The K-H-V type planetary gears with cycloid gears have been used in an industrial robot and a machine requiring precise positioning. The rotational transmission error of the K-H-V type planetary gears with cycloid gears should be as small as possible in order to apply these planetary gears in various industrial fields. In this paper, the K-H-V type planetary gears with cycloid gears and three crank shafts were transformed into a two-dimensional model with twenty degrees of freedom, in a plane perpendicular to the input and output shafts, and the manufacturing and assembly errors were also transformed into the equivalent error so as to determine the rotational transmission error. Using the model and equivalent error, the theoretical rotational transmission error was analyzed, and agreed relatively well with the measured one.
