What Igor said, with a different spin:
Motor designers have a wide latitude to set the kV of a motor. Nothing's ever quite so simple, but to a first approximation, as long as you fill the available space with the same amount copper, you can use just a few turns of thick wire, or lots of turns of thin wire, and get pretty much the same power, torque, and speed out vs. power in. The difference is that a motor that uses one humongous turn in each slot will have 10 times the kV of a motor that uses ten smaller turns, so it'll use 1/10th the voltage -- but it'll need ten times the current to generate the same power, torque & speed.
This is why you can get your vintage 1950 Ford's starter and generator rewound to 12V -- they replace the existing wire with wire that has half the area, and fill the space with twice as many turns (don't forget to change the regulator, though).
Fewer turns (and higher kV) means more current, which means bigger wires, and fewer, higher capacity cells. More turns (and lower kV) means less current, which means smaller wires and more cells. This is good because of the smaller wire, but bad because it complicates ESC design (there's a threshold at around 20V where you have to change the way you drive the MOSFETs; there's a different, lower, softer threshold that has to do with how the on-board battery eliminator circuit is designed). It's these good vs. bad tradeoffs in the ESC and wiring that drive the choice of kV, more than what the actual motor demands.
Topic: kV ratings. (Read 1185 times)
