Just wanted to share what I've learned the hard way. Higher motor pole count means higher electrical RPM (i.e. eRPM). Actual rpm is calculated be eRPM divided by the number of pole pairs in a motor. So if you have a 4 pole motor (2 pole pairs) running at 80,000 eRPM, you'd be turning 40,000 actual rpm (80,000/2 pole pairs).
Why is a high pole count good? On paper, that allows for increased efficiency because there's less "dead space" in the stator - space that's not being used for motor windings. When all else is the same, the motor with more poles has a lower kV and potentially higher torque.
Why is a high pole count bad? For what we're doing this is pretty important, and it has to do with ESCs. The power stage of ESCs are almost always composed of MOSFETs. A MOSFET is basically a transistor, but instead of being current driven, it's voltage driven. As such, a MOSFET has input, output and reverse transfer capacitances, all of which must be taken into account.
I'll try not to go too far into the weeds; but a discharged capacitor looks basically like a short circuit to a DC voltage (limited only by the ESR of the capacitor - equivalent series resistance, anyway). Which means there's a tremendous burst current until those "capacitors" are charged every time the MOSFET switches (especially on the output side of the MOSFET, which usually has no current limiting, since we want the motor to get as much power as possible). These current spikes are what are known as "switching losses."
Once you really understand the above paragraph, it's easy to see that a 2 pole motor (i.e. 1 pole pair) will incur MUCH LOWER switching losses in an ESC than a 6 pole motor (3 pole pairs), since the 2 pole motor's ESC only needs to hit 100,000 eRPM to hit 100,000 actual rpm, where the 6 pole motor would need 300,000 eRPM - 3 times as much; meaning 3 times the switching losses.
Until we replace MOSFETs with a transistor with no output capacitances, this will remain something we need to keep an eye on.
Why is a high pole count good? On paper, that allows for increased efficiency because there's less "dead space" in the stator - space that's not being used for motor windings. When all else is the same, the motor with more poles has a lower kV and potentially higher torque.
Why is a high pole count bad? For what we're doing this is pretty important, and it has to do with ESCs. The power stage of ESCs are almost always composed of MOSFETs. A MOSFET is basically a transistor, but instead of being current driven, it's voltage driven. As such, a MOSFET has input, output and reverse transfer capacitances, all of which must be taken into account.
I'll try not to go too far into the weeds; but a discharged capacitor looks basically like a short circuit to a DC voltage (limited only by the ESR of the capacitor - equivalent series resistance, anyway). Which means there's a tremendous burst current until those "capacitors" are charged every time the MOSFET switches (especially on the output side of the MOSFET, which usually has no current limiting, since we want the motor to get as much power as possible). These current spikes are what are known as "switching losses."
Once you really understand the above paragraph, it's easy to see that a 2 pole motor (i.e. 1 pole pair) will incur MUCH LOWER switching losses in an ESC than a 6 pole motor (3 pole pairs), since the 2 pole motor's ESC only needs to hit 100,000 eRPM to hit 100,000 actual rpm, where the 6 pole motor would need 300,000 eRPM - 3 times as much; meaning 3 times the switching losses.
Until we replace MOSFETs with a transistor with no output capacitances, this will remain something we need to keep an eye on.