Unexpected yaw

I'm having an issue where the copter frequently yaws unexpectedly.  I believe the copter is accurately controlling it's yaw, so the yaw movement is being generated somewhere within the control system.  I've checked that my RC Rudder input is centered, and I've checked (though it seems like this is still the most likely problem) that my compass orientation is correct.

Can anyone take a look at my log files and figure out what's going on?  I've attached log files of two flights where this issue occurred.

Here's an image showing centered RC Rudder input, but both desired yaw and actual yaw moving steadily (towards the end of the graph):


The copter is built so that the Pixhawk is right-side-up but facing the back of the copter.  The GPS/Mag is also right-side-up but facing the back of the copter.  I'm running the 3.3.4 beta, but I've had the same issue with 3.3.3.

Uncommanded Yaw 1.bin

33 6-5-2016 4-57-36 PM.bin

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  • Could you solve the problem?

    I had almost the same. My pixhawk decided to do a random hard yaw movement.

    • I finally figured it out, and (perhaps not surprisingly) it wasn't APMs fault, but a slightly loose motor mount that would rotate sideways in flight (only slightly though, so they still made enough lift not to crash the copter).  

      There was a clue in the log - the target yaw was lagging behind the actual yaw by 10 degrees.  APM makes sure that in most flight modes the target yaw is clamped to within 10 degrees of the actual yaw, so in my case the actual yaw was "pulling" the target yaw along with it as it spun.

      I am having an different problem now that I'm pretty sure is software-based, but I'm going to a separate post about that after studying the logs some more.

  • Plot your RCOU.Ch1-4 

    You will see something is very wrong, yes, as you lose yaw, motors 3,4 are very low, but the same happens around log line 91000 - without mych yawing.   (that should not be possible)

    Something is not performing correctly. While at hover, you should expect all 4 motors to be at about the same thrust setting, and unless yawing, 1,2 or 3,4 should not be far from each other.

    Screenshot from 2016-06-06 23-15-31.png

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