Grades 3–5 · Machines
How does a rack and pinion turn rotation into straight movement?
A rack and pinion connects turning motion with straight movement. The pinion is a round toothed wheel. The rack is a straight bar with matching teeth, held by a guide so it can slide along a straight path.
In the diagramA round pinion drives a straight rackPinionRack12 teeth • 5 mm per tooth0.25 turn counterclockwise15 mm travel right
When the pinion turns, its teeth press against the rack's teeth. Each passing tooth advances the rack by one tooth spacing. In this illustration, a 12-tooth pinion works with teeth spaced 5 millimeters apart. One full turn therefore moves the rack 60 millimeters. A quarter-turn moves it 15 millimeters.
Changing the turning direction changes the rack's travel direction. With the pinion above the rack as shown, counterclockwise turning moves the rack right. The connection depends on teeth staying engaged without slipping. Real mechanisms also need guides and suitable tooth shapes; the picture shows their motion relationship, not how much force the parts can carry.
About this explanation
Starting knowledge: Recognize gear teeth and use small whole-number products and simple fractions.
Sources
- LEGO Education — Gear: Rack and Pinion Gearing