Abstract: A drive linkage is provided between a drive shaft and a driven shaft, each being rotated on a fixed axis. The linkage includes a pair of intermediate gears between gears mounted concentrically on the drive and driven shafts, respectively, with links fixing the center-to-center distances of adjacent gears and maintaining neighboring gears in driving engagement. The linkage further includes a pair of control gears, a primary control gear being maintained in driving engagement with the drive gear through a pivotally mounted link, and a secondary control gear linked to the primary control gear and rotatably mounted to one of the intermediate gears through a pin near but offset from the centers of these gears. A selective positioning of the primary control gear causes an oscillation in the intermediate gear engaged with the driven gear, resulting in cyclical accelerations and decelerations in the driven gear responsive to a constant rotational speed in the drive gear.