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PULLEYS (Types of pulleys: (Fixed pulleys (A fixed pulley is a wheel that…
PULLEYS
Types of pulleys:
Fixed pulleys
A fixed pulley is a wheel that has a groove for a rope, chain or belt to go round it. It rotates around an axle that is fixed to an immobile surface. This reduces the load, R when effort, F, is applied
A fixed pulley is balanced when the effort, F is equal to the load, R: F=R
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Compound pulleys
This is a set of fixed and moveable pulleys, often called a block and tackle. If we use more pulleys it becomes more complex, but less effort is needed to move the load.
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Pulleys with belts
These are two pulleys or wheels that are certain distance apart. Their axles are parallel and they rotate simultaneously because of the belt. The rotation of one axle is transmited to the other via the connected pulleys. The two pulleys (and the two axles) rotate in the same direction.
The ratio between the rotation velocities of the pulleys, the gear ratio, is the same as in friction drives
Pulley trains with belts
This is a system of pulleys (or wheels) with a belt. There are two or more pulleys. The rotary motion of axle 1 is transmitted to axle 2 via the stretched belt that connects them. Pulleys 2 and 3, attached to the same axle, rotate at the same velocity. The motion of pulley 3 is transmitted to pulley 4 via the belt that
connects them. All the pulleys rotate in the same direction.
The gear ratio between the drive pulley (1) and the driven pulley (4) depends on the relative size of the pulleys in the system. It's expressed as a function of their diameters: (N4/N1)=(D1·D3)/(D2·D4)
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N1 is the velocity of the drive pulley N4 is the velocity of the driven pulley. D1, D2, D3 and D4 are the diameters of the pulleys to calculate the gear ratio: multiply the diameters of the even-numbered (driven) pulleys. Multiply the diameters of the odd-numbered (drive) pulleys. Divide the result of B by the result of A.
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