Motor failure during flight

ArduCopter Copter 4.0
1

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:

image
image3233×789 220 KB

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:

2

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.

3

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

4

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.

5

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.

6

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.

7

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.