I had a strange crash with my foam quad in auto mode. The quad frame is the following:
It's a pretty big frame and very light. It has always performed very well in all modes with default APM parameters but it was very sensitive to the wind so I decided to perform auto tuning on it. After this procedure it looks to have a quicker response to commands in all modes, less overshoots and solid rock against light wind.
I had APM 3.1.2 FW version and made a very simple AUTO mission with 3 waypoints and heading on third waypoint the copter flipped but I was able to recover it switching to stabilize mode.
I downgraded to 3.0.1 FW version and made the very same auto mission. Same position same "flip", this time I was not able to recover it and had minor damages. It must be noted that after 2nd waypoint has been reached, in order to reach the 3rd waypoint, the copter had to make a 180 degree yaw. as in the previous test with FW 3.1.2
From log file, Roll and Pitch seems to follow RollIn and PitchIn well, but suddenly they did not follow the input anymore over oscillating and leading to crash.
I suspect that new value of PID moved the copter to some "instability region" for some frequencies of disturbs such as wind blows or yaw maneuver oscillation, but I might be definitely wrong so I do appreciate help!