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

Posted by Brian Christal on September 4, 2015 at 6:24am

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

Justin_Crash.gif

76_short8.zip

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Replies

  • Andre K. September 5, 2015 at 7:16am

    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 :)

    • Justin > Andre K. September 5, 2015 at 9:51pm

      So what would be the main cause of this?

      • Andre K. > Justin September 6, 2015 at 1:26am

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

        • Brian Christal > Andre K. September 6, 2015 at 4:56am

          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.

  • Andre K. September 4, 2015 at 11:00am

    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.

    • Brian Christal > Andre K. September 4, 2015 at 11:17am

      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

      • Andre K. > Brian Christal September 4, 2015 at 11:47am

        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...

        • Brian Christal > Andre K. September 4, 2015 at 12:03pm

          Is this the right graph to show the roll? Thanks! Brian
          3702797567?profile=original

          https://storage.ning.com/topology/rest/1.0/file/get/3702797567?profile=original
          • Andre K. > Brian Christal September 4, 2015 at 12:10pm

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

            • Brian Christal > Andre K. September 4, 2015 at 2:10pm

              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.3702885607?profile=original

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