The drive has an input rotatable about an upstanding rotational axis and carries a cam followed by a pivot arm pivotable about an upstanding pivotal axis. A power source is connected in rotatably driving relation to the input. The pivot arm connects to a knife assembly of a sickle. The input, cam and pivot arm are generally flat, and the power source is vertically coextensive therewith for incorporation in or below the floor of a header of a plant cutting machine. Rotation of the input causes offset movement of the cam about the rotational axis, resulting in sideward pivoting of the pivot arm and sickle knife. A second cam drive can oppositely drive a second sickle knife, such that opposite forces generated by operation of the drives will be largely canceled.
