Can anybody help analysing the cause of this crash?

The copter started a test mission without any troubles and after reaching a waypoint, he started to yaw constantly but continued to follow the mission path.

After a couple of seconds the pilot switched out of AUTO mode into PosHold and then down to STAB, but the copter kept on spinning. The resulting oscillation of trying to get the copter stable and dealing with the ongoing spin resulted in a crash.

When I looked at the log-files, I can see the actual yaw following the desired yaw nicely. Until this very certain waypoint where the desired yaw goes up to 360, stays there for 3 seconds and then drops to 0 and stays there - all still during AUTO mode. When the desired yaw goes up to 360, the copter started its constant yaw and did not stop unitil crashed.

We are aware of the z-vibrations being not super nice, but I am pretty sure that this is not the cause of this behaviour. The copter holds it's altitude pretty nicely.

Frame type is a X8.

Any ides or suggestions?

Any help is greatly appreciated!

Regards

Marc

10.BIN

2016-03-09 17-34-25.tlog

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        • Dear Community, hello Cala,

          as i am the user of the system i could take a few photos.

          Please find them attached to this post.

          Greetings

          Alex3702810412?profile=original

          3702810504?profile=original

          3702810437?profile=original

          3702810477?profile=original

          • I have had similar result after motor mount twisted in flight. Don't forget the whole arm can twist too.  I've found single tube arms to be such a pita, I won't use them anymore. Without a locking hole/groove at both ends you can't be confident not to get twist but putting those in carbon significantly weakens the arm.

    • @Cala,

      thank you.

      As I notef before, to study AccZ we need to normalize AccZ as

      AccZ.normalized = - (AccZ + G) = -(AccZ + 9.8xx)

      G is all about weight of the drone on the ground

      Drone.weight = m x G

  • @marc

    could you attach IMU, GPS log charts,  track over Google Maps ?

    "

    Until this very certain waypoint where the desired yaw goes up to 360, stays there for 3 seconds and then drops to 0 and stays there - all still during AUTO mode. When the desired yaw goes up to 360, the copter started its constant yaw and did not stop unitil crashed"

    Desired yaw set at 360 from your Mission Planner ?

    DJI implemented mission preview to prevent a drone to fly mission impossible.

    What about all IMU1, IMU2, Kalman filter, compass, GPS heading data ?

    From IMU.Accel data you can easily track performance of all of your motors.

    Do you know phys-math-IT model adopted to control yaw in X8 ( yaw vs. pitch and roll algorithm) ?

    BTW.

    There is one flight mode keeping your drone to spin around, pointing camera at target.

    Open Technology Park

    Open Fabrication Lab

    Peer To Drone Crash Investigators

    manta103g@gmail.com

    • Darius,

      The .tlog and the Pixhawk-log is all I have.

      As far as I can see from the logs, the direction north (360°) was intentional as the mission had to continue in this way. But the drop back to 0° DURING auto mode is suspicious.

      I know the basics of the underlying flight models that keep those things up in the air, regardless of its frame configuration or type of aircraft.

  • From the logs it looks like it was trying to stop the yaw but was unable.  I would do another test flight in position hold or Altitude hold mode and yaw it in one direction first and then the other directions and provide the log here.

    You should see in the log a similar output as your crash log.

    A single motor failure should show up as the bad motor going to max and the opposite motor going to minimum.

    • Michael, will do that. As I did not fly the copter nor do I have access to it, it will take a while before I get the desired data.

  • From the logs I can see that at the point where the Yaw went to max and then min that the copter started turning counter clockwise but the even motors went to max and the odd motors went to min to try and get the copter to yaw clockwise.

    This would indicate some kind of motor failure such as maybe one came loose and turned or a prop came loose.  When a prop comes loose you usually see that motor go to max but it looks like all the motors responded together.

     

    • Michael, thank you for taking a look!

      It's an X8 and even with one motor completly shut down, it won't spin.

      After a whole day of bench-testing, no mechanical or electrical issue could be found.

      So if there was no failue in the frame causing this VERY constant yaw, who commanded it? Why did the autopilot decide to set the desired yaw to 360° and than to 0° during the mission?

      And why didn't the copter stop yawing after switching out of auto mode?

      • Have you tested your hypothesis of "It's an X8 and even with one motor completly shut down, it won't spin."

        My experience tells me the opposite.  When test flying a few different X8s I've built with only 7 props, they spin like a top.

        "And why didn't the copter stop yawing after switching out of auto mode?"

        I would bet on either a) motor failure as Michael says or b) a motor mount came loose or twisted on the boom during flight.

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