Planetary sun gear (not shown) connects to the rotor of this pancake motor configuration.
For a given size motor, the larger the rotor, the more torque available. However, the bigger the rotor, the more wasted space inside.
Inserting a single-stage planetary gear train takes advantage of this available real estate. The result: a pancake motor measuring 80 mm in diameter and 12.5 mm thick that delivers more than 70 Newton-centimeters of torque.