The Ragonnet power reverse, patented in 1909, was a true feedback controlled servomechanism. The power reverse amplified small motions of reversing lever in the locomotive cab made with modest force into much larger and more forceful motions of the reach rod that controlled the engine cutoff and direction.Eugine L. Ragonnet, Controlling Mechanism for Locomotives, U.S. Patent 930,225, Aug. 9, 1909. It was usually air powered, but could also be steam powered.Jacob H Yoder, Locomotive Valves and Valve Gears, , Van Nostrand, New York, 1917; page 131. The term servomotor was explicitly used by the developers of some later power reverse mechanisms.Lincoln A. Lang, Servo Motor Mechanism, U.S. Patent 1,480,940, Jan 15, 1924. The use of feedback control in these later power reverse mechanisms eliminated the need for a second cylinder for a hydraulic locking mechanism, and it restored the simplicity of a single operating lever that both controlled the reversing linkage and indicated its position.
