Uncommanded Pitch Runaway in Loiter


I'm running a DJI S900 on Pixhawk running the latest stable version with a frsky taranis. This morning I replaced the motor rubber dampening pads with DJI Part 35 which is a softer damper that is supposed to reduce vibration / micro bounces in the video. I had 3 successful flights and two near flyaway instances where full opposite input was insufficient to correct the drift while in loiter. Light Winds maybe 10mph at the time. 

I had two instances today where the copter in loiter began to drift primarily in the forward pitch direction where full opposite rc input would not override/correct the issue. In log 15-05-01-58-01 I was able to switch to stabilize and with full aft input on pitch was able to land successfully. Full input seemed to hold position rather than command a normal response in the intended direction

In log 15-05-01-21-00 I quickly switched to stabilize but do to height AGL impacted the ground prior to full recovery. 

I've attached a log from 15-04-27 as well which was prior to the change in motor damper rubber. From my eyes it looks like the vibration has decreased. I was assuming some bad vibrations where causing a severe drift in IMU but that doesn't seem to be the case. It doesn't appear the GPS wanders either. 

Any help to better understand will be greatly appreciated. 




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  • I have had issues like this many times.  Some I have associated with GPS signal loss.  I believe the arducopter does not well detect gps signal loss and respond as I would expect.  It will runaway.  I changed gps to a neo n8m, and get 2x the satellites, and no signal loss.  that has greatly improved that situation, though if I fly without paying attention to gps status, I can still get some unwanted erratic movement.  If you look at your TLM for satcount (not sure the exact naming), and watch for it to drop out, you can see if that is the problem.  Hope this helps.

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Shivchand Jaysaval liked Shivchand Jaysaval's profile
Aug 25