This is a hash of my high school physics teacher's illustration on pulley
mechanics. Stuck with me ever since. Something about a picture worth a 1000
words.
Lightweight Larry weighs 100 pounds. Normal Nelson weighs 150. Heavy Henry
weighs 300 pounds. The tower section weighs 300 pounds.
Straight pulley: Heavy Henry on one side holding steady, section on the other.
600 pounds on the top hook.
2:1 advantage: Normal Nelson on one side holding steady, section on the other.
450 pounds on the top hook.
3:1 advantage: Lightweight Larry on one side holding steady, section on the
other. 400 pounds on the top hook.
Fun part was class asked to calculate acceleration of Lightweight Larry on the
straight pulley...
73
>
> From: David Robbins <k1ttt@berkshire.net>
To: <towertalk@contesting.com>
> Date: 2001/06/13 Wed PM 02:21:59 EDT
> To: K7LXC@aol.com, reflector -tower <towertalk@contesting.com>
> Subject: Re: [TowerTalk] Ginpole for 20 foot sections
>
> of course the lifting rope load remains the same, but the force required on
> the
> pulling end decreases so the total load on the gin pole does get reduced.
>
> for example, with a standard gin pole lifting 300lbs at the top of the pole
> you
> have a 300lb load plus 300lb of pull from the other side giving you a worst
> case
> 600lb force on the gin pole (static load, some more is required to get things
> moving, overcome friction, etc).
>
> with a 3:1 advantage pulley system you still have the 300lb load on one side,
> but the rope pulling down on the other side is only adding 100lbs of force to
> the pole, so the total is now 400lb. which of course is a 1/3 reduction from
> the 600lb you started with.... note the 3:1 and the 1/3 reduction is just how
> it
> works out. with a 2:1 advantage you only reduce the total load from 600 to
> 450lbs of a reduction of only 1/4 of the load... and taken to extreme, with an
> infinite mechanical advantage you still have 300lbs of load so you only reduce
> the total load on the pole by 1/2, the lowest you can get.
>
> another advantage of a pulley system like that is you can use a lighter weight
> rope since each pass of it between the pulleys divides the load up. so for a
> 3:1 system with a 300lb load you only need a rope that can handle 100lb of
> tension instead of 300lb... but of course you have to pull 3x more of it to
> lift
> the same distance.
>
> K7LXC@aol.com wrote:
> >
> > In a message dated 6/12/01 11:45:50 PM Pacific Daylight Time,
> > w7ni@easystreet.com writes:
> >
> > > A 3:1 mechanical advantage block and tackle system does, indeed, relieve
> > > about 1/3 of the load on the gin pole, in addition to reducing the number
> > of
> > > bodies required on the pull rope.
> >
> > You sure? Isn't a hundred-pound load going to weigh 100 pounds no matter
> > how the block and tackle are set up? The load effort on the end of the rope
> > will be reduced but the dead weight of the load stays the same. You still
> > need a suitable ginpole.
> >
>
> --
> David Robbins K1TTT
> e-mail: mailto://k1ttt@berkshire.net
> web: http://www.k1ttt.net
> AR-Cluster node: 145.69MHz or telnet://k1ttt.net
>
> List Sponsor: Are you thinking about installing a tower this summer? Call us
> for information on our fabulous Trylon Titan self-supporting towers - up to
> 96-feet for less than $2000! at 888-833-3104 <A
> HREF="http://www.ChampionRadio.com";>
> www.ChampionRadio.com</A>
>
> -----
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
>
>
List Sponsor: Are you thinking about installing a tower this summer? Call us
for information on our fabulous Trylon Titan self-supporting towers - up to
96-feet for less than $2000! at 888-833-3104 <A
HREF="http://www.ChampionRadio.com";>
www.ChampionRadio.com</A>
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|