[Animats]

How high a frequency do you have to inject for sensing? Much higher than the power chopping frequency, presumably. Megahertz? Harmonics from the PWM drive are going to interfere. I can see why separating signal from noise is a problem, and why mating a motor and a controller isn't going to be plug and play.

Larger drone prop motors seem to be mostly permanent magnet brushless. Often the stator is on the inside, and the rotor is a rotating shell carrying permanent magnets that fits over the stator. 12 coils and 14 permanent magnets is a common configuration.

Other drone motors look more like standard motors, with an outside stator and an interior rotor. Some of those are definitely permanent magnet.

Here's a good overview.[1] If you wanted to repurpose such motors for industrial control, the main problem would be cooling. They're intended for use with the prop blowing air through them, so they can dissipate much more heat than most motor configurations. Slow speed, high-torque operation would probably overheat them.

[1] http://www.barnardmicrosystems.com/UAV/engines/electric_moto...

[stevendhansen]

The high freq signal has to be lower than the switching frequency - otherwise you end up with harmonic interference from the PWM like you mentioned. For high performance servo control in the 5-200kW range with switching frequencies up to 20kHz I typically see high frequency injection in the 1-4kHz range. This is high enough to produce negligible torque ripple and minimal estimation error, but low enough to be synthesizable without an ultra high PWM frequency. Of course for smaller systems switching at 100s of kHz or even MHz a higher high frequency signal could be injected.

I suspect that this type of sensorless strategy will become more popular with the rise of GaN and SiC devices, but it is currently implemented with good results today using only standard Si IGBTs and MOSFETs.