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gear, rack, helical
This gear pair model was created by the Illinois Gear & Machine Co Chicago. Cornell University acquired a set of 15 models around 1950. A similar set can be found at Ohio State University. The Cornell set has three rack and pinion models; a standard, right-angle rack and pinon, a helical rack and pinion and a worm drive and rack-gear mechanism. The rack and pinion consits of a toothed wheel that drives a straight prismatic link in a linear or straight-line motion. The rack and pinion is a three-link kinematic chain with a revolute joint, a prismatic joint [the rack] and a toothed pair higher-pair joint. In the helical rack and pinion, the teeth on the gear are helical and engage the straight rack teeth in a gradual manner. In this model, a worm screw engages both a prismatic rack below as well as the circular gear above, simultaneously generating linear motion in the rack and rotary motion in the gear. It is a beautiful model to operate and watch move.