Unable to get raw accelerometer data after calculating quaternion

[lannerxiii]

Hello, I am facing a problem getting raw accelerometer data. I need to substract the gravity from my raw accel data,so I am calculating my quaternions with DPM. My code is the following

  float q0 = imu.calcQuat(imu.qw);
  float q1 = imu.calcQuat(imu.qx);
  float q2 = imu.calcQuat(imu.qy);
  float q3 = imu.calcQuat(imu.qz);

  Serial.println("Q: " + String(q0, 4) + ", " + String(q1, 4) + ", " + String(q2, 4) + ", " + String(q3, 4));
  float g0,g1,g2 = 0;

  g0 = 2 * (q1 * q3 - q0 * q2);
  g1 = 2 * (q0 * q1 - q2 * q3);
  g2 = q0 * q0 - q1 * q1 - q2 * q2 + q3 * q3;

  ax =  imu.calcAccel(imu.ay);
  ay =  imu.calcAccel(imu.ay);
  az =  imu.calcAccel(imu.az);

  cax =  (9.8 * ax - g0);
  cay =  (9.8 * ay - g1);
  caz =  (9.8 * az - g2);
  Serial.println("A: " + String(g0, 4) + ", " + String(g1, 4) + ", " + String(g2, 4) );

Im using the DPM Quaternion example and made those modifications, but my ax, ay and Az values are zero. The main loop it's exactly the one from the example, I only removed the call to computeEulerAngles() because I do not need it. I think Im not understanding exactly how to get the raw data, because the basic example is different, also I know understand that the dpm code utilizes a FIFO Buffer to store the data. I need to get the raw AY,AY and AZ values that were used to calculate the quaternion. Am I doing something wrong?

Thank you

[cristian1706]

I am with the same problem... if anyone could help us I would appreciate it

[beegee-tokyo]

I got it to work with both DMP FiFo AND mag values by initializing like this:

if (imu.begin() != INV_SUCCESS)
{
    while (1)
    {
        Serial.println("Unable to communicate with MPU-9250");
        Serial.println("Check connections, and try again.");
        Serial.println();
        delay(5000);
    }
}

imu.dmpBegin(DMP_FEATURE_6X_LP_QUAT |         // Enable 6-axis quat
                 DMP_FEATURE_GYRO_CAL |       // Use gyro calibration
                 DMP_FEATURE_SEND_RAW_ACCEL | // Send raw accelerometer values to FIFO
                 DMP_FEATURE_SEND_RAW_GYRO,   // Send raw gyroscope values to FIFO
                 10);                             // Set DMP FIFO rate to 10 Hz

// Enable all sensors:
imu.setSensors(INV_XYZ_GYRO | INV_XYZ_ACCEL | INV_XYZ_COMPASS);

// Likewise, the compass (magnetometer) sample rate can be
// set using the setCompassSampleRate() function.
// This value can range between: 1-100Hz
imu.setCompassSampleRate(10); // Set mag rate to 10Hz

and then in my loop I read the data like this

if (imu.dataReady())
{
    imu.update(UPDATE_COMPASS);
}

// Check for new data in the FIFO
if (imu.fifoAvailable())
{
    // Use dmpUpdateFifo to update the ax, gx, mx, etc. values
    if (imu.dmpUpdateFifo() == INV_SUCCESS)
    {
        // computeEulerAngles can be used -- after updating the
        // quaternion values -- to estimate roll, pitch, and yaw
        imu.computeEulerAngles();
    }
}
Serial.printf("FLOAT:\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\n",
              imu.calcAccel(imu.ax), imu.calcAccel(imu.ay), imu.calcAccel(imu.az),
              imu.calcGyro(imu.gx), imu.calcGyro(imu.gy), imu.calcGyro(imu.gz),
              imu.calcMag(imu.mx), imu.calcMag(imu.my), imu.calcMag(imu.mz));
Serial.printf("Roll: %.2f\tPitch: %.2f\tYaw: %.2f\n",
              imu.roll,
              imu.pitch,
              imu.yaw);

[cristian1706]

I got it to work with both DMP FiFo AND mag values by initializing like this:

if (imu.begin() != INV_SUCCESS)
{
  while (1)
  {
      Serial.println("Unable to communicate with MPU-9250");
      Serial.println("Check connections, and try again.");
      Serial.println();
      delay(5000);
  }
}

imu.dmpBegin(DMP_FEATURE_6X_LP_QUAT |       // Enable 6-axis quat
               DMP_FEATURE_GYRO_CAL |       // Use gyro calibration
               DMP_FEATURE_SEND_RAW_ACCEL | // Send raw accelerometer values to FIFO
               DMP_FEATURE_SEND_RAW_GYRO,   // Send raw gyroscope values to FIFO
               10);                             // Set DMP FIFO rate to 10 Hz

// Enable all sensors:
imu.setSensors(INV_XYZ_GYRO | INV_XYZ_ACCEL | INV_XYZ_COMPASS);

// Likewise, the compass (magnetometer) sample rate can be
// set using the setCompassSampleRate() function.
// This value can range between: 1-100Hz
imu.setCompassSampleRate(10); // Set mag rate to 10Hz

and then in my loop I read the data like this

if (imu.dataReady())
{
  imu.update(UPDATE_COMPASS);
}

// Check for new data in the FIFO
if (imu.fifoAvailable())
{
  // Use dmpUpdateFifo to update the ax, gx, mx, etc. values
  if (imu.dmpUpdateFifo() == INV_SUCCESS)
  {
      // computeEulerAngles can be used -- after updating the
      // quaternion values -- to estimate roll, pitch, and yaw
      imu.computeEulerAngles();
  }
}
Serial.printf("FLOAT:\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\t%.2f\n",
            imu.calcAccel(imu.ax), imu.calcAccel(imu.ay), imu.calcAccel(imu.az),
            imu.calcGyro(imu.gx), imu.calcGyro(imu.gy), imu.calcGyro(imu.gz),
            imu.calcMag(imu.mx), imu.calcMag(imu.my), imu.calcMag(imu.mz));
Serial.printf("Roll: %.2f\tPitch: %.2f\tYaw: %.2f\n",
            imu.roll,
            imu.pitch,
            imu.yaw);

Thank you very much, I will be testing this soon! :D

[beegee-tokyo]

Weird. My above solution worked perfectly with a nRF52832 Feather board and a ESP32 Feather board, but fails on my custom board with an Insight ISP4520 (Nordic nRF52832 + Semtech SX1262 LoRa transceiver). Still investigating.

[cristian1706]

Weird. My above solution worked perfectly with a nRF52832 Feather board and a ESP32 Feather board, but fails on my custom board with an Insight ISP4520 (Nordic nRF52832 + Semtech SX1262 LoRa transceiver). Still investigating.

Thanks! Please let me know