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MPU6050 IMU Calibration Guide

Overview

This guide explains how to calibrate the MPU6050 6-axis IMU (accelerometer and gyroscope) on the Wheelie robot. Proper calibration ensures accurate motion sensing, stable orientation, and reliable sensor fusion.

Why Calibrate?

  • Factory offsets: Each MPU6050 has unique bias and offset values.
  • Mounting orientation: Small misalignments affect readings.
  • Environmental factors: Temperature and vibration can introduce drift.

Prerequisites

  • Wheelie robot assembled with MPU6050 connected and powered.
  • Firmware flashed and serial monitor available (via PlatformIO or Arduino IDE).
  • Robot placed on a stable, level surface.

Calibration Steps

1. Prepare the Robot

  • Place the robot on a flat, stable surface.
  • Ensure the robot is completely still during calibration.

2. Start the Calibration Routine

  • Power on the robot and connect to the serial monitor (baud rate: 115200).
  • If your firmware includes a calibration mode, enter it (e.g., send calibrate_mpu via serial or use the CLI menu).
  • If not, modify your code to print raw accelerometer and gyroscope readings continuously.

3. Record Raw Readings

  • Observe the raw values for each axis (Accel X/Y/Z, Gyro X/Y/Z).
  • For a stationary, level robot:
    • Accelerometer Z should read close to +1g (typically ~16384 for ±2g setting).
    • Accelerometer X and Y should be near zero.
    • All gyroscope axes should be near zero.

4. Calculate Offsets

  • Accel Offset = 0 (X/Y), +1g (Z) - Raw Value
  • Gyro Offset = 0 - Raw Value
  • Average readings over several seconds for best results.

5. Update Firmware

  • In your code, subtract the calculated offsets from each raw reading:
// Example: Apply offsets in your read function
int16_t ax, ay, az, gx, gy, gz;
mpu.getMotion6(&ax, &ay, &az, &gx, &gy, &gz);
ax -= ACCEL_X_OFFSET;
ay -= ACCEL_Y_OFFSET;
az -= ACCEL_Z_OFFSET;
gx -= GYRO_X_OFFSET;
gy -= GYRO_Y_OFFSET;
gz -= GYRO_Z_OFFSET;
  • Store offsets in firmware or EEPROM for persistent calibration.

6. Validate Calibration

  • Re-test with the robot stationary and moving.
  • Confirm that stationary readings are close to expected values.
  • Adjust offsets if necessary.

Advanced: Using Calibration Libraries

Troubleshooting

  • Drifting values: Re-run calibration, check for vibration, or use digital low-pass filter.
  • Large offsets: Verify sensor orientation and mounting.
  • No response: Check I2C wiring and address.

References