Standard Pulleys
Pulleys are the complete opposite of gears in nearly every respect,
apart from the fact that they are used to transfer power across
a distance. There are four main types of pulleys, you can see
them below:
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The pulley is more frequently
used as a half bushing, but in this case it can be used as
a pulley. It has a relative size of 2. |
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The friction gear has a special
flexible plastic section inside it to allow for better grip.
It's relative size is 3. |
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This is the medium
sized pulley, and has six holes to allow peg connections.
It's relative size is 7. |
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Finally, the large pulley
has a relative size of 11. It is often used as a large steering
wheel. |
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In much the same way that gears can reduce and increase
power, so can pulleys.
In this model, by turning the handle of the larger pulley,
you can see that the smaller pulley moves around 3.5 times
quicker. This figure is not exact, however, as you must
always allow for slippage.
|
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This example
works the other way, with the friction pulley turning about
1.5 times slower. |
There are three major differences between pulleys and gears.
• Pulleys keep the direction of the axle
rotation the same.
• Pulleys transfer power using a rubber band.
• Pulleys cannot be relied upon for exact
power ratios (due to slippage).
