A pulley drive system is very easy to make and it will work even if the various parts are not quite lined up. When these pulleys are connected by a belt, the motor has to turn 6 times to make the larger pulley turn just once. This is because the larger pulley is 6 times the diameter of the smaller one. We say that such a drive system has a speed reduction ratio of 6:1. This ratio allows the motor to turn quite rapidly but also gives high torque or turning power to the axle. To get even higher torque, we can increase the size of the larger pulley or decrease the size of the motor spindle pulley. However, this will also reduce the speed of the axle.

The simplest form of pulley drive is the fixed pulley (Fig.1), where the force Z needed to raise the load Q is equal to the latter. The illustration shown in Fig.2 the load is suspended from the pulley; the (upward) force needed to raise the pulley with the load suspended from it is now only half the magnitude of the load (assuming the pulley itself to be weightless).

The flexible connecting elements used in pulley drive systems are ropes, belts, wires, chains, etc., made of a variety of materials (rubber, leather, textile fabrics, metal, etc.) These elements can take only tensile loading. Power transmission is effected through the action of friction between the flexible elements and the pulleys around which they pass. In some cases, however, a positive drive is obtained by means of chains whose links engage with the teeth on special toothed wheels called sprockets e.g.: bicycle or motorcycle chain drive.

Transmission of rotational motion between shafts at any distance apart can be effected through a belt drive. The necessary contact pressure between the belt and the pulleys is ensured by appropriate tightening of the belt. This may be achieved by means of a tensioning roller or pulley. By the use of a belt of V-shaped cross section (V-belt) the contact pressure can be increased and the power transmission thus made more efficient. In the pulley drive illustrated in Fig.3 each pulley consists of two halves which can be moved farther apart or closer together. The effective radius of the pulleys and therefore the transmission ratio can be varied at will.

Fig.4 illustrates a pulley drive that provides a simple solution of the problem shifting the position of the driven shaft in relation to that of the driving shaft while the shafts are rotating.

In Fig.5 a pulley drive system is used for producing symmetrical motion of two parts in relation to each other, e.g., for opening and closing of curtains, sliding of doors, etc.

Fig.6 shows a pulley drive utilized in a high-lift truck. When the driving shaft is rotated clockwise, the large pulley winds up the rope, thus shortening it, so that the platforms are raised. They are lowered by counterclockwise rotation of the shaft. The raising and lowering of a fire ladder is based on the same principle (Fig.7).