Outrunner

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An outrunner is an electric motor having the rotor outside the stator, as though the motor were turned inside out. They are often used in radio-controlled model aircraft.

This type of motor spins its outer shell around its windings, much like motors found in ordinary CD-ROM computer drives. In fact, CD-ROM motors are frequently rewound into brushless outrunner motors for small park flyer aircraft. Parts to aid in converting CD-ROM motors to aircraft use are commercially available.

Usually, outrunners have more poles, so they spin much slower than their inrunner counterparts with their more traditional layout (though still considerably faster than ferrite motors, when compared with motors that use neodymium magnets) while producing far more torque. This makes an outrunner an excellent choice for directly driving electric aircraft propellers since they eliminate the extra weight, complexity, inefficiency and noise of a gearbox. Some front loading direct-drive washing machines use an outrunner motor.

Outrunner motors have quickly become popular and are now available in many sizes. They have also become popular in personal, electric transportation applications such as electric bikes and scooters due to their compact size and high efficiency. ^[1]