Very dangerous quadrotor fly away!

I switched my pixhawk into loiter mode and it started to gain altitude so I immediately throttled down but it refused to slow or cut the motors. The thing continued to gain altitude until it reached 100m. Roll and pitch were still controllable so I held it in position over the park I was in until it plummeted out of the sky. I throttled up again before it hit the floor to try and reduce the impact. Does anybody know what may have happened?

I would like to attach the dataflash log but the txt file is greater than 2MB. Is there a way around this?

@samfrang,
Either zip the file or provide a link to it on Google Drive.
Regards,
TCIII GM

Thanks @TCIII, here is a link to the dataflash log:

drive.google.com/file/d/0B3CuPP … sp=sharing

Your Z axis vibrations look terrible.

Are your props balanced? how is the FC mounted?

@MarkM Perhaps that was the problem here. This is a small quad that I am using for tests after a much more dangerous crash that happened on my bigger one (it’s about 1m^2 and has 16" props).

On the bigger one there was two problems – it had been configured on mission planner as an X but wired up as an H (the difference being the prop rotation) so that yaw was inverted. It was started in loiter mode and immediately started spinning so I throttled down but this had no effect (second problem). It then started to rapidly gain altitude and was only stopped when it began to circle and hit a wall.

Is it possible that it was positive feedback from – an error in heading+ trying to spin the wrong way to correct it – that meant that it wouldn’t power down?

That was my first theory but now that I have moved the pixhawk onto another (correctly configured quad) and had it refuse to throttle down again, I am beginning to think that there must be something wrong with the pixhawk.

Here is the dataflash log from the first crash:

drive.google.com/file/d/0B3CuPP … sp=sharing

@Mark M

Just looked at the z axis vibratrions - at the low altitude (i.e. when the problem started) they don’t look that bad to me. Aren’t they roughly within the -15 to - 5 range recommended here: copter.ardupilot.com/wp-content/ … _Vibes.png