Cardan_Shaft Picture made on my own
A driveshaft or driving shaft or Cardan shaft is a mechanical device for transferring power from the engine or motor to the point where useful work is applied.
Most engines or motors deliver power as torque through rotary motion: this is extracted from the linear motion of pistons in a reciprocating engine; water driving a water wheel; or forced air or water in a turbine. From the point of delivery, the components of power transmission form the drive train.
Driveshafts are carriers of torque: they are subject to torsion and shear stress, which represents the difference between the input force and the load. They thus need to be strong enough to bear the stress, without imposing too great an additional inertia by virtue of the weight of the shaft.
Most automobiles today use rigid driveshafts to deliver power from a transmission to the wheels. A pair of short driveshafts is commonly used to send power from a central differential, transmission, or transaxle to the wheels.
In front-engined, rear-drive vehicles, a longer driveshaft is also required to send power the length of the vehicle. Two forms dominate: The torque tube with a single universal joint and the Hotchkiss drive with two or more joints. This system became known as Systeme Panhard after the automobile company, Panhard et Levassor patented it.
Early automobiles often used chain drive or belt drive mechanisms rather than a driveshaft. Some even used electrical generators and motors to transmit power to the wheels.
In British English, the term "driveshaft" is restricted to a transverse shaft which transmits power to the wheels, especially the front wheels. A driveshaft connecting the gearbox to a rear differential is called a propeller shaft and a driveshaft connecting a rear differential to a rear wheel is usually called a halfshaft. The name derives from the fact that two such shafts are required to form one rear axle.
On a power-driven ship, the driveshaft, or propeller shaft, usually connects the transmission inside the vessel directly to the propeller, passing through a stuffing box or other seal at the point it exits the hull.
As the rotating propeller pushes the vessel forward, the marine driveshaft is also subject to compression, and when going reverse, to tension.