Early steam engine designs of the 18th century used the unwrapping of a cable from a curved sector at the end of a lever arm to produce a straight-line motion of the piston. This version of such a mechanism was designed by Franz Reuleaux and was based on the mathematical cycloid curve that is generated when a circle rolls on a straight line. It is interesting that Reuleaux made a straight-line model based on his own invention as well as the fact that he produced models of 39 straight-line mechanisms in the Voigt collection even though his two major books did not explicitly treat such devices.

Francis Moon 2004-07-00