APM 2.6 Crash log analysis

Hi all

I have no idea how does the multicopter crash.
When executing RTL, the multicopter start to tilt in a dangerous angle and then flip&crash
I had tested these modes: manual/althold/loiter/auto, and RTL function.
It works fine more than 5 flights. And I think it is stable.
But…

I’ve posted the detail to the following link
http://diydrones.com/forum/topics/apm-2-6-crash-log-analysis
Any help will be very appreciated !!
thanks

[attachment=0]20150103_Mechanical_Failures.jpg[/attachment]

This graph is derived from Mission Planner “Log Browser”. Maybe there is something wrong with the motors.

Besides, I found that the similar case by the following link
copter.ardupilot.com/wiki/common … sing-logs/
It says that the actual curve and the desired curve mismatch is caused by mechanical failures.

thanks all the people who like multicopters
BR

david_ls