Pinion

A pinion is a round gear—usually the smaller of two meshed gears—used in several applications, including drivetrain and rack and pinion systems.

Applications

Drivetrains usually feature a gear known as the pinion, which may vary in different systems, including

the typically smaller gear in a gear drive train (although in the first commercially successful steam locomotive—the Salamanca—the pinion was rather large).^[1] In many cases, such as remote controlled toys, the pinion is also the drive gear for a reduction in speed, since electric motors operate at higher speed and lower torque than desirable at the wheels. However the reverse is true in watches, where gear trains commence with a high-torque, low-speed spring and terminate in the fast-and-weak escapement.
the smaller gear that drives in a 90-degree angle towards a crown gear in a differential drive.
the small front sprocket on a chain driven motorcycle.
the clutch bell gear when paired with a centrifugal clutch, in radio-controlled cars with an engine (e.g., nitro).^[2]

Rack and pinion animation

In rack and pinion systems, the pinion is the round gear that engages and moves along the linear rack.

^ Gear Nomenclature, Definition of Terms with Symbols. American Gear Manufacturers Association. 2005. p. 72. ISBN 1-55589-846-7. OCLC 65562739. ANSI/AGMA 1012-G05.
^ Eric Perez. "Clutch Tuning". NitroRC.com. Retrieved 2010-01-29.^{[dead link]}

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