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Pulley and belt Transmission


What is Pulley?

  • A Pulley is a wheel mounted on the shaft which can move a belt along it's circumference.
  • It can be used to lift loads and transmit the motion.

  • Pulleys are used to increase or decrease the speed of rotary motion.
  • There are various times of timing pulleys like Flat Pulley, V Pulley, Timing pulley, etc....
  • Below are useful calculations which are used in belt and pulley transmission.

  • In above image two pulleys are shown: Driver pulley is mounted on the shaft which is connected with motor or any other source and Driven pulley is which is driven by driver pulley.
  • In above example the diameter of mm and rotating at  100 revolutions per minute (rpm).
  • The driven pulley has a diameter of 120 mm.
  • If we want to calculate the rpm of the driven pulley there are two options:

Option-1:

      We can use the standard equation N1D1=N2D2
N1= rpm of driver pulley
D1= Diameter of the driver pulley
N2= rpm of driven pulley
D2= Diameter of the driven pulley
            Hence, N2 = (N1D1)/D2
                              = (100x40)/120
                              = 33.33 rpm 

Instead of flat pulley and belt if timing pulley and belt are used the equation will be N1T1=N2T2,
Where T1 and T2 indicates the number of teeth of driver and driven pulley and N1 and N2 indicates the rpm of driver and driven pulley.

Option-2:

Calculate the velocity ratio
Velocity ratio =  Diameter of  driven pulley / Diameter of driver pulley
Velocity ratio = 120/40 = 3
The output speed of a pulley system is calculated as follows.
Output speed =Input Speed / Velocity ratio
            output speed = 100 3 = 33.3 rpm.

By above options you can calculate unknown diameter of rpm if you have  factors.

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