Gear drive having continuously variable drive ratio

A variable drive ratio transmission including a support, a first shaft rotatably mounted to the support so that the shaft can rotate about a first axis, a helical rack supported by the first shaft so that the rack has a plurality of toothed convolutions spaced apart along the first shaft, the diameters of said convolutions being such that together they define an imaginary conical envelope encircling the first shaft, a second shaft rotatably mounted to the support so that the second shaft is spaced from and extends parallel to said envelope, and a gear member mounted to the second shaft for rotation therewith, said gear member including first and second similar pinions having teeth to mesh with those of the rack, said gear member being slidable along the second shaft so that the gear member may be positioned at any location along the rack, wherein said pinions are rotatable through small angles relative to the shaft and relative to each other, first resilient means bias said first pinion to a home angular position on the shaft, and second resilient means bias said pinions relatively toward a home position wherein their teeth are in alignment.