13kg VTOL Motor 2 fail mid flight

New ESC, new motor, new wiring and calibrated completely. Quadplane hovers for a few seconds then motor 2 fails. Running latest firmware. Please assist.

Cool failure report but how can we assist on it?

Well if I can load the bin file I would. It says too big.

use a cloud server service like google drive

2025-01-29 14-20-54.bin

Has this been correctly configured using ArduPilot methodic configurator?

On a big vehicle like this one it is irresponsible to not use it.

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For reference on this setup: (and to keep it straight in my own head)

SERVO5_FUNCTION  33.000000 # Motor1
SERVO6_FUNCTION  34.000000 # Motor2
SERVO10_FUNCTION 35.000000 # Motor3
SERVO8_FUNCTION  36.000000 # Motor4

Was this VTOL actually flying or where the props installed? Because there is a torque split here that should have that plane spinning in circles.

Motor 2 (RCOU.C6) is being commanded to full, but the total current drops with Motor 1 (RCOU.C5). This is typically a sign of some kind of failure in that arm for Motor2. Motor, ESC, wiring, etc. It’s not flight controller or ardupilot issue. The controller is trying to manage the torque so it backs off Motor 1 and ramps up motor 2, problem is that it doesn’t know that motor 2 isn’t working.

I suggest investigating that arm and figure out the cause of the failure. I’d also try to find out why there is such a torque split between motors 1&2 vs 3&4. That’s a big problem.

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Video of the flight:
WhatsApp Video 2025-01-29 at 13.10.03_e24d2a3e.mp4

@Wheelventure
It’s good that you had only reached a height of 20 cm, so the damage is probably minor.

@Allister has already found out the cause of the crash and described it in detail. Your video is just confirmation, because it was difficult to tell from the log file whether you had already taken off.

Unfortunately, the ESCs do not have telemetry (or you did not activate it), otherwise it would have been possible to see whether the ESC of motor 2 (rear left) was thermally overloaded and switched off. This is of course speculative, but motor 2 was already running at saturation. A cable break or loose plug could of course also have caused this. In any case, it has nothing to do with Arduplane Software.

What is more exciting is why the CCW motors (1+2) are partly in saturation and the CW motors (3+4) are partly completely down to idle speed in order to compensate for torque around the vertical axis. Have you inadvertently mounted different CW and CCW propellers? or are the motors mounted tilted differently to one side?

Quad-X configuration:

Rolf

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Thank you @Rolf. The props are as per diagram above. Motors are all tilted inwards at 5deg. We changed the connectors on motor 2 and will test again.

No change.

You need to fix that torque split. I don’t know how you set the 5 deg tilt but you need to check that it is perfect, the props, everything. It’s very possible that the torque split is contributing to the motor shutdown. I mean that because motors 1&2 are working at maximum (vs 3&4 at minimum) that the ESC is over heating or there is some other protection kicking in. Fixing the torque split may solve the problem for motor 2.

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Observing the plane visually, I think there is a very clear CG issue which causes the different power requirement between front and rear motors:

From what I see the arms have about the same length from leading edge and trailing edge. Normally, a plane has CG at 25…30 % from leading edge. If this plane has its CG set up correctly for the plane mode, then the whole setup will require about 50 % more power for the front arms motors than rear motors for hover.

However, the PWM difference (1200uS versus 1800 uS) would most probably cause a much bigger power difference.

But the motor numbering contradicts that, i.e. motor 2 should conumse much less power than the front motors.

What I would do is to temporarily load the tail with weight, so that the CG would coincide with geometric center of motor frame and test the hovering. If this solved the front/rear power issue, than you have to cut off the rear arms by about 30 %, so that the rear prop disk would be touching the TE.

If you have a lot of extra power (like you can hover at 30 % of max power), one can get away with incorrect CG hover, but if your setup is close to minimum, your setup is not flyablle (aka hoverable).

To check out if the motor/ESC are OK, I do the following.

Set all 3 other good motor servo output to nothing and or remove props.
Set the motor servo which is suspect to Throttle (RCIN3) direct, and leave the prop on.

Then, tie down the plane and start pumping/playing with the throttle trying to recreate the failure. Danger! There is no arming involved, the throttle controls the motor immediately on power on.

From the looks of it, it was like a complete shutdown, this could be due:

  • Thermal shutdown (very unlikely, but looked very similar)
  • Intermittent broken wire
  • Syncronization issues (to test for this, you have to try and move throttle from zero to full very very quickly).

The power difference is not front/rear. It is CCW (motors 1&2) and CW (Motors 3&4). Check out @Rolf’s image earlier.

Thank you for aal the feedback. Motor order is correct. Props are correct. CG is perfect on 25% from leading edge. We tested a few times.
We decided to change to multirotor and test again. This time motor 1 cut out.
I must add that we are using T-motor Flame 80A ESC’s with V505 Kv260 motors and 17" props.
Multirotor test bin file:
2025-01-31 10-18-56.bin

CG 25 % is perfect for Plane mode, but ABSOLUTELY NOT PERFECT FOR HOVER, because your arms are clearly centered around the wing center, i,e. you have to have CG at 50 % to be perfect for hover. You probably can get away with it as is and your problems are not due to this, however a good design would call for cutting the rear arms by about 20…40 % so as to make coincide perfect CG for Plane and perfect CG for Hover.

PS: yea, on first reading of graphs I did not realize that the uneven power was diagonal, not front-rear.

I would check the temperature shutdown parameter in ESC. Usually it is 140C, or no limit, but there is also an option for 80C, if you somehow changed that to the minimum value, it could well be that you have a thermal shutdown. From the looks of it in the video, it is very similar.

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I’m guessing you didn’t get as far into the air this time.

All the motors are being commanded equally, in that motor 1 (or 2 from before) is not being singled out in the commands from the controller. So if one of the motors is cutting out there must be some external reason. In this case it doesn’t look like load since other motors were working harder. Voltages were in range for 12S. I can’t speak to heat or anything like that, but it would be worth looking into if you had done other tests or the plane was in the sun, or whatever. And of course power distribution, is there some kind of failure there.

Edit: I just noticed on the T-motor website that those ESCs will shut down if there is a signal loss for more than 0.25 seconds. They are supposed to start up again, but it got me thinking that it could also be an issue with the signal leads or wiring there.

In my builds, I normally do this on the drawing board to determine the quadmotor boom lengths and position. To determine the actual adjustments you need to make to have both your CGs match, you can get a thread/string to Motor 1 shaft to 2 shaft, then from 3 shaft to 4 shaft. The difference of the thread/string intersection point to the 25% CG point is the distance you need to adjust for your quadmotors; e.g. if the intersection is 50mm behind the FW 25% point, that will the distance you’ll need to move the motors forward.

Good luck.

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It seems this horse may have been beat to death already, but just in case here are some of the things that I check in similar instances as I have had brand new Motors fresh out of the bag come with a melted winding at least two times that I can recall:

  1. Smell all four motors. If you have a burnt winding inside of one of those motors, you will smell an acrid odor. If that is the case, toss the motor and install a new one.

  2. For all wires going into an out of the Esc check for wire discoloration, it’ll be a darker hue than the rest of the colors. Sometimes that discoloration can be from a solder job that was just too hot and other times the wire will be completely burnt right down to the copper. C

  3. For all wires connecting directly to the auto pilot servo rail make sure that nothing has jiggled loose.

  4. For every ground, signal and positive wire connecting to the auto pilot servo rail pull on each individual wire. Sometimes you can have a bad crimp that will cause an intermittent signal loss. You have to be very thorough on this check as the looseness can easily be overlooked. I suggest tweezers.

  5. Visually inspect the capacitors on each of your Esc‘s, when an ESC fails it is usually the capacitors.

  6. Check that all of your props are tightly screwed down. I’m not kidding, check them. I have lost birds because of that.

  7. Spin up your motors and check that the rotation commanded by the auto pilot is correct and more importantly check to make sure that your prop is not installed backwards. A backwards installed prop will generate some thrust, but nowhere near full thrust.

  8. Do not be afraid to sacrifice a chicken. I find that sometimes this makes my bird fly quite well.

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A simple handheld thermal camera is a great tool for investigating thermal issues. They are relatively cheap compared to a large VTOL drone. Strap the aircraft down and run the motors at expected load, then inspect for heat issues.

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