yeah I know what he meant by a starter motor, but that cost more to get delivered here than a purpost built AC motor would.

And you wrote "of" instead of "off". Makes a lot of difference in meaning to that sentence. :)

I already have a million power supplies and batteries anyway, dont need any of that.

Hmm... RC parts are looking less and less attractive.

Does anyone know how to figure out the rpm of an electric brushed DC motor run at a given voltage, if you already know it at some other voltage?

The motor in question is http://secure.oatleyelectronics.com/...roducts_id=189 - it's 2500rpm at 36V, but I would run it at 24V. I'm fairly certain the relationship isn't linear like with brushless motors.

Cheers.

The relationship is still linear, you just have to account for loaded vs unloaded speeds.