The belt drives are machine elements that are classed as traction mechanisms in the field of transmission or conversion elements. They transfer torque and speed between guiding members such as wheels or pulleys. The motion is transferred by traction mechanisms that can only absorb tensile forces. Toothed belts and chains deliver positive transmission of movements.
Traction mechanisms such as cables, flat belts and V-belts, on the contrary, allow for non-positive transmission. In non-positive belt drives, the circumferential force between the belt and the pulley is transmitted according to the principle of cable friction.