Root cause analysis - board failure

Hi there!

I got my simpleFOC board running nicely open loop on a large gimbal style outrunner, and thought I would use it with a smaller Nanotec motor I was using in an actuator application to try hall only positioning.

The board immediately let out the magic smoke running the halls positioning test code.

This motor has 0.6Ohm resistance, and 0.3mH inductance. Is this an obvious failure mode because I left voltages at their default and fried the driver? :man_facepalming:


Hey @AlexR-D,

This is likely what happened. The Shield is designed to work with motors that have a high phase resistance (usually gimbal motors). It is possible to use it with motors that have a very low resistance, like yours, but you need to limit the voltage in code to avoid drawing too much current and letting the magic smoke out. What were you using to power the shield? Were did you see the smoke?

I wonder what got fried? It could have been pcb copper or the l6234d. I think the latter is about £4. Fixable?

I had a 24V variable supply powering it. Looked like the 6234 was smoking, but after letting it cool it’s clear the linear regulator is also fried (makes that beautiful sizzling sound on power up). I’ll grab some spares from digikey and see if I can get it running with those replaced!

And I will be a little more careful compiling demo code :slight_smile:

Thanks for the feedback!

Is your power supply current limited?

It is, but… it was set to 10A.

Next time coffee first :slight_smile:


With low resistance motors paired with weak drivers you might as well also drop psu to 9v. There are some benefits to smoothness particularly on 8bit pwm mcus.

Also remember that the current on motor can be 10x (or more) current on psu.

Yes, in hindsight this is a great idea. Even a few volts at 0.6Ohm can fry the drive. Good point about low res pwm.

I had just finished testing the motor on a nice high end Maxon drive and was still in that plug and play mindset.