Drone flipped after autotune

I just autotuned my drone, and then I flew it again to check its performance. Thats when my drone flipped and crashed. After the crash, smoke was coming out of one of the motor. On later examination, it was found that one of the ESC got shorted. This may have happened due to the impact from the crash. Kindly review my log file and enlighten me with the reason of the crash!
102 01-01-1980 05-30-00 AM.bin.log (877.8 KB)

I’ve changed the category of this post from “Blog” to “Copter 3.6” so that it appears in the support forums instead of on the front page of ardupilot.org.

I reviewed your log and it is obvious that your # 1 motor/esc failed. I had nothing to do with the auto tune. In fact the copter was very well tuned, no oscillation, and desired roll and pitch perfectly matched the actual roll and pitch. near the end of the log they suddenly diverge and the output to #1 goes to maximum while #2 goes to minimum as the copter is trying not to flip over. I would not use that esc or motor again even if they seem to work.
The motor may have smoked from a short in the esc and may still run afterwords, but the insulation would be damaged.
Bottom line is the failure happened in flight and not the result of impact. I did not see the impact on the accels, looks like the battery disconnected on impact as the log file just ends.