Why my quadcopter crash

ArduCopter Copter 3.6
1

May somebody from this DataFlash log say why my copter crashed.

43 6.1.1980. 9-19-08.bin (810.2 KB)

2

Plot RCOU for C1 thru C4. Look at the plot for C4 (motor #4),

3

Please, what you think,what’s happened with motor #4

4

Two possibilities. Either the ESC is bad, or the motor is bad.

5

I checked motor and ESC, it’s O.K.
Did you see that motor #4 go to minimum when I changed mode
from Stabilize to Loiter Super Simple.

6

DUH. There is definitely something wrong with that motor/ESC combination.