Weird loss of control testing AC3.1

Hi guys ! First post here :smiley:

So today I went for a maiden flight of the new version of my octocopter, loaded with AC 3.1 and all set to test the autotune on chanel7. But arriving at the field, I realize it was way too windy to test the autotune. So I started flying it in Stab mode with Simple mode activated. But since I was really curious to test the autotune, I fired it a couple of times : went to Alt Hold and fired the Chanel 7 trigger . The copter reacted as per the manual. Back to Stabilize and then I test Loiter. Worked great a few times until it completly go crazy, heading at full speed in one direction, so back to stabilize and I manage not to crash it. Then I take it for a flight to the other side of the field, and then it goes crazy again, just as if the simple mode was off. I managed to find the nose of the octocopter and bring it back close to me until it crashed becaue it was out of control.

Here is my setup :

Octocopter 1000mm 
Arducopter APM 2.5.2
GPS U-blox NEO + external Mag (RCtimer)
8 x 380kv Rctimer 4108 motors
8 x 40A SimonK OPTO ESC
8 x 14x4.5 Gemfan Propeller
2 x 5800 mAh 6s Lipo
Retractable Landing Gear

Logs attached.
Any ideas of what could happen ?

I forgot to mention that I did a Compassmot and the result was 10%.


I am still a novice at Log analysis but starting to put together a little Macro that can detect the common problems.

So far it finds three things in this log:

  1. Your GPS signal is not stable, you never receive more than 8 sats and at line 4000 and then again at line 9771 the HDop increases to 2+, not good from what I read. Research and provide clear โ€œhorizonโ€ view from above the props especially if CF one are fitted.

  2. Your Vcc voltage to the AMP is a little high, closer to 5v - Consider fitting the AMP Power Module
    [attachment=1]Vcc Voltage.jpg[/attachment]

  3. The fluctuation on the Vcc Voltage is very wide, this should be <0.15 volts