Crane pulley group works as follows: n is odd when the rope driven pulley is started. With a moving pulley when there are three rope commitment, followed by the addition of a moving pulley to add two rope. Such as: n = 5, you need two moving pulley (3 +2). n is even, the rope from the fixed pulley for the beginning, then all the pulleys are only two rope to bear. Such as: n = 4, you need two moving pulley (2 +2); as required to determine the number of fixed pulley, the principle is: the general: two rope with a moving pulley, a moving pulley generally with a fixed pulley. Force direction does not require change, the even number of rope can be reduced by a fixed pulley; to change the direction of force, need to add a fixed pulley.
Through the above explanation, the working principle of the crane pulley group can be summarized as follows: singularity and stability; a certain action with a certain, even reduced by a certain change.
A simple machine that rotates around a central axis by a disc that is rotatable about a central axis and a cable (rope, tape, cable, chain, etc.) that transverses the disc. The pulley is a lever of a simple mechanical. In my country as early as the Warring States period of the book "Mo Jing" in the record on the pulley. The center shaft fixed fixed pulley called pulley, is the deformation of the arm lever, no effort but can change the direction of force. The center wheel moves with the weight of the pulley called the pulley, is the deformation of the arm lever, can save half of the force, but do not change the direction of force. In practice, a certain number of moving pulleys and fixed pulleys are often combined into various types of pulley blocks. The pulley group is both labor-saving and can change the direction of force. Commonly used in the factory differential pulley (commonly known as chain hoist) is also a pulley group. Pulley blocks in the cranes, hoists, lifts and other machinery are widely used. There are two pulleys: pulley and pulley, combined into a pulley group.