[rotormonkey13]

There's a couple different versions of that motor with different kv ratings.

kv = rpm per volt. So you can figure out the rpm of the motor with this:

44.4v * 510kv = 22644rpm at the motor.

That's assuming a 12s battery. Since I don't know what battery setup you're aiming for or what motor you have I'm totally guessing here.

Once you know the motor rpm, you figure out what your gear ratio will be and multiply that by the motor rpm to get rpm at the main gear.

(16pinion / 170main) * 22644rpm = 2131.2rpm at the head.
Assuming a 90% motor efficiency we do this:
2131.2 * 0.9 = 1918.08

So if that's your setup (12s battery with the 510kv motor, 16t pinion and 170t main gear) then you can expect around 1918rpm at full throttle. If you want higher, then you can probably increase the timing of the motor (via ESC settings) to get a little more rpm out of it. Or go to a larger pinion (or smaller maingear) if available.

Clear as mud?

[vgjunky]

I think I got it, thanks again for all that responded to this query. I am sticking with the 4025 100kv Scorpion, but ordered a CC 100 Esc and a BEC. I will fly in 6S for the summer and get used to the heli. I am just going to be doing sport flying and very light 3D. The setup I am using seems to be a popular one for that heli but thanks to you and the others I better understand the gear ratio, pinion, battery config, esc. Man, a lot more complicated then matching and engine to a plane. lol

Originally Posted by rotormonkey13

There's a couple different versions of that motor with different kv ratings.

kv = rpm per volt. So you can figure out the rpm of the motor with this:

44.4v * 510kv = 22644rpm at the motor.

That's assuming a 12s battery. Since I don't know what battery setup you're aiming for or what motor you have I'm totally guessing here.

Once you know the motor rpm, you figure out what your gear ratio will be and multiply that by the motor rpm to get rpm at the main gear.

(16pinion / 170main) * 22644rpm = 2131.2rpm at the head.
Assuming a 90% motor efficiency we do this:
2131.2 * 0.9 = 1918.08

So if that's your setup (12s battery with the 510kv motor, 16t pinion and 170t main gear) then you can expect around 1918rpm at full throttle. If you want higher, then you can probably increase the timing of the motor (via ESC settings) to get a little more rpm out of it. Or go to a larger pinion (or smaller maingear) if available.

Clear as mud?