ArduPlane crash - Log looks good - Can't find reason for crash

Please see attached log and screenshot.

  • Pixhawk
  • Flying wing
  • Arduplane 3.3

Flying mission with auto takeoff and waypoints. Plane perfectly executes take off and heads to first waypoint. Upon arrival at first waypoint plane pitches down until impact - even though desired pitch is up. No failsafes. No errors I can find. Z vibration low at time of failure. Any ideas?

Thanks!

-Brian

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look at the crazy uncommanded roll you have after log line 47600 , it banks over for no reason (RCOU.ch1 & ch2) does nothing to cause that - it tried to roll back later, but is unable,

most likely a control link fell apart or loose control surface.

Thank you Andre for the excellent analysis. I suspected mechanical failure. Please help me understand how you see the uncommanded roll in the log?

Thanks!

Brian

I see a rapid roll (before you loose altitude) , your RCIN tels me it's not manually commanded, at the same time i see  RCOUT.ch1  RCOUT.ch2 (your elevons servo signal) does not deviate from "normal"

- then, as you got big roll angle, you can see autopilot try to correct the roll with very big servo output (compared to usual flight till then), but it does not help...

Is this the right graph to show the roll? Thanks! Brian

I've been using ATT.Roll , but it'do.

Sorry to beat a dead horse, but I don't see the uncommanded roll. Roll and Desired Roll are somewhat aligned. Pitch and Desired Pitch clearly diverge.

yes, sorry for that , too quick look - you are right, pitch

by line 52650 roll deviates a lot as well.

The only thing I think is strange, did your mission had only 4 commands ?  -  was it a test mission (it seems so)

The plane crashed in a field and rested over night with power on. Amazingly the lipo powered without completely discharging and damaging the battery. The Log file was 389 MB so I deleted the part where the plane was just sitting. The plane was still together and flyable. The servos, hinges, pushrods, control horns, are all still good. This seems like a mechanical problem, but I can't find it.

regarding your PM:

Yes, DesRoll  & roll matches at line 48827 , but watch from ~49000  your roll does no longer follow and pitch starts dropping too.

It was late yesterday - it seems i were reading wrong lines, at time - must stop working too much on things :)

So what would be the main cause of this?

any problem that may cause contol surface(s) not move accordingly to PWM output. , wiring, servo power, servo, etc..

Can you see PWM commands in the log? The plane is still intact after the crash. It is a flying wing. Both elevon servos and control linkages are good. Seems like something was lost between Pixhawk Desired Pitch Up and the servo. Also, since it's a flying wing the plane will spiral down if you lose a servo. Can you tell from the log if the plane is spiraling? Seems like the log would show an oscillation. I will take a plane out later today and send it down in a spiral in stabilize mode and see.

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