Need help diagnosing a mid-air prop stop

Quick self intro: I've been into multirotors for only a little over a year.  In that time, I went from an RTF Phantom to building my own tri, hex, quad and now working on an X8.  I mostly run APM 2.5/2.5.2 on the home-built craft.  I usually fly 3.0.1, but have been playing with 3.1.

On my latest quad build, I was on a tuning flight using APM 2.5.2 with Arducopter 3.1rc8.  After switching from stablize, to alt hold, to auto-tune, to loiter, to circle, back to loiter, I had a prop just stop spinning with the craft about 60 feet off the ground.  I suspect it was the AFRO 20A ESC losing sync, but I have no hard data on that.  The other three props were spinning fine still so I don't believe the problem to be power-related.

I unfortunately did not have the power module installed yet, so I don't have logs of the amps and volts.  I did have IMU logging enabled though, as I was tuning the quad.  Is there anything in the logs that can help me determine the cause of the failure or point to any clues?

I've uploaded my log from that flight.  If anyone could give me pointers, I'd appreciate it.

Thanks!

2013-12-11 22-38 1.log

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  • Quick update:

    I've just reflashed the Afro 20A ESCs with a more recent version of SimonK firmware and it seems to behave MUCH better.  I can't get the ESCs and motors to lose sync, even with fast full and reverse throttle/roll/pitch.  At one point, I had two ESCs with the new firmware and two with the old.  The original/old firmware ESCs constantly lost sync while the updated ones never missed a beat.

    I'll only know if the problem is fixed completely with more air time.

    Thanks all for the advice!

  • I had a couple of APM flips before I switched to powering the board with clean power. If you look at the archives here you'll notice that brownouts are the most common cause of flips.

    Its also possible that IMU logging was the cause. The extra processor overload could have caused it, AC3.01 makes the processor work a lot harder than with earlier firmwares, due to the presence of a larger numbers of features and parameters. In my case, once I had finished with the initial tests requiring IMU logging (such as vibration levels), I disabled it. I also disabled FENCE and various other failsafes prior to doing my AC3.01 testing, and my quad flew perfectly. I'll probably only add those bells and whistles back when I have a PixHawk.

  • I haven't done much with logs before, but just looking at the ThrOut (CTUN row), towards the end are some really weird throttle values (looks like they're maxing out).

    However, if you look at the ThrOut trend, it does seem like over time the APM is increasing the throttle more and more to keep it at a steady altitude, which could mean a flat battery. It starts out at about 600 or so, and by the time it looks like it crashed, the throttle was more around the 700 mark.

    Did you measure the battery voltage after the crash? Even if you got a reading that seemed normal, the battery voltage can drop sometimes up to a volt under heavy load and depending on the age/quality of the battery. If you saw anything less than around 11V after the crash, I'd be worried about the ESC simply cutting off.

    You'll find even with all the exact same ESCs, they won't all cut at the same time.

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