Abstract: A propulsion system for converting rotary motion of a pair of weighted rotor arms into linear motion includes a support frame with a drive unit mounted thereto. The drive unit includes a rotatable shaft with a pair of rotor arms pivotally mounted thereto. Upon rotation of the shaft the rotor arms rotate about the shaft. A cone surrounds the rotor arms so as to present a course for rolling movement of the weight elements on said rotor arms. The cone is mounted to a platform which is pivotally mounted to said support frame. Upon movement of said platform and associated cone from a horizontal position the interior surface of the cone presents an asymmetrical course for the weight elements about said shaft. Upon rotation of the shaft the travel of the opposed weight elements through said asymmetrical course produces a resultant linear force on the cone which is transferred to the object attached to the support frame.