An improved Waddington drive is positioned within a hub, such as a bicycle hub, and connected between the hub and an operator-powered sprocket. A series of planet gears are journaled for rotation in the rotating hub and all engage a fixed sun gear on a mounting shaft. The planet gears are connected by means of one-way clutches to a series of followers which engage a cam mounted on the sprocket so that it has a variable eccentricity. A coiled spring connected between the input sprocket and the cam varies the eccentricity in response to the torque reaction forces between the cam and the followers. This maintains the input-output ratio of the hub at a value enabling constant input torque irrespective of variations in output torque requirements.
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