In internal rotor motors, the rotor with the permanent magnets rotates on a shaft inside a stationary stator with coils. Their benefits lie in their lower rotor inertia and their better dissipation of heat losses. They are particularly suitable for high speeds.
Outer rotor motors are shorter than internal rotor motors and offer a cost-effective solution particularly for large series. In these motors the permanent magnets are mounted on the rotor housing which rotates around the internal stator with the windings. Thanks to the higher inertia of the rotor, external rotor motors have a lower torque ripple than internal rotor motors.