Electric RC – Outrunner vs. Inrunner
With technology continuing to develop light-weight and efficient power supplies, it’s not surprising to see an increase in popularity of the number of electric powered rc airplanes, helicopters and gliders. Combined the demand with continuing drops in cost you soon realize that electrics are a great way to get into the world of rc.
Inrunners are constructed with the magnets attached directly to the shaft, which is surrounded by the copper windings. Because the magnets are close to the shaft it spins very quickly. This means they produce high rpm but low torque. Inrunners are efficient and powerful, but need a gearbox to spin large propellers. Inrunners are best suited for use with smaller propellers for faster flying speeds.
Outrunners are constructed with the copper windings on the inside. The shaft is attached to a “bell”, or casing that contains the magnets, which spin around the copper windings. Because the extra weight of the bell and magnets are further out from the shaft it acts like a flywheel. In general, outrunners have a lower rpm but a higher torque than inrunners.
This higher torque enables an outrunner to spin a larger prop. Outrunners are best suited for larger aircraft needing larger propellers.
Another thing to note:
There is a key difference in the housing of an inrunner and outrunner electric motor. While the housing of an inrunner electric motor does not spin, the housing of an outrunner does. Therefore, an inrunner can come in direct contact to a surrounding surface and not damage it. However, an outrunner requires ample space surrounding the motor to allow the motors housing to spin.