Unexpected (strange) crash

Hi all,
yesterday I have a strange crash. Quad was hovering (in stabilize mode) and suddenly began to oscillate and droped down. Battery was charged.
Before it flew very well (in stabilize and alt hold). Why does it happened?

P.S. After all, I saw what battery was little bit swollen (one cell).
PP.S Sorry for my bad english :)

Quad info:
Board - APM1 (with 2.6 soft)
Frame - custom
Motors - DT750
Props - 12x4.5
ESC - SS 25A
Batt - 5000mAh 3S

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  • mine has been doing this a little, although i only flew for the first time yesterday ,

    i have read that over aggressive PID can cause oscillation, and in my case it goes crazy when coming down fast, but if i give a little throttle it levels and i can bring it down slowly,

  • Checking the battery unloaded isn't going to tell you a whole lot.  The fact that you've got a swollen cell is very, very suspicious.  It's entirely likely that cell's output voltage drops badly when you start pulling some current out of it.

  • Possible. But after crach I cheked all cell voltage. All cells was the same - 3.79V

    I will try to attach log.

  • Developer

    Sounds exactly like a low voltage issue. double check those batts.

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