Reducer

A reducer, comprising:

• a casing having an inner circumferential wall provided with a first limiting part;
• an internal ring gear arranged in the casing and having an outer circumferential wall provided with a second limiting part, the first limiting part being fitted with the second limiting part to limit rotation of the internal ring gear;
• and
• an elastic cushion having at least a portion located between the first limiting part and the second limiting part and abutting against the first limiting part and the second limiting part in a radial direction of the internal ring gear,
• wherein the first limiting part is a first projection, the second limiting part is a second projection, the second projection defines a snapping slot in an end face of the second projection away from the internal ring gear in the radial direction of the internal ring gear, the snapping slot extends in an axial direction of the internal ring gear, and the first projection has at least a portion located in the snapping slot.