Drone diving when going side to side


I’m having a recurring issue where my drone (built from the drone dojo’s pixhawk kit) apparently randomly tips over and dives to the ground. I would attach the log and a corresponding video, but new users are not allowed to upload files.

In this particular instance I am testing side to side motion and the error occurs while flying to the right and decelerating. The drone tips towards motor 3 and does not recover, diving to the ground. I find this especially strange considering this happens after several minutes of successful and controlled (although slow) flying.

Another error I am experiencing is that in alt hold or pos hold flight modes the drone tends to drift towards motor 3. Perhaps these errors are related, and motors 1 or 3 are unreliable?

Any help or suggestions would be greatly appreciated.


My initial thoughts are:
1 Motor 3 is defective, is binding because of debris, or rubbing against a set screw.
2 Motor 3 esc is defective or needs re-calibration.
3 There is asymmetric weight on the vehicle, ie, the center of mass is not centered
4 There is some intermittent and intolerable vibration that is feeding into the EKF causing strange flight behavior.
5 There is a problem with the Pixhawk IMU. Which ‘brand’ of Pixhawk are you using?

Granted these issues seem intermittent, but some suggestions -
1 Recalibrate everything
2 Switch Motor 3 with another motor and see the response.
3 Switch Motor 3 esc and see what happens.
4 Check all props are secure
5 Ensure Motor 3 spins freely
6 Ensure the original firmware was correct.

Drifting towards Motor 3 probably is related. My guess is the initial IMU calibration was not good. Those flight modes don’t rely on GPS, so that isn’t the issue.

Also, see this

You can also send me your .bin and video files to this address and I will take a look:

… jack