Crankshaft

A crankshaft is a rotating shaft carrying one or more offset crankpins that convert the reciprocating, back-and-forth motion of pistons, delivered through connecting rods, into rotary motion, or run the same conversion the other way to turn rotation into a push-pull stroke. The earliest known step toward the mechanism appears in Baghdad in the ninth century, where the three Banu Musa brothers described automated crank devices in their Book of Ingenious Devices, a design that could not yet complete a full rotation but needed only a small modification to become a true crankshaft. The Artuqid engineer Ismail al-Jazari, who lived from 1136 to 1206, described an actual crank-and-connecting-rod system built into two of his water-raising machines, giving the crankshaft one of its earliest confirmed working forms centuries before it became standard equipment in the reciprocating steam and internal combustion engines of later ages.