the principle and advantages of Belt drives

A belt is a looped strip of flexible material, used to mechanically link two or more rotating shafts. They may be used as a source of motion, to efficiently transmit power, or to track relative movement. Belts are looped over pulleys(WeiKu). In a two pulley system, the belt can either drive the pulleys in the same direction, or the belt may be crossed, so that the direction of the shafts is opposite. As a source of motion, a conveyor belt is one application where the belt is adapted to continually carry a load between two points.
Belt drives have many advantages. They are simple and economical. They are very economical when shafts are separated by large distances. They require only low maintenance. Their lubrication is free. Parallel shafts are not required. They are highly efficient. Some misalignment is tolerable. And the variable speeds may be economically obtained by step or tapered pulleys.