Wave reducers with rolling elements are a class of speed reducers that transmit motion through a wave-like profile interacting with intermediate rolling elements, such as balls or rollers. Instead of using gear teeth like planetary or cycloidal drives, they rely on pure rolling contact to achieve high reduction ratios, low backlash, and compact size. The eccentric cam pushes the rolling elements against a specially shaped rigid ring, causing smooth, high-ratio relative motion between input and output.