I installed 2.6 this evening and took it out to do a bit of close-in, low altitude test flying to see if my tuning was still good, just before it got dark here. Before today, I had been flying 2.5.5 without issues (besides a yet-to-tune loiter). This first flight with 2.6 went fine too, until...

...a few minutes into the flight, while I was in Stabilize mode I think, the quad suddenly started accelerating vertically, climbing away. I zeroed the throttle, and jumped into Land mode, but got no reaction. I was flying next to a tree, and the quad lodged itself high in the tree crown, preventing a total fly-away. It hung there, props spinning at high throttle like a weedwhacker, for a very-long feeling time (maybe a minute), until it came loose, tumbled down and smacked in the ground.

I flipped through my modes and wiggled the controls while the quad was in the tree, getting apparently no reaction, but I did not have the presence of mind to try to disarm it. (Note to self: remember to disarm.)

A couple of broken legs, a set of chipped props, a few popped screws and a broken cheap camera mount seem to be the only hardware crash damage - not a problem, thanks to the 3DR frame engineering. As a positive side effect, it was good to experience that my heart does not actually stop in this type of situation :-)

In my flights over the last few weeks since building the quad, I have not experienced any unpredictable behavior, scares or radio problems. The props were balanced and the battery had plenty of power.

Setup:

3dr-b frame, 880kv motors, 11*4.7 APCs, APM2, 3dr radio, sonar, optical flow (not tested yet), 4s1p LiFe 4200mAh battery, DX8 TX, AR6210 RX with satellite, DSMX.

I am attaching the log. It gets interesting just after 90% / 600s.

Needless to say, correlation is not causation. This might not even be a 2.6 problem or (like many quad issues) a software problem at all.

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Knut, thanks for posting the logs. Can you repost this in the 2.6 thread? We need to keep all the 2.6 feedback together. 

can you post your Flash log as well?
Jason

Jason, downloading the flash log to the planner now.

Chris, good point. I will repost once I have the flash log.

Graphing the log myself, I see that the rc inputs go flat a couple of seconds before the unexpected climb starts. I suppose that could be an RC connection failure, followed by what looks like a behavior similar to the rtl-failsafe for Auto mode. I wasn't in auto mode, though, and I don't have that failsafe mode enabled.

While the quad was in the tree, I power-cycled the TX, and that does not show in the RC inputs, also indicating that the RC connection may have been lost. I'll have to compare these frozen rc input values to my RX failsafe settings.

Closing this thread, did repost in the 2.6 thread.

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