Using a motor with unknown pole pairs, kV, etc

I’ve recently come into possession of a large rover platform that’s currently driven by two mystery meat BLDC motor drivers that I’d like to replace with ODrives. The problem is that I know nothing about the motor driving the system, there’s no markings of any kind, and the supplier doesn’t have any information for me.

Is there any way for odrive to figure out the pole pairs/kV or some way I could figure it out with a multimeter/oscope/etc?

To make matters more difficult, the motor is permanently attached to a worm gear drive so any tests directly on the motor might not be feasible.

Any thoughts on how I could approach this? Thanks!

Hi! Definitely things you can do to figure this out. First question – what sort of encoder do you have on it? Anything incremental/absolute, or halls only?

If you have anything but halls on there, you can just put an arbitrary number of pole pairs, try to calibrate it, and then (assuming you’re using an ODrive Pro/S1 in the GUI) the ODrive will complain and suggest the value it thinks is correct :slight_smile:

KV is mostly just a scaling constant in the ODrive firmware (there’s a few things that require accurate KV, basic/typical control does not), so that can definitely be eyeballed. Easiest way is to just see the maximum speed you can spin the motor – with an ODrive Pro kv=speed/supply_voltage, and with an ODrive S1 kv=speed/supply_voltage * 1/0.78

excellent, thanks for the advice! It’s just halls unfortunately. Could I still guess and check with halls until it works? I know the gearing ratio of the worm drive, if I can get things running and count hall increments maybe I can back out how many hall increments per motor revolution, but I’m not quite sure how to go about that.

Well, if you have halls then the ODrive actually won’t know if your pole pairs estimate is wrong or not! It’ll be happy to calibrate, and then you can try e.g. commanding 1 rev/s then you can measure how long it takes the output shaft to turn, etc etc.

Great! I was worried the odrive calibration wouldn’t run at all if there was a mismatch. Thanks very much! New Odrives are ordered and on their way, we’ll be much happier to have the improved control.

Awesome! Let me know if there’s anything I can help with!