[suicideneil]

I think it would be possible, but you'd need to run the motor at max throttle with any given voltage ( lower the better really ), then get an accurate rpm reading. Then its just a bit of simple maths to determine rpms per volt = kv rating. Thats assuming there isnt any voltage drop, but without any load on the motor ( bench test as such ) there shouldnt be really, or not much anyway.

Famous last words....