Why do you need universal coupling?

Answer 1

Assuming you are asking about the universal couplings (joints) in the drive shaft, these joints are needed because the engine is fixed to the vehicle's chassis (frame) whereas the wheels are suspended from the chassis. This means that the wheels able to move relative to the engine and transmission, so there must be a mechanism that accomodates this movement. This is most commonly done with u-joints in the driveshaft on rear-wheel or four-wheel drive. On front-wheel drive, this is often done with CV-joints.

Answer 2

Typical appllcatlons of universal joints include aircraft, appliances, control mechanisms, electronIcs, Instrumentation, medical and optical devices, ordnance, radio, sewing machines, textile machInery and tool drives.

Universal joints are available in steel or in thermoplastic body members. Unlversal joints made of steel have maximum load-carrying capacity for a given size. Universal joints with thermoplastic body members are used in light industrial applications in which their self-lubricating feature, light weight, negligible backlash, corrosion resistance and capability for high-speed operation are significant advantages.

Universal joints of special construction, such as ball-jointed universals are also available. These are used for high-speed operation and for carrying large torques. They are available both in miniature and standard sizes.