][0])*.5; //eq.19

  Vector_Scale(&temporary[0][0], &DCM_Matrix[1][0], error); //eq.19
  Vector_Scale(&temporary[1][0], &DCM_Matrix[0][0], error); //eq.19
  
  Vector_Add(&temporary[0][0], &temporary[0][0], &DCM_Matrix[0][0]);//eq.19
  Vector_Add(&temporary[1][0], &temporary[1][0], &DCM_Matrix[1][0]);//eq.19
  
  Vector_Cross_Product(&temporary[2][0],&temporary[0][0],&temporary[1][0]); // c= a x b //eq.20
  
  renorm= .5 *(3 - Vector_Dot_Product(&temporary[0][0],&temporary[0][0])); //eq.21
  Vector_Scale(&DCM_Matrix[0][0], &temporary[0][0], renorm);
  
  renorm= .5 *(3 - Vector_Dot_Product(&temporary[1][0],&temporary[1][0])); //eq.21
  Vector_Scale(&DCM_Matrix[1][0], &temporary[1][0], renorm);
  
  renorm= .5 *(3 - Vector_Dot_Product(&temporary[2][0],&temporary[2][0])); //eq.21
  Vector_Scale(&DCM_Matrix[2][0], &temporary[2][0], renorm);
}

/**************************************************/
void Drift_correction(void)
{
  //Compensation the Roll, Pitch and Yaw drift. 
  float errorCourse;
  static float Scaled_Omega_P[3];
  static float Scaled_Omega_I[3];
  float Accel_magnitude;
  float Accel_weight;
  
  //*****Roll and Pitch***************

  // Calculate the magnitude of the accelerometer vector
  //Accel_magnitude = sqrt(Accel_Vector[0]*Accel_Vector[0] + Accel_Vector[1]*Accel_Vector[1] + Accel_Vector[2]*Accel_Vector[2]);
  //Accel_magnitude = Accel_magnitude / GRAVITY; // Scale to gravity.
  // Weight for accelerometer info (<0.75G = 0.0, 1G = 1.0 , >1.25G = 0.0)
  // Accel_weight = constrain(1 - 4*abs(1 - Accel_magnitude),0,1);
  // 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);
  Accel_weight = 1.0;

  Vector_Cross_Product(&errorRollPitch[0],&Accel_Vector[0],&DCM_Matrix[2][0]); //adjust the ground of reference
  Vector_Scale(&Omega_P[0],&errorRollPitch[0],Kp_ROLLPITCH*Accel_weight);
  
  Vector_Scale(&Scaled_Omega_I[0],&errorRollPitch[0],Ki_ROLLPITCH*Accel_weight);
  Vector_Add(Omega_I,Omega_I,Scaled_Omega_I);
  
  //*****YAW***************
  // We make the gyro YAW drift correction based on compass magnetic heading 
  if (MAGNETOMETER == 1) {
    errorCourse= (DCM_Matrix[0][0]*APM_Compass.Heading_Y) - (DCM_Matrix[1][0]*APM_Compass.Heading_X);  //Calculating YAW error
    Vector_Scale(errorYaw,&DCM_Matrix[2][0],errorCourse); //Applys the yaw correction to the XYZ rotation of the aircraft, depeding the position.
  
    Vector_Scale(&Scaled_Omega_P[0],&errorYaw[0],Kp_YAW);
    Vector_Add(Omega_P,Omega_P,Scaled_Omega_P);//Adding  Proportional.
  
    Vector_Scale(&Scaled_Omega_I[0],&errorYaw[0],Ki_YAW);
    Vector_Add(Omega_I,Omega_I,Scaled_Omega_I);//adding integrator to the Omega_I
  }

}
/**************************************************/
void Accel_adjust(void)
{
  //Accel_Vector[1] += Accel_Scale(speed_3d*Omega[2]);  // Centrifugal force on Acc_y = GPS_speed*GyroZ
  //Accel_Vector[2] -= Accel_Scale(speed_3d*Omega[1]);  // Centrifugal force on Acc_z = GPS_speed*GyroY
}
/**************************************************/

void Matrix_update(void)
{
  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
  
  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]*0.5 + (float)read_adc(3)*0.5; // acc x
  //Accel_Vector[1]=Accel_Vector[1]*0.5 + (float)read_adc(4)*0.5; // acc y
  //Accel_Vector[2]=Accel_Vector[2]*0.5 + (float)read_adc(5)*0.5; // acc z
  
  Vector_Add(&Omega[0], &Gyro_Vector[0], &Omega_I[0]);//adding integrator
  Vector_Add(&Omega_Vector[0], &Omega[0], &Omega_P[0]);//adding proportional
  
  //Accel_adjust();//adjusting centrifugal acceleration. // Not used for quadcopter
  
 #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;
  #endif
  #if OUTPUTMODE==0
  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

  Matrix_Multiply(DCM_Matrix,Update_Matrix,Temporary_Matrix); //a*b=c

  for(int x=0; x<3; x++)  //Matrix Addition (update)
  {
    for(int y=0; y<3; y++)
    {
      DCM_Matrix[x][y]+=Temporary_Matrix[x][y];
    } 
  }
}

void Euler_angles(void)
{
  #if (OUTPUTMODE==2)         // Only accelerometer info (debugging purposes)
    roll = atan2(Accel_Vector[1],Accel_Vector[2]);   // atan2(acc_y,acc_z)
    pitch = -asin((Accel_Vector[0])/(float)GRAVITY); // asin(acc_x)
    yaw = 0;
  #else        // Euler angles from DCM matrix
    pitch = asin(-DCM_Matrix[2][0]);
    roll = atan2(DCM_Matrix[2][1],DCM_Matrix[2][2]);
    yaw = atan2(DCM_Matrix[1][0],DCM_Matrix[0][0]);
  #endif
}