N4KG comments / questions inserted below.
On Wed, 13 Jun 2001 11:37:14 -0400 "Guy Olinger, K2AV"
> 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.
How is this 2:1 mechanical advantage achieved?
Scenario 1 - End of rope is attached to the frame
of the top pulley. Rope runs down to Second pulley
with hook at load. Rope then runs up and through
the TOP pulley. Force in each vertical run of the
rope is 150 lbs. 450 lbs on top hook as proposed.
This is NOT how a gin pole is configured.
In a block and tackle, one end of the pull rope
is attached to one of the pulleys. The LOAD is
attached to one of the end hooks. Multiple
pulleys can be mounted co-axially.
A block and tackle can be used to pull the rope
through the gin pole (two ropes required) but
the Gin Pole Pulley CANNOT be configured to
be part of a block and tackle. de N4KG
> 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...
> > From: David Robbins <firstname.lastname@example.org>
> > Date: 2001/06/13 Wed PM 02:21:59 EDT
> > To: K7LXC@aol.com, reflector -tower <email@example.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
> > 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,
> > > firstname.lastname@example.org 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://email@example.com
> > web: http://www.k1ttt.net
> > AR-Cluster node: 145.69MHz or telnet://k1ttt.net
> > List Sponsor: Are you thinking about installing a tower this
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> > -----
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> 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
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> Submissions: firstname.lastname@example.org
> Administrative requests: towertalk-REQUEST@contesting.com
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