Leonardo da Vinci designed a crankshaft to convert reciprocating motion into continuous rotary motion.
A crankshaft uses offset crank sections to transform the back-and-forth movement of connecting parts into rotation around an axis. In a machine driven by a crank, this arrangement can also reverse the process, turning rotation into reciprocating motion.
Leonardo’s mechanical studies included crank mechanisms, cams, gears, and other ways to transmit motion. His designs were not engines in the modern internal-combustion sense, but they explored principles later used widely in pumps, mills, and vehicles.
A crankshaft is not simply a flywheel. A flywheel stores rotational energy and smooths motion, while a crankshaft changes the direction or form of mechanical movement. The two components can work together in some machines.