STM B-G431B-ESC1 + eBay 4108 BLDC motor or SimpleFOC Mini + 2208 90kv BLDC motor

hardware support
1

I’m thinking of getting in on the FOC game but I’m debating what controller + motor combo to use, I found some high torque low kv brushless motors on eBay (4108 motors) but they seem to be designed for drones. (with a stated internal resistance of .1932 ohms, WAY less than the 10 ohms stated here) Since they can pull up to 6.4A at 11V (40 amps according to worst-case calculations using the stated resistance value) this seems like quite a bit too much for the mini to handle. The alternative is to use a 2208 90kv BLDC motor but I can’t find much information online about them and they seem to be quite a bit weaker than the 4108’s. If anyone has experience with the 2208 90kv motors please let me know.

In summary, I don’t think the SimpleFOC Mini would be able to handle a 4108 motor without blowing up, it seems like I’d have to go to the STM B-G431B-ESC1 to be able to handle this motor.
If anyone has experience with the 2208 90kv it seems like this motor would be a better match for the SimpleFOC Mini, but would it be possible to extract around ~.5 Nm peaks from it at 11.1v?

2

Those small motors have a phase resistance around 10 Ohm. At 1A per pase (I^2*R) that’s ~15W of resistive heat, you’d need pretty good airflow or low duty cycle not to melt the motor windings.

The bigger motors get less hot. Not only are they more torquey due to their larger size, they also have more surface area which helps to get rid of the heat. It really depends on how much torque/work you need.

The B-G431B is capable of handling between 10A to 15A continuous without airflow (depends on pwm freq). Not sure about the simpleFOC mini, the docs state “up to 2.5A”. For a 90kv motor this translates to only ~0.23Nm. (Kt ≈ 8.27 / Kv = 0.09 Nm/A). 3D printed gears might help here.