Good afternoon.

I successfully built my first heavy lift using U8 motors, Pixhawk, T70A ESC etc and launched it for two flights on Friday. All working pretty well, although it was very twitchy and oscillated quite a bit after a large movement.

No problem, I am assuming that I need to get some better PID values in or try Auto tune.

This morning I made sure all flight modes are working smoothly - stabilise, alt hold and loiter.

Long story short, it started to oscillate like crazy. I kind of got it under control (still in alt hold) and went crazy again. Switched to stailise and it was ok, coming down slowly, then went crazy oscillation again (mostly left/right), and finally dropped down and into a tree.

The tree was a blessing - completely saved the copter. Almost no damage  !

My initial thoughts were around PID and oscillation. It was a little gusty up there, and the copter did oscillate a bit during small inputs when I first launched.

However, looking at the logs, my second thought is now the radio. The radio signals are all over the place, and that was not my twitchy fingers, I was calm. OK so we could assume radio lost. But then I plotted channel 7 and 8 - I only have an 6 channel receiver (Spektrum) going into a 3DR PPM encoder - and yet even channel 7 and 8 seem to be crazy in the logs - although since they are actually floating inputs, maybe that is correct, so it could be just that the receiver went bad.

I am trying to determine the cause of the oscillation - the crash itself was only part of that.

One other change I want to make is to have the props always spinning, I think there is a setting which allows minimum input on arm - that way I can make sure they never get too slow into the danger zone for sync issues.

Looking again - I am definitely not certain that it is radio issue.

Could someone please have a look at my logs. Thanks.

2014-10-4_2-31_58.log

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  • More testing today. Checked the radio in range mode at 50m - still working fine. So I don't think it was the radio. Also reducing the RC Feel to make sure I am not giving it undue feedback. And flying on a calm day. Lots and lots of reading on correct PID values - manual tuning rather than Auto tune.

  • FYI - Channel 6 & 8 are a red herring - they are floating inputs and not used, so I think I can ignore those (unless they are doing something, maybe I should be grounding those).

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