Cycloidal Gear Drive

What is a cycloidal gear drive?

A cycloidal gear drive, also known as a cycloidal gear, or a cycloidal speed reducer, is one type of gear that strengthens output torque while reducing speed. The operating principle of a cycloidal gear drive can be derived from that of the cycloid, which results in the naming of this device.

A gear drive is a necessary element in applications where motion transmission influences the smoothness of operation. One common example is in the transmission system in a car. The motor, which is the most important component for motion driving, facilitates the engine to drive the wheels. During this process, the speed and torque determine the performance of the car. In other words, the coordination between speed and torque and the stability of each parameter defines how well a vehicle performs. 

In order to optimize the speed and torque that the transmission system produces, the manufacturer would apply a gear drive within the system. The gear drive is connected to the motor with the output shaft, which directly transmits the regulated driving force as the car is running. Through the interaction of the teeth between each gear, the speed of motion is reduced, and the torque is thereby increased.

Depending on the arrangement of each mechanism and other factors, the gear drives or speed reducers come in a variety of forms. Among all these gear drives, the cycloid gear drives are suitable for slow rotation transmission due to their special design and operating principle. In this article, we will discuss the structure, basic function, and arrangement of the cycloidal gear drive.

How does a cycloidal gear drive form?

Similar to other types of gears, the cycloidal gear drive transmits motion from the input to the output, and this is realized with the assistance of the rotary shafts. The rotary shafts penetrate through the other components and are responsible for delivering driving force when they rotate. The components in a cycloidal gear include the eccentric shaft, bearing, cycloidal disc, pin disc, and fixed ring pins.

Eccentric shaft

The eccentric shaft is the input shaft, which rotates first when the gear drive is actuated, in order to drive other parts. It is secured by the bearing and set in the middle of the cycloidal disc and pin disc.


The bearing is set around the edges of the eccentric shaft, which is used to reduce friction produced as the shaft rotates.

Cycloidal disc

The cycloidal disc is the main disc that is equipped with teeth around the edges. On the inside of the disc, there are several holes where the roller pins protrude and rotate through.

Pin disc

The pin disc contains several roller pins that protrude through the holes on the cycloidal disc. It is attached beside the cycloidal disc and has an output shaft on the other side, which transmits the driving force with regulated speed and torque.

Fixed ring pins

The fixed ring pins are arranged around the outer part of the gear drive, which allows the teeth of the cycloidal disc to rotate along with them. In addition, the number of the fixed ring pins is bigger than that of the teeth on the cycloidal disc, so as to achieve the requirement of speed reduction.

How does a cycloidal gear drive work?

When it comes to the operating principle of a cycloidal gear drive, it derives from the principle of cycloids. The principle of cycloids is constructed as one circle rolls around the inside or outside of the base circle. The curve created as the circle rolls on the outside is called an epicycloid, and the curve created on the inside is a hypocycloid.

When a cycloid gear drive is actuated, the eccentric shaft rotates in the middle and drives the cycloid disc and pin disc afterward. Once all the components are driven, the cycloid disc rotates with the teeth interacting with the fixed ring pins. Then, the pin disc is facilitated to transmit the driving force to the application from the output shaft.

Applying the above principle in the cycloidal gear drive, the epicycloid is made when the fixed ring pins allow the cycloid disc to rotate around the intervals between each pin. In contrast, the hypocycloid is made when the roller pins on the pin disc rotate through the holes on the cycloid disc.

In some cases, the cycloid gear drive would be equipped with two cycloid discs. This arrangement allows two base discs to rotate at the same time, which doubles the effect this gear drive makes for its application. In other words, it is more effective in reducing speed and increasing torque.

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