Servo Jitter – Resulting in a crash

I was recently flying my Tri in AUTO mode, flying a mission I had previously flown the day before, when to my horror it appeared to go completely nuts before free falling 100m to the ground. On review of the video from an onboard gopro you can clearly hear the yaw servo jittering before going crazy to the point that the  APM board went briefly into FailSafe mode then Disarmed in mid flight. ( not good )

I’ve been flying multirotors for a while now but have recently progressed / transitioned from a KK2 control board to the APM2.6. Over the last couple of months I’ve been working my way through the various flight modes and coming to terms with the seemingly endless functionality of Mission Planner.

Until now I’ve never had an issue with servo jitter ( on this setup or previous tricopers I’ve built ) so I’m a little confused as to just what might be causing the issue. So I guess what I’m looking for is a little guidance / wisdom on pining down the cause of the servo jitter. ( Having an unscheduled 100m free fall is not something I wish to repeat. )

Ive listed as much detail as I can on my current setup ( as it was on that day )


Frame: FliteTest – BatBone

Motors: NTM Prop Drive Series 28-26A 1200kv

ESC’s: HobbyKing 30A BlueSeries Brushless Speed Controller

Servo: Turnigy XGD-11MB Digital Mini Servo

Battery: Turnigy 2650mAh 4S 20C

Control Board:

 APM 2.6 Set Side Entry (external compass)

-3DR Radio Telemetry Kit - 915 Mhz


The power wiring is as per the documentation for using the Power Module and using power from one ESC to power the servo.


Power Module and using Servos with BEC power from one ESC

  • If you have a power module and you are using servos Remove JP1.
  • Provide APM and receiver power via the power module connected to the APM’s power module connector.
  • The BEC of a single ESC must provide sufficient power for all your servos.
  • When connecting your ESCs to the OUTPUT connector clip the BEC power leads on all but one of the ESC’s connectors.
  • Or connect only the ESC signal wires to the OUTPUT connector for all except one ESC.
  • And on that ESC connect all 3 wires to the OUTPUT connector.


I’ve included the log data from the APM and from the mission planner (as I had the telemetry link running at the time )

And a link to the gopro footage on youtube.

Many Thanks


2013-12-01 17-54-11.tlog

2013-12-04 20-31 27.log

2013-12-04 20-31 27.log.gpx

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  • It looks to me as if you had some sort of mechanical failure, like your ESC shorting. You mention it going into Failsafe, but the dataflash log doesn't show anything, no ERR entries. The data just stops high in the air.

    The attached plot of your altitude and voltage shows what was happening. Everything progresses well until about line 3969 where you are still at 14.51 volts. Then at line 4113, only 4 seconds later, you are at 13.65 volts. One second after that the data just ends. So something shorted out pretty substantially to bring your battery down like that. A look at your Current plot shows a big increase in current during that period too.

    Your Vcc doesn't look too bad to me which seems odd. Since you are powering your APM via a separate PM, even if the ESC blew, taking out power to the motors, power should remain to the APM. To me, this suggests a secondary failure in your main power wiring between the battery and the Power Module, possibly caused by a primary failure in your ESC. Perhaps your ESC blew and shorted, thus blowing out a weak solder joint near your battery?


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