A basic Geneva Mechanism, as is commonly employed in motion picture projectors, is described in U.S. Pat. No. 1,774,789. In general, a Geneva Mechanism is used to convert uniform rotary motion to incremental rotary motion. Typically, such a mechanism includes a star wheel having a plurality of radially extending straight slots spaced equally around the periphery of the star. Interposed between these slots are concave cam guide surfaces, which, like the slots, are uniformly dimensioned and arranged. A driver component, comprised of a restraining cam, a drive arm extending from the base of the cam, and a drive pin near the far end of the drive arm, is employed for indexing the star wheel. The restraining cam has a side cam surface, which is convex and configured to interact with the concave cam guide surfaces of the star wheel. The close contact of this convex cam surface to the concave cam guide surfaces restrains the star wheel from experiencing rotary motion except during the periods in which the star wheel is driven by the drive pin. The star wheel is thus restrained intermittently, and in a manner such that the straight slots sequentially receive the drive pin.