RPM per Volt??
 

What exactly does the kV mean in electric motors?

3600kV, 4200kV, 5100kV? What's the difference?

Does it mean they turn faster per volt, or that they turn at the same speed, but use up more voltage?

RE: RPM per Volt??
 

Kv refers to the ratio of the RPM to the Voltage at the motor's terminals minus the Voltage loss inside the motor due to the coil's resistance Rm.

Kv = RPM / (Vin - Vloss)
Thus:
RPM = Kv * (Vin - Vloss)

Vloss = Iin * Rm,
So, the RPM will decrease as the current Iin (load) increases.
If a larger propeller is used the current will increase, thereby decreasing the motor's RPM.