PULLEY SYSTEMS  VELOCITY RATIO  3
V. Ryan © 2017
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In this example the driver pulley wheel is the largest of the two. Because it is the largest it will automatically be the slowest and output less rpm’s than the smaller driven pulley wheel. 

The diameter of the driver pulley wheel is 600mm and the driven pulley wheel is 200mm. This means for every single revolution of the larger driver pulley wheel, the smaller driven pulley wheel rotates three times. This due to velocity ratio. The ratio can be worked out mathematically in different ways. The two most likely methods are shown below. Please note, the driven pulley wheel is placed on top of the equation as it is the larger number. 

PLEASE NOTE  WHEN WORKING OUT VELOCITY RATIO  THE
NUMBERS ARE ARRANGED IN THE SAME ORDER OF THE PULLEYS  IN THIS EXAMPLE
THE DRIVER COMES FIRST, FOLLOWED BY THE DRIVEN IN AN EXAM YOU MAY BE ASKED TO PUT THE DRIVER OR DRIVEN NUMBER FIRST. 



An alternative method is to call the ‘DISTANCE MOVED’ as simply being DIAMETER. This makes the calculation easier to understand, although using this terminology may not be accepted in an examination.  
This means that the larger pulley wheel (the driver pulley wheel) revolves a third of the rpm compared to the smaller driven pulley wheel. In effect the driver pulley wheel is slower and revolves a third as many times as the driven. This means if the rpm of the driver pulley wheel is MULTIPLIED by 3, the output rpm of the driven pulley wheel will be found. 

