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!
I made additional tests and I realized that when in AltHold, Loiter or AUTO there is a significant problem on yaw. In fact when the copter is in one of these modes it stays stable, but If I Yaw even very gentle with the stick, it drops very fast altitude or climbs fast depending on the direction of rotation (CCW looses altitude, CW gains altitude but I am no really sure about it). I thought this problem was solved from ArduCopter 2.7.3 version. The configuration for YAW RATE is :
I have attached the parameters list and also the log file. In Stabilize mode I made twice a 360 degrees turn CCW and the result was a 2 meters shift on the left. In Alt_hold and Loiter there's the quick altitude loss when yawing.
Thanks for your help