What is a Cycloidal Speed Reducer?

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As the eccentric bearing turns one revolution, the cycloidal disc advances in the opposite direction by (360/L) degrees or (P/L) pitches of pins/rollers. (Figure 3)  The output direction of cycloidal reducer with single stage reduction equals to the opposite of input direction.

In order to convert the wobbling motion of a cycloidal disc into the smooth concentric movement of output shaft, several output shaft rollers are placed inside the small circles of a cycloidal disc.  These rollers are also attached to the output shaft pins.  The difference (2C) between the diameter of output shaft roller and the small circle is exactly twice the eccentricity (C) of eccentric bearing.  This distance (2C) is also the radial difference between the valley and crest of a cycloidal disc lobe. (Figure 4)

With the arrangement above, the mechanism is capable of converting the rocking motion of an eccentric bearing into the wobbling planetary motion of a cycloidal disc.  This motion is then transformed to the smooth concentric movement of output shaft through the output shaft rollers.  The speed reduction is achieved, and torque transmission is accomplished.