Apm 2.6 crash - Can't find out why

Hello community,

During my latest flight my quadcopter made several flips and crashed from 40 meters high. Reviewing the logs I couldn't understand which part is responsible for the crash. All parts were found in good condition. I mean the flight controller, ESCs, motors, Propellers etc. Only an arm broken and the landing gear. Lucky me but I am anxious about flying that thing again. So I could use some help.

My setup is:

Frame: Tarot 650 IronMan

Motors: 4x Sunnysky X4108S 480kv

ESCs : Turnigy Plush BlHeli Firmware 25A 

Propellers: Tarot 1555 Folding props

Flight controller: APM 2.6 clone

GPS: uBlox lea 6h

Battery: Turnigy 5000 4s 30C

Radio transmitter: Turnigy 9XR

Radio receiver: FrSky D8R-II PLUS 2.4Ghz 8CH


I have uploaded my log file if anyone needs it.

2016-02-17 15-12-28.log

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  • Are you sure that you have you checked all of your motors and ESCs?  You aren't logging RCOUT data which would show the PWM going to each motor which would be very helpful - but based upon your log the quad succeeded in maintaining Yaw control but was totally unable to maintain pitch and roll based Dest Pitch and Dest Roll.  At the time of the crash the throttle out also fluctuated wildly.  To me the quad behaved like it lost power to one of the motors.  

    Fair warning, I don't have a ton of experience - but I love going through log files to try to reconstruct crashes :) 

    • Sorry didn't see the previous reply before I posted. +1 on the "you lost a motor" theory.  I believe that's almost certainly what happened here.

      • After checking again I found that one connection of the front left motor's was loose and doesn't always give power to the motor. So I believe this is the problem and that it didn't happened from the impact. I have to solder those connections. Lesson taken. Thank you guys. You were both right!

        • That makes sense, I see that I wrote rear left by mistake, the graph supports with your findings.
  • near line 19300 you can clearly see how attitude and desired attitude diverts.

    this is a common example of what happens when you lose thust on one motor, - something went bad, may look like rear left arm of the quad, but I did not put a lot of thought to that.


    • Thanks for your answer. So do you believe that I should focus to the motors and escs?  The rear left arm is the only arm that broke during the incident. But I don't believe that it happened during the flight. Any ideas about that quick change of modes during the last seconds. As I remember I only change the mode to stabilize to save my day. But as I can see there 5 more mode changes.

      • On the mode change question the logs are pretty unambiguous.  You made 5 mode changes, or at least your board and receiver were pretty convinced you did.  That said, I don't think that made any difference - but the mode changes are expected given the inputs on Channel 5.  When your quad is crashing stress levels are pretty high, you probably fumbled with your switches.


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