"... While conventional paired bicycle cranksets have been around since the dawn of the bicycle and they work pretty well. However they do have one fundamental weakness. During the rotation cycle of a conventional crankset there is a point when the rider is not producing any power. On an upright this is when the cranks are straight up and down. This point varies widely on recumbents. Rotor cranks are the latest in a long line of products designed to eliminate that "dead spot". Rotors use a system of cams to make sure that your cranks never become aligned in a way that doesn't allow you to produce any power. Your feet will be at the one o'clock and six o'clock position when they would be at twelve and six on conventional cranks."