Pixhawk Flyaway

I had a disturbing experience yesterday. I was test flying my Hex and after a few successful hovers, a little PID tuning, and running through a few flight modes, I decided to let it stretch it's wings a little more.

On a fresh charge, I put it into Loiter, took it up a couple hundred feet, did a slow 360 and then slowly moved it forward.

Then, All of a sudden, the Hex sped up, headed toward the river, then banked to the right, spun around and put itself into a field about a quarter mile away.

Fortunately, no-one was hurt, and the Hex itself only suffered a couple broken arms and a prop - but needless to say, I'm quite concerned and want to get to the bottom of this before taking it out again.

I've uploaded the flight video to youtube at http://youtu.be/sc4UqOOiUUQ

I'm also attaching the flight log files.

I don't doubt it's related to something I did (or failed to do) and any insight would be greatly appreciated.

Cheers,

Adam

In case it helps - here the vehicle specs

-----------------------------------------------------

Tarot 680 (Carbon) Hex frame.

Sunnysky V3508 380KV motors

5S 4000mah Zippy Lipo

3DR Pixhawk, 3DR 915Mhz Telemetry & 3DR GPS unit

Futaba 14GS Radio

Mavlink connection to Droidplanner 2 on a Nexus 7

9.BIN

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    • My gut instinct would be to consider a 'failsafe' that decides when to ignore the accelerometers altogether. I understand that this could be problematic... how do you detect intense vibration? time averaging? min/max? And you can't just switch back into STAB, because of potential throttle differences. And how would you alert the pilot that they are in full control? Is GPS accurate / fast enough to attempt to bring the copter down by itself?

      And of course, while the developers feel the need to compensate for this risk, there is always the possibility that the simplest solution is better education about any automatic mode's dependence on acceleration and the importance of good vibration dampening.

  • Hello Adam, 

    I'm sorry for your copter,

    had exactly 2 times the same problem, have replaced all ESC. There were priced with inserted cable. Have 6 new soldered. My hexa is still flying healthy :)

    sorry for my bad english Greetings from sunny Germany

    ciao Klaus

    • That's my #1 suspect right now - see my response directly above for more details.

      Awaiting the arrival of 6 new ZTW spiders rated to 6S and 30A

  • In log alt and baro alt very strange, Alt -150! but baro alt +80.

    • 1, Z accel    (Mechanical?)

      2, Alt down to -150

      3, ThrOut   Max

      4, Descend full speed to hold -150 alt

      alt.JPG

      • i think this guy is right. as soon as your copter started moving (easy to tell by LAT because you were in loiter so long beforehand) your accelerometers are going nuts. Desired X & Y accel is +/-5 (centered at 0) and Z between -5 and -15 (centered at -9.8). 

        Your X hung out around -5, but your Y was drifting between -10 and 20, with your Z fluctuating between 0 and 60! (based on IMU) I would definitely say that your pixhawk came detached and was vibrating, leading to erratic behavior.

        public service announcement: always switch to stabilize when in doubt! stabilize doesnt care about acceleration, just orientation.

        Help me out here guys, I'm not familiar with the pixhawk. There is also IMU2 - in the 'high stress' region the readings differ significantly from IMU. is this due to the nature of vibration, or could this be indicative of something else?

        • I agree, it sounds like the flight controller came loose.  Those are not X and Y values that make any sense with it firmly attached.

          • I'll double check the actual connection, but I'm pretty sure the Flight Controller didn't come loose, Even after the crash it remains firmly in place where it was originally mounted (3M VHR tape).

            My #1 suspect right now is the ESC's I originally intended to use 3S & 4S batteries, but after being shipped 380KV motors rather than 580KV, I decided to run 5S rather than return the motors.

            I completely overlooked the fact that my ESC's (Afro Slims) though having plenty of headroom for Amperage, were only rated to 4S.

            I'm wondering if the patterns of failure shown in the logs would be inline with the type of failure that could be expected by driving an ESC over voltage.

            • i would expect a higher voltage to just burn up your esc electronics, not have any effect on the flight controller...

              i don't know what pixhawk internals look like - perhaps a screw is loose, and the flight board is rattling around inside a case? it just seems very improbable that an electrical problem would cause this obvious vibration....

              hmm, actually, you drop very suddenly to 18v as soon as the erratic behavior starts. i dont log my voltage, so i dont know if this kind of drop is normal. could it be caused by some kind of electrical problem, or is it just due to the high throttle requested during the flyaway?

              it does seem strange to drop to 3.6v / cell after only 3 minutes....

              3702866402?profile=original

              • That is a pretty significant drop in voltage. Would motors running at full power through an ESC not designed for it cause that big of a drop?

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