Re: [MV] winches, pulleys, leverage???????

James V (jim@valesh.com)
Thu, 16 Sep 1999 09:13:42 -0700 (PDT)

On Wed, 15 Sep 1999 CaptainGG@aol.com wrote:

> Mechanical advantage is gained whenever two pulleys are moving toward each
> other. Otherwise, there is just a change of direction of the cable or rope.
> The example you give of your winch run through a pulley on a tree, then back
> to the truck, gives a 2 to 1 mechanical advantage. If you went winch,
> pulley, pulley, tree, as in your second example, you would have a 3 to 1
> mechanical advantage. I would need to ask others on the list with more
> expertise about how that would effect the rated capacity of the cable and
> winch, but I believe you may exceed the safety margin.

Neither the cable
nor the winch 'sees' any greater load. In the 2X example, there are two
cables supporting the load, in the 3X, there are three. In both cases the
tension (and load) on the cable is devided, not multiplied by the number
of cables. i.e. to pull 100 pounds with one cable puts 100 pounds load on
the cable and winch. with one pully, that cable load is halved to 50
pounds. With two, 33.333... pounds, etc. The winch of course only sees
the load on its cable, not the force applied to the load.

> > Hope this is helpful > > Gerry Gardner > 1957 REO M35 (with winch)
>
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