Depending on how the transmission ratio intervenes, the output shaft of the gearbox, also called the secondary shaft, can rotate at more, less or the same revolutions as the crankshaft.

The crankshaft is a set of cranks that together with a series of connecting rods transform the reciprocating movement into circular or vice versa. Each crank consists of a part called the crankpin and two arms that end on the rotating shaft of the crankshaft.