A mechanism, e.g. for driving a wheelchair, converting oscillating motion of a lever (15) into rotary motion of an output disc (capstans 34) by means of a flexible member (belt 26). In one direction of the lever (15), the belt (26) drives the output disc (capstans 24). In the other direction, the belt (26) slips. This is achieved by a (rotary) drag element (22) providing a (rotary) resistance force (=counter force) upstream the output disc (34) thereby tensioning the belt (26) such that slip is avoided.
