ORIGINAL: Broken Blade
Hi,
I'm shopping for brushless motors for a Trex 450 and looking at motors with KV's anywhere from 3100 to 4000. Does that mean the higher KV would need a smaller pinion to get the same head speed as a lower KV with a larger pinion? What does KV actually mean? Thanks
KV is the spec that tells you what RPM the motor is designed to give power volt fed into it.
A 4000 KV motor will turn at 44,400 rpm if powered by an 11.1V 3S battery pack.
So a 3100 KV motor will turn slower at 34,410 rpm with the same 11.1 volts input.
The gear ratio of the heli will determine the rotor speed relative to the motor speed. The gear ratio is the ratio of the number of teeth on main gear relative to the number of teeth on the pinion.
So as you can see, you will have to change pinions to get the same rotor speed from one with the other. As you stated, you would have to use a lower tooth count pinion on the 4000KV motor in order to get the same rotor speed as the 3100KV motor on a pinion with a higher tooth count.