Motor rpm

Can someone explain.
QS 205 50H 72v, kv 24x5 650rmp, is this the maximum rpm? With or without load?
Which rpm would best to run continuously with load?

(I will calculate for the right diameter to my wake-winch drum)

Generally any RPM listed for a motor is for the voltage it is listed at. A different voltage will give a different RPM at full throttle.

If a kV is listed, then that is RPM per volt, so you can figure out the RPM it will spin at any particular voltage (unloaded), or the voltage you need to reach a certain RPM. You can calculate the kV from the other info if no kV is listed.

If none of that info is listed for a motor, you'd either have to get that info from the manufacturer, or get one and test it.

kV is 9.03 x 72V so my max rpm is 650 at load and also unloaded?

Varabou said:

kV is 9.03 x 72V so my max rpm is 650 at load and also unloaded?

Click to expand...

That will depend on what the load applied is.
What you need is to figure out how much Torque you are going to need, and then reference that to a Torque/rpm curve for that motor, at that voltage.
Ask the supplier for the Torque curve....or search on line for one ?

Varabou said:

kV is 9.03 x 72V so my max rpm is 650 at load and also unloaded?

Click to expand...

Kv is the voltage constant of the motor, which means with the pack voltage at 72, the bare motor without any load (even the air resistance a tire) in the air will spin at 650rpm at 100% throttle. As load increases, rpm at full throttle decreases, and current increases with the increased torque demand of higher loads.

Kv is inversely related to a motor's Kt, torque constant, the amount of torque it makes per amp supplied. 9.55/Kv = Kt in Nm, so that motor will produce just over 1 newton-meter of torque per amp applied, or 0.78 foot-pounds per amp.

Our hubmotors are limited by their ability to shed heat, and in their designed rpm range a hubmotor's heat comes primarily from heat losses in the copper due to resistance. That means they are happiest at high rpm, since current is lower and heat in the copper goes up with the square of resistance. I'd make my design flexible so that if I ran into heat problems I could solve it with the bottom part of the motor in a water bath.

You should message Bzhwindtalker, who has built a wake-winch using a hubmotor, though he used a less capable motor than the one you mentioned.

Since your gearing is variable, if you haven't already purchased your motor, I would suggest choosing one with a higher Kv. That's because their lower copper resistance means they can run at higher power for a given voltage.