What is the difference between brushless inrunner motor and outrunner BLDC ?


Outrunner: The permanent magnets on the outrunner are placed on the rotor and the rotor spins on the outside case. On the inside of the motor are the stator windings which do not rotate, they are fixed in position.

For example:

Non-waterproof electric skateboard motors


Inrunner: On the outer side of the motor is the case. The case in this situation does not rotate and is fixed. The stator windings are placed on the inside face of the case. When you spin the motor shaft of an inrunner, you are spinning the rotor which also contains the permanent magnets much like the outrunner. The difference of course being that they are now at the center of the motor.

For example:

Waterproof brushless DC watersports motor


Performance Differences

For simplicity, let’s loosely consider motors of equal size and weight in order to compare the possible performance differences.

 

Parameter for comparison

Inrunner

Outrunner

Can Diameter

Smaller

Larger

Can Length

Larger

Smaller

RPM per Volt

Higher

Lower

Motor power

Lower

Higher

Torque

Lower Torque

Higher Torque

Efficiency

Better

 

Heat Dissipation

 

 Better

Applications

More used for efoil/surfboard/boat, RC cars, robots, etc.

More used for Electric skateboard, electric bike, e-scooter, rc drones/airplanes/cars/boat, robots, etc.