What is an outrunner brushless motor

What is an outrunner brushless Motor?

Outrunner brushless motor is a type of brushless DC electric motor. T stator is mounted on the outside of the rotor. This configuration allows for a more efficient use of space, and results in a higher power-to-weight ratio than other brushless motor designs. Compare with the inrunner bldc motors, outrunner bldc motors are lighter in weight, higher in power and huger in torque. Outrunner brushless motors are typically used in applications where high power and/or speed are required.

Structure Design of Outrunner Brushless Motor

The brushless external rotor motor is mainly composed of winding coil set, permanent magnet steel, housing and bearing. The permanent magnet steel of the outer rotor motor is adhered to the housing, and the housing is regarded as the rotor and is connected to the output shaft. When the motor is running, the rotation of the outer housing of the brushless outer rotor motor drives the rotation of the output shaft. Because the mass of the rotor is concentrated on the housing, the moment of inertia of the outer rotor motor will be greater than that of the inner rotor motor. It means outrunner bldc motors are slower than normal brushless motor.

Outrunner BLDC Motor Markets Forecast

The brushless motor is becoming more and more popular in recent years because of its high efficiency, low noise, long life and other advantages.

“The global brushless DC motor market was valued at US$ 9.8 billion in 2019 and is expected to grow at a CAGR of 7.0% during the forecast period 2020-2025 to reach US$ 14.1 billion by 2025. The Asia-Pacific region is expected to be the largest market for brushless DC motors with a share of around 38% of the global market in 2019.”

The brushless outer rotor has more advantages than the inner rotor motor in terms of volume and weight. Although the price of the brushless outer rotor brushless motor is high. However, according to the market feedback, the market of the brushless outer rotor is increasing steadily every year.

Which kinds of gearbox could used on outrunner brushless motor?

The brushless outer rotor motor has a relatively low KV value, it can achieve low speed and high torque under the same voltage compare with inner rotor motor. According to the design standard, the outrunner bldc motor speed range is about 1000-20000rpm. If the application field requires lower speed and higher torque, then use of a gearbox will become a good choice.

So which kinds of gearbox could used outrunner brushless motor? Here are 3 kinds of gearbox.

Spur gearbox: Low cost spur gearbox is one of the most popular gearbox on the market. Outrunner brushless could equip spur gearbox for some applications with space requirements. Clik here for more information about spur gearbox.

Planetary gearbox: The most suitable gearbox for the outrunnber brushless motor is the planetary gearbox. Because the circular planetary gearbox can just fit the shape of the outrunnber brushless motor. Planetary gearbox has high efficiency, low noise and moderate cost. Also it can make good use of the high power and low speed characteristics of the brushless outer rotor.


worm gearbox: Worm gearboxes are relatively unsuitable for brushless outer rotors. But worm gearboxes can also come in handy in some special applications.


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