Pixracer IMU accelerometer bias constantly changing


We are using a pixracer on a 290 hexacopter, mostly running in offboard mode.

Our drones keep drifting position and losing altitude, so we noticed that the Accelerometer in the IMU has a large amount of bias. So, we recalibrate and note that the z-accelerometer is properly at -9.82 m/s/s.

However, the bias has been changing from the accelerometer, and we are unable to compensate for it. Sometimes the z-accelerometer will be -9.0, and other times -11.0. After recalibrating, we notice the same thing again.

Currently, the readings for each axis are: z is -10.6, y is 0.11, x is 0.06.

Z should clearly be 9.81, and both x and y should be 0.

The bias changes ever time we calibrate, and even during flight.

We’ve tried the thermal calibration, which had a minimal effect. We also tried writing our own z-controller, but since the bias constantly changes, it didn’t help. Lastly, this has happened on two drones so far, so we’re fairly sure that this isn’t a hardware issue.

Has anyone seen this before? Any ideas would be appreciated :slight_smile:

Thanks in advance!

Can you share logs? http://logs.px4.io/

Logs with and without thermal calibration would be interesting to compare.