Cycloid speed reducer with enhanced dynamic balance

A cycloid speed reducer, comprising:

• a first roller assembly comprising a first wheel disc and a plurality of first rollers, wherein the first wheel disc has a first axial hole, and the plurality of first rollers are disposed on the first wheel disc;
• an input shaft comprising an eccentric part, wherein the input shaft is rotatable and partially penetrated through the first axial hole, and the eccentric part is eccentrically fixed on the input shaft, wherein while the input shaft is rotated, the eccentric part is eccentrically rotated about an axel center of the input shaft;
• a cycloid disc comprising an outer ring-shaped part, an inner ring-shaped part, a second axial hole and an accommodation space, wherein the eccentric part is disposed in the second axial hole, so that the cycloid disc is rotated with the eccentric part, wherein the outer ring-shaped part is located at an outer side of the cycloid disc, the outer ring-shaped part has a first outer wall and a first inner wall, at least one first tooth is formed on the first outer wall of the outer ring-shaped part, the at least one first tooth is in contact with the corresponding first roller, and at least one second tooth is formed on the first inner wall of the outer ring-shaped part, wherein the inner ring-shaped part is located at an inner side of the cycloid disc, the inner ring-shaped part has a second outer wall and a second inner wall, and the second axial hole is defined by the second inner wall of the inner ring-shaped part, wherein the accommodation space is arranged between the outer ring-shaped part and the inner ring-shaped part;
• a second roller assembly comprising a second wheel disc and a plurality of second rollers, wherein the second wheel disc has a third axial hole, the input shaft is disposed in the third axial hole, the plurality of second rollers are disposed on the second wheel disc, and each of the second rollers is in contact with the corresponding second tooth;
• and
• at least one weight element accommodated within the accommodation space, and disposed on the second outer wall of the inner ring-shaped part, wherein when the cycloid disc is eccentrically rotated with the eccentric part of the input shaft, a radial force generated by the input shaft is balanced by the weight element.