Sudden motor failure in small hexacopter

I’m setting up a small hexacopter (300mm frame), finally to be used to make 360 images. No racing or fast flying required but stability is most important. During the last couple of test flights the hexacopter, after a few minutes of stable flight, suddenly flips over and crashes (fortunately always in the grass so no major damage). After the crash one of the ESC’s (3) gives a continuous dual tone singal. When I look into the log file, the problem starts around T= There suddenly RCOU drops from around 1300 to 1070, or so. I cannot figure out what is the cause of the failure and I’m not sufficiently experienced to read the log files.
The specs of my drone are:
Frame: 250 Spedix hexa
FC: Omnibus F4 Pro with ardupilot 4.1
ESC’s: 12A with SimonK (have not found out how to flash them with BLHeli…)
Motors: 2205 2300KV
Props: 5x4 (6blade)
Battery: 4S, 3.3Ah, max amp drawn from the battery generally around 10A during hovering

Here’s the log file:

Hope someone can help me analyze the log file and point me to the cause of the problem.

Motor output 3 is commanded high because you have a lack of thrust on Motor 4 (opposite arm from 3). Classic case.

You cannot flash old SimonK based ESC’s with BLHeli. Suggest you replace them with BLHeli_32 units.

Also, you have MOT_SPIN_MIN lower than MOT_SPIN_ARM. That’s not right.

And, if you have a compass connected it’s not being recognized.

Hi Dave, thanks for your quick reply! The motor which seems to fail is right-rear, and indeed that’s M4 in the hexa-configuration (sorry I confused the M-numbering with the numbering which is used for testing the motors). Is it possible to find an indication in the logs what the cause is of the failure of M4? Is it likely to be a configuration error or more likely to be a hardware problem, for instance the ESC?

Currently there is no compass, so that’s correct.

Log data doesn’t really show a cause of thrust loss. If you have ESC telemetry you may be able to make some guesses by looking at Motor RPM, Command output and voltage/current. I would say it’s a hardware problem. Prop,ESC or Motor failure or perhaps a solder joint or wiring.

I saw a mode change failure message, that’s why I looked for the compass DeviceID in the Parameter file. One more thing is you have the Dynamic Notch Filter enabled for throttle reference but 0 for the reference value.

Unfortunately with these ESC’s there’s no telemetry. I’ll go through all other hardware, but I guess the ESC of M4 is the most likely target. I’ll have it replaced, as I do have some spare ones. Otherwise I will have to go for ESC’s with more recent firmware…
Thanks for your help!