Diagnosing ESC fire on m0138

Martin Lukac

Hello!

We have a m0138 we received a couple weeks ago. The setup we are working to test out:

6S battery (more details below)
2812, 1100kv motor
8046 3-blade props

During a calibration it caught fire. We are looking for help to diagnose whether this is a bad combo, a soldering/short issue, or a bad parameter, or something else we can't think of. My detailed questions are at the end and we would appreciate anyone with experience taking a look!

Note - all tests run on #2 esc/motor.

We first tested the calibration with a 6S 2200mAhr 50C battery. I did a firmware update. Then I started with this file and modified the KV (and the tones), and loaded the file onto the ESC.

I did the spin test on, and then ran the calibration and it was fine. I have plotly installed but it complained (maybe something wrong with my env) so it didn't generate the calibration html file. I did capture the console output and included for calculating the min and max rpm. See the file labeled goodtest-notes here. Everything looked fine, temps were good, motor was just little warm, current went close to 40.

I put the result of the calibration and min/max rpm into the xml file here and loaded it onto the ESC.

A few hours later a bigger battery was charged. I connected to the same setup except and did not change any parameters except I replaced the battery with a 6S 2P 9Ahr battery (also known as a P45B). The battery is 10C max continuous.

I had the same plotly issue, so see the notes_fire.txt here. You can see that it got to POW: 73, then it stalled/desynced, tried to ramp up the power again, then dropped the power, and the temp kept going up and it aborted. I was behind a door and it sounded like it finished so I looked at it was on fire. See image below.

How should we debug this? We have another couple m0138's but we are hesitant to try.

Can you review the outputs? Does our motor, prop, battery combo make sense here (we are going for long duration).
Could this have been a short? something about our wiring?
Anything weird in our parameters? Did we start with a good file?
I saw some threads about a capacitor, would adding one help here?
What can we do to ensure there are no future issues?

Thank you!

Here is a picture of the result -- it was mounted in a frame properly isolated but we removed it:

Alex Kushleyev

Hi @Martin-Lukac ,

I am really sorry this happened to you! the damage to the ESC is quite spectacular.

I will need to think about this a bit more, but my initial guess of what happened is as follows:

as you mentioned, during the failed calibration attempt, there was a de-sync event, which may suggest the demagnetization time of the motor coils is higher than usual (this is one possibility). A fresh (and larger capacity) battery could have resulted in higher voltage + lower output impedance, causing higher current spikes in the motor (longer demag time). Usually this does not happen with motors of this kV (but much lower like 700 or lower), however it depends on the particular motor.
after the de-sync (which it looks like the ESC detected and attempted to restart), the start-up potentially failed because the motor was spinning very fast and it could have gotten into a weird state, applying 80% power to a motor that was not spinning properly. However, in this case i would expect the motor to burn up first before the ESC. Did the motor burn out as well?
- to resolve the de-sync problem, we typically increase the esc commutation and sense advance (I can go into detail later), but this is documented here: https://gitlab.com/voxl-public/voxl-sdk/utilities/voxl-esc/-/blob/master/voxl-esc-tools/doc/low_kv_motor_tuning.md
the unfortunate part is that during the motor calibration, the motor is controlled with % power, not RPM commands, and there are fewer safety checks. If this happened in RPM mode, the ESC would have most likely prevented applying such a high power while motor was spinning very slowly.

Considering the outcome of your testing, my recommendation would be for us to test your motor / prop configuration and see if there is a repeatable issue. Are you able to share the exact motor and propeller part number and where to purchase it, if possible?

Thank you

Alex