Servo stutter

Hello everybody.

Me and my friend are trying to setup my T-Rex 600 with the APM 2.5 but we are having problems with the servos for roll and nick stuttering, but there is no issues when moving the Collective pitch. 

We have tried numerous things like, two BEC's, playing with reciever frame rate, different reciever/transmitter, older APM firmware, digital/analog servos ect. But it seem like the problem comes from the APM itself. 

What could be the problem? and what could fix this?

Video of the the problem in action: http://youtu.be/Htwj_53-4wo

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      • That log shows the problem in V3.1.5 in stab mode. The stuttering was also stil there in the Acro fix V3.1.3 but there were no stuttering in Acro mode.
  • Really? So it's not just a problem with the flybar mode.  That is odd then.  There must be something particular about your setup.

    Can you enable RCOut and PID logging.  Set Ch6 tuning to one of the Rate parameters.  This forces it to log Rate PID data.  Arm the copter so that it starts logging.  And then move the controls around enough to show this issue, and then post the log file here?

  • We are running the latest stable version. (the one you are given as standard, without changing to either "old" or beta.

    We have tried both flybar and flybarless mode same result. 

  • Yeah, I don't think that's right....  It is normal that with APM, the servo movements are slightly less smooth than you would normally get, but not like that!

    Which firmware is this?

    I assume you're using the Flybar mode?  Can you try Flybarless mode, and just see if the movement is better?

  • It seems that the problem is back in the newest firmware. (3.1.5)

  • Yes your point of interference is right, the collective should also be affected if that's the case.

    Maybe something is going wrong? There has been some issue with flybar mode in previous firmware version, the servos were not moving in acro mode. But as far as I remember this issue was already solved.

  • Thanks for the quick replies.

    We have tried to unplug the telemetry, that makes no difference and shouldn't the collective be having issues with interference aswell if that is the case? 

    I forgot to mention in the description that when we switch to Acro mode, non of the servos move. Which we also find strange.

  • Maybe try testing in Acro mode, which acts like a FBL unit and try again. If the swash is very smooth in this mode, then it's fine. There could be some disturbance coming from outside like radios, also unplug the telemetry and try again.

    As your collective is smooth, your APM is fine.

  • Its an original APM 2.5 that have been converted into a 2.6 by cutting the trace on the PCB. 

  • no that's not normal. I've never seen such stutering with my APM but it was on a 450 Trex, are you using the original APM?

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