Motor failure during flight

I have a hexarotor that has been running fairly well for about a year. However, during a recent test, there was failure in one of the motors during an Auto mission. We did a couple of hover tests in Position Hold which went fine, but the minute I switched into Auto there was failure in one of the motors. Here are the drone’s specs:

Frame: Tarot T960
ESCs: Hobbywing X-Rotor ESC - 40amp (OPTO)
Props: 18 inch
Battery: Turnigy Graphene 6S 12000 mAh
FC: Pixhawk 2.4.8
Firmware: Ardupilot 4.0.5
Max all up weight: 12 kgs
Current weight: ~7.5 kgs

I’ve had several successful flights in the past without issue so I am not sure what happened here. Tried powering it back on after it crash landed and all motors were spinning up fine in throttle tests so it seems unlikely there was a loose connection somewhere. Anyway, here’s a plot of the RCOUT vs battery:

Some additional notes:

  1. During the malfunction, GCS showed:

Potential thrust loss (6)

even though RCOUT.C5 seems to bottom out in the graph.
2. In addition, GCS also showed:

Prearm Board 4.1V out of range 4.3-5.8V

This might be because I am using a Drotek 200A power module in lieu of a 3DR 90A power module. Again, this error has shown in the past but I’ve had several successful flights anyway. Both the .bin and .tlog files are attached below:

No, loss of thrust on RCout6. When it’s commanded to max it’s due to lack of thrust. “bottoming out” is the attempt at stabilization on the opposite arm.

That makes sense. But why did that happen? Any thoughts welcome.

Not sure if it’s related but the FC Vcc is way below Brown out voltage dropping to 3.78V at one point. And why run V4.0.5? Update to latest Stable.

Yeah, I was concerned about that too. Guess the:

Prearm Board 4.1V out of range 4.3-5.8V

warning should not be ignored.

Yea, check the power module output. But I had one of those 2.4.8’s and I didn’t trust what was always reported for Vcc. I don’t use those anymore.

I agree. I have a Pixhawk 3 Pro which is compatible with the Drotek power module. There are no Vcc issues on that board with this power module even in Auto missions. I am just going to switch over to that. The reason I was not using that was because some time ago there were some bootloader issues with Ardupilot. This is why I was stuck on 4.0.5. Those issues are fixed now so I’ll be able to use the latest stable.