NOW you tell us that you (W7NI) used a block and tackle
"IN PLACE OF" the single pulley at the top of the gin pole.
I *assume* that the block and tackle was installed between
the top of the gin pole and the LOAD which is consistent
with your measurements. The early arguments were not
clear on the placement of the mechanical advantage. A
block and tackle installed between the puller and the end
of a rope going over a SINGLE pulley at the top of a gin pole
will provide a mechanical advantage for the puller but NOT
for the gin pole, as I argued from the start.
It would have saved a lot of arguing to have made that clear
from the start. We've been arguing Apples and Oranges
with blindfolds on all this time :-)
SO, yes, I agree that a Block and Tackle installed between
the top of a Gin Pole and the LOAD *will* reduce the load
on the gin pole compared to a single pulley at the top.
The problem is simple once we have a clear description.
Tom N4KG
On Wed, 13 Jun 2001 Stan or Patricia Griffiths <w7ni@easystreet.com>
writes:
> I thought I had sent this message to the reflector but apparently not
> . . .
>
> Stan or Patricia Griffiths wrote:
>
> > Yes, I am ABSOLUTELY sure. Like I said, I set up a demonstration
> to prove it,
> > showed it at a Willamette Valley DX Club meeting with the help of
> W7RR and
> > convinced each and everyone present that it works exactly as
> described.
> >
> > What I did was set up a 6 foot vertical mast made of 1 inch
> diameter aluminum
> > tubing. Next, I rigged it with a small single pully at the top
> and with a
> > spring scales inserted between the pully and the top of the mast
> showing the
> > downward force on the pully which is the same as the load on the
> mast. Next, I
> > installed a known weight of 15 pounds (measured by the same spring
> scale earlier
> > in the demonstration) on the load rope. Next, I took up slack on
> the "pull"
> > rope and when the weight lifted off the floor, W7RR read the
> scale. It said 30
> > pounds. Why 30 pounds and not 15 pounds? Because there are TWO
> ropes pulling
> > down on the pully, one attached to the load and the other one
> attached to the
> > hands of the person raising the load. Both of these ropes
> (technically, it is
> > only one rope but it has the same effect as if it were two
> separate ropes, each
> > attached to the pully, in terms of applying load to the pully and
> mast) have 15
> > pounds of tension each and pulling in the same direction (down)
> and all of that
> > load (15 pounds EACH) is supported by the mast and pully.
> >
> > What I did then was make a small block and tackle with a 3:1
> advantage and put
> > it in place of the single pully. I again raised the load off the
> floor and W7RR
> > read the scale in series with the pully. I now read 20 pounds
> instead of 30
> > pounds or 2/3 of the first number. Now there are 3 strands of
> rope holding the
> > weight (15 pounds) so the tension in the rope is 5 pounds instead
> of 15 pounds
> > and the tension in the pull rope is also 5 pounds, since it is the
> same
> > continuous rope. So now there is effectively FOUR ropes pulling
> down on the
> > pully (and mast) but each one only has a tension of 5 pounds each
> (total 20
> > pounds) instead of TWO ropes with a tension of 15 pounds each
> (total 30 pounds).
> >
> > This REALLY works. If you STILL don't believe it, you can always
> rig this at
> > home and TRY it yourself. It is not rocket science. Also, it is
> not
> > intuitively obvious that it works which is why there are so many
> non-believers.
> > You certainly can't deny that it is a VERY IMPORTANT concept and
> reducing the
> > load on the gin pole by 33% could save your neck when you are
> lifting that 250
> > pound long steel mast . . . isn't it worth checking it out?
> >
> > I have actually thought about making my demo kit available as a
> traveling
> > program but there is nothing in it you can't get at the local
> hardware store for
> > a couple of bucks.
> >
> > You know, when we hashed this out last time here on towertalk, I
> went away with
> > the ugly feeling there were still a lot of non-believers out there
> and I had
> > failed miserably to get this VERY IMPORTANT point across. I hope
> I made it this
> > time. The bottom line is that you can try it yourself . . . so I
> don't want to
> > hear from any nonbelievers who have not actually rigged this up
> and made the
> > measurements themselves . . . this means I should not get ANY
> nonbeliever email
> > on this since, as soon as you try it, you will become a believer .
> . . becauses
> > it is absolutely TRUE.
> >
> > Stan
> > w7ni@easystreet.com
> >
> > 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.
> > >
> > > Cheers, Steve K7LXC
> > > Tower Tech
>
>
>
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