Early models found in China dating back to the Western Han dynasty (202 BC - 9 AD) were used for winnowing fans and grinding grain.

Here is a detailed write-up on the mechanism and applications of a crank. 1.

A is a fundamental mechanical component—an arm attached at a right angle to a rotating shaft—used to convert circular motion into reciprocating (back-and-forth) motion, or vice versa. It is a cornerstone of mechanical engineering used to manually or mechanically turn axles, powered by either human effort or engines.

A crank consists of a crank arm (or web), a shaft (or axle), and a crank pin.

Cranks can be powered by hand (e.g., a winch) or foot (e.g., a bicycle pedal). 2. Key Examples & Applications