A transmission has a housing having a main axis with a retaining element fixed in the housing and forming a set having a predetermined number of radially extending and angularly equispaced guides. An output element rotatable in the housing about the axis is formed with an array having a number smaller than the predetermined number of radially inwardly open recesses axially adjacent the guides. An input element rotatable in the housing about the axis has a radial outer and generally circular peripheral surface centered on an axis radially offset from the main axis. Respective transmission elements radially displaceable in the guide grooves between inner and outer positions each have a shaft extending substantially parallel to the axis with a guide section engaged and radially shiftable in the respective guide groove, a driven section engageable in the recesses, and a drive section radially engageable with the input-element surface.