Outer Rotor Brushless DC Motor Solution

Whether outer rotor motor or inner rotor motor, they are both Brushless DC Motor. As two types of BLDC, their difference is only in design.

The brushless DC motor consists of a rotor and stator. As a rotating part, the rotor has rotor magnets, while the stator serves the role of the station and has stator windings.

In terms of inner rotor motor, the rotor is located in a wound stator. But contrary to conventional brushless DC motor, for the external rotor motor, the rotor rotates around the internal stator.

Compared with the inner rotor design, the outer design has the following advantage:

As we know, the size of the rotor is direct proportional relation to the value of inertia. The bigger the rotor, the greater the inertia. While this means that the problem of torque ripple can be solved. Also, this is an ideal solution to the applications that require smooth and stable operation at low speed.

For outer rotor motors, they have higher torque than inter rotor motor. Because the torque equation is that magnetic force times the radius of the air gap, which is also be called the length of magnetic flux. That is to say, the bigger the air gap, the higher the torque. Generally, the external rotor motor can be designed with a larger area than the inner rotor. Also, the larger diameter of the outer rotor means the rotor can accommodate more poles, which increases magnetic flux.

During the development process, to adapt to different environments and requirements(which need to use encoder), I.CH designs two types of outer rotor motor:

(1) Outer Rotor BLDC Motor + Coaxial Encoder

(2) Outer Rotor BLDC Motor + Off-axial Encoder