A variable speed changing gear has an internal friction wheel made of elastic material and a cycloid wheel inscribed to the internal friction wheel. The cycloid wheel is rotated for circulating along the internal friction wheel. Because of the elastic material, the effective radius of the internal friction wheel is changeable by giving force to the cycloid wheel in the radial direction. The circulation speed of the cycloid wheel is changed in reverse proportion to the radius. The output shaft can be rotated with variable speed following to the circulation of the cycloid wheel. This speed changing gear can be operated as a load compensating device.

A continuously variable transmission has an input shaft rotatably mounted to a frame. Plural output wheels are located around the input shaft and are rotatably mounted to the frame. The output wheels have respective axes of rotation that lie in a plane, which plane is generally perpendicular to the axis of rotation of the input shaft. Each output wheel has an arcuate circumferential surface. The output wheels are arranged around the input shaft so that the innermost portions of their circumferential surfaces form a traversing path around the input shaft. The input shaft has one or more drive rollers coupled thereto so that the drive rollers can both rotate and pivot independently of the input shaft. As the input shaft rotates, the drive rollers traverse the traversing path. A slide assembly is mounted on the input shaft and is linked to the drive rollers so as to vary the orientation of the drive rollers relative to the traversing path, wherein the speed ratio between the input shaft and the output wheels can be controlled.