What is the function of a universal joint?

[SanStella]

Universal joint, also known as universal coupling, is a mechanical component that enables variable-angle power transmission. It is used in positions where the direction of the drive shaft needs to be changed and serves as the "joint" component in the universal drive system of an automobile. Non-constant velocity universal joint: When the angle between the two shafts connected by the universal joint is greater than zero, the motion is transmitted between the output shaft and the input shaft with a varying instantaneous angular velocity ratio, but the average angular velocity remains equal. Quasi-constant velocity universal joint: Refers to transmitting motion with equal instantaneous angular velocity at the designed angle, while transmitting motion with approximately equal instantaneous angular velocity at other angles. Constant velocity universal joint: The output shaft and input shaft connected by the universal joint transmit motion with always equal instantaneous angular velocity.