Movement No. 123 is an ingenious substitute for the crank, converting reciprocating rectilinear motion of a double rack into continuous rotary motion of a center gear. The double rack moves back and forth, its teeth engaging alternately with two semi-circular toothed sectors positioned on either side. Each toothed sector has a spur-gear attached to it, and these spur-gears mesh with a central output gear. A curved piece on the center gear catches two stops on the rack at each end of the stroke, which mechanically switches engagement from one toothed sector to the other — ensuring that whichever direction the rack moves, one sector is always driving the center gear in the same rotational direction. This clever sequencing of sector engagement produces continuous, unidirectional rotation from a simple back-and-forth linear input, functioning as a fully mechanical crank substitute.
123. Intended as a substitute for the crank. Reciprocating rectilinear motion of the double rack gives a continuous rotary motion to the center gear. The teeth on the rack act upon those of the two semi-circular toothed sectors, and the spur-gears attached to the sectors operate upon the center gear. The two stops on the rack shown by dotted lines are caught by the curved piece on the center gear, and lead the toothed sectors alternately into gear with the double rack.