An epicyclical drive having a generally flat, disk shaped flywheel, a flywheel to pinion carrier in the form of an inner hub of the flywheel, and a flywheel support bearing and structure incorporated into the flywheel itself, all of which are concentric about a rotational axis of the flywheel so as to be axially compact, and so as to be particularly well adapted for being located beneath, or incorporated into, the floor of a grain header of an agricultural harvesting machine, for reciprocatingly driving knife knives of a sickle thereof. In particular, the flywheel support bearing is located in an annular space between the inner hub and an outer flange which is rotated by a belt or other drive for rotating the flywheel.