RC-Monster Forums - what is inrunner and outrunner?

Inrunner motors have fixed windings on the inside of the can and a magnet on a shaft(rotor) that spins, like an inside out brushed motor.

Outrunners have a center piece called a stator that the windings are on. The fixed end of the motor holds the stator in place and the other end is made up of a "can" with the magnets on the inside that fits around the stator. Drive is taken of the end of the can, or a shaft fixed to the can that runs on bearings that are placed on each end of the stator.

Generally the outrunner has a lower kv and more poles than an inrunner. It is suited to and generally used in direct drive prop applications in planes. If inrunners are used in planes they generally have a gearbox that reduces the motor rpm to turn the prop. This is to make up for the lack of torque compared to an outrunner.

Inrunner motors can turn higher rpm, mostly due to their construction. Also, brushless esc's can spin a 2 pole inrunner faster than a 6 pole, due to the need for 3 times the firing pulses for the 6 pole. Hope this helps!