Drone diving when going side to side

#1

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.

#2

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
https://dojofordrones.com/drone-flips-on-takeoff/

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

… jack