Help diagnosing in-flight seizure

I have a few solid hours flying my Vario in Auto missions and have not had any real issues.  Today however, once RTL was engaged at the end of a test mission the helicopter went into what I am calling a seizure!  The heli oscillated in pitch and roll very rapidly, it was frightening.  I switched to Loiter and nothing changed, then switched to Stabilize and the oscillation stopped.  I brought the heli down for a landing but before I landed I switched back to Loiter to see how it would behave, and it was fine.  After this I was able to do two more successful Auto flights using the exact same mission.  I looked at the log and I can see the "seizure" in the graphs but I do not see anything that would have caused it.  

If anyone can review the log and lead me into a better understanding of what happened, I would greatly appreciate it!

Chris  

16.BIN

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Replies

  • Hi Chris, just a question, what is your headspeed? I had a look at your log, and it seems your PIDs are very well working.

    I explain better my idea, if for example the M/R RPM are going up too fast, and you already are at the spot point with the P-I values (for the nominal RPM), it could happen to have some "bad" oscillations (Robert correct me if i'm wrong). Even if a governor is fit, you have transition phases in which a  bit of lag could be experienced (especially in high inertia rotors, like ours...). If you see the attached picture, the vibrations just happens during the final descent step. That could agree with a temporary "unloading" of M/R during descent and a slight RPM overspeed. For example on my Benzin, I tuned the PID's for a 1250 RPM headspeed (maximum recommended by Vario as far as I recall...) but operational headspeed is about 1150 RPM. That because I experienced a very "bad" behavior like yours during a simulated flare (gov was still on...so engine running) , head overspeeded a bit too much. To me it sounds pretty normal you had to force it into stabilize to stop the shaking, because in that way collective went up a bit slowing down the head almost immediately...Hope it helps.

    Regards,

    ferruccio3702067481?profile=original 

  • Hi, I had a look. I can't see the cause.  There's some high vibrations at the time of this event, but there's a chicken/egg thing there that we can't resolve.  I do see that the servos were moving in the same frequency as the oscillation, but again, chicken/egg.  

    I do notice that, while you said you engaged RTL, that does now who in the logs.  Are you sure?  The oscillation starts before you engage Loiter, then Stab, then Loiter again. I don't see a Ch5 input change before the first change to Loiter.  

    I wonder if your Rate PIDs are borderline, and something, some external disturbance, just lit it up?

    On a side note, I notice that your COLYAW is -5.  Does the Vario rotor rotate counter-clockwise?

    • Thanks for the reply. 

      When I mentioned engaging RTL, that was the last waypoint in the mission, no Ch5 switching.  What you said about the Rate PIDs I thought as well, although the graphs all line up pretty well.

      About the COLYAW being -5, yes the Vario rotor spins counter-clockwise.    

  • I had something similar to this event happen again yesterday, this time just after take off.  The log file shows a drop in GPS sats from 12 to 8 for a second at the time of the event, other than that I dont see any issues.  

    Anyone have any thoughts on this? 

This reply was deleted.

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