Hints for crash analysis needed

I've got the problem described below and maybe you could give me some hints where to look for possible causes.

Frame: Quadcopter (many successful flights before modifying the camera gimbal)
Hardware: APM 2.5
Firmware: ArduCopter V3.1.5

Problems:
- Random, light twitches during flight
- Sudden altitude drop after a while in loiter mode
- Sudden roll to the left while hovering in stabilize mode, resulting in a crash

According to the information found here and the log, it could be a mechanical failure. I assume if I'd had a problem with a motor or an ESC, roll and pitch should show similar behavior in the log.

I'm also not sure if I can exclude a problem with the receiver or the PPM encoder.

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  • I've finally solved the problem and maybe this is helpful if you are experiencing sync issues with high-pole-count brushless motors.

    All my further testing lead to a sync issue of the motors (Turnigy Multistar 4220-650Kv + Afro 30A ESC) probably caused by higher weight and therefore higher current flow.
    I've tried different firmwares (SimonK, BLHeli) in various revisions with all kind of settings. Then I've tried different ESCs (Afro HV 20A, HobbyKing BlueSeries 30A) with no success. The sync issues remained and it looked like the motors were causing the problem. 

    In a last attempt I bought some Hobbywing Xrotor 20A Opto ESCs and without any further setup (except calibrating) the sync issue was gone.

  • T3
    Try changing the frame rate on your transmitter from 22ms to 11ms. Don't forget to rebind after you change the rate.
    • Thank you, Richard!

      One of the first things I've done was switching from 22 to 11 ms and I might be wrong but it felt like the twitches where still there. Then I switched back to 22ms and did all the above. So far it seems to work.

      Are there any downsides with the 11 ms frame rate?

      • T3
        Not that I'm aware of.
      • log RCIN first -   you should then see bad input. - I doubt RC is to blame.

        post full log if you want people to be able to help, and actually be able to base assumptions on something.

  • Thanks Andre!

    I've done the following and at least for the last two flights the problem was gone:
    - Disconnected and reconnected all the cables
    - Re-flashed the PPM encoder
    - Fixed the APM inside its case and re-mounted it with three layers of double sided tape
    - Re-routed some of the cables
    - Rebound the Spektrum receiver
    - Re-calibrated Radio, Accel and Compas in the Mission Planner

  • Log and check vibrations as well
This reply was deleted.

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