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## [Towertalk] Statics 101

 To: [Towertalk] Statics 101 k1ttt@arrl.net (David Robbins) Fri, 12 Jul 2002 10:17:19 -0000
 ```ARGH! How many times do we have to go through this. When you have a 2:1 advantage the ground crew only pulls down on the pole with 1/2 the weight of the load so the load on the gin pole is reduced by 1/2 the weight of the load. It is obvious from the vectors. Try this out for size. Go up the pole with a rope, over the pulley, down to the load, through another pulley, and back up to the top of the pole and tie it off. Now lift 100# and hold it. Each rope section now has 50# of tension in it. 2 lengths of rope from the top of the pole go to the load offsetting its 100# weight, one length of rope goes down to the ground crew which has to hold the 50# tension. Since all 3 are held up by the pole the pole supports 3*50# or only 150#, not the 200# it would have to hold without the extra pulley. David Robbins K1TTT e-mail: mailto:k1ttt@arrl.net web: http://www.k1ttt.net AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net > -----Original Message----- > From: towertalk-admin@contesting.com [mailto:towertalk- > admin@contesting.com] On Behalf Of Wendell Wyly W5FL > Sent: Friday, July 12, 2002 00:12 > To: Chris BONDE; jljarvis > Cc: towertalk@contesting.com > Subject: [Towertalk] Statics 101 > > Statics 101: An object is at rest when the forces up equal the forces > down. > > Don't matter how many pulleys you use, unless you make a second attachment > to the tower you don't gain anything as the ground crew holds the rope > (same > as tieing it to a ground) and the gin pole takes out twice the load since > there are two equal downward force vectors. If the forces were not equal, > the load would be going up or down really fast. The reason it looks good, > is that you must tie both the rope to the second pulley and the ground > crew > to ground in which case the ground crew only has to pull half as hard (but > twice as far), but the gin pole gets no relief and you have to re-rig the > whole thing when the load is only half ways up, which is quite > impossible!!! > > This is one of those things that you will only try once if you don't think > about it or not at all if you do. > > -----Original Message----- > From: towertalk-admin@contesting.com > [mailto:towertalk-admin@contesting.com]On Behalf Of Chris BONDE > Sent: Thursday, July 11, 2002 5:20 PM > To: jljarvis > Cc: towertalk@contesting.com > Subject: Re: [Towertalk] mast disaster avoidance > > > It has been awhile since I have done any mechanical stuff with pulleys. I > think that you are on the right road but not all the way. > > If you are lifting a 100lb weight with one pulley at the top, you need > 100+ > lbs on the other side to lift it. I would then say that there is 200+lbs > of weight on the pulley. > > If you are lifting a 100lb weight with 2 pulleys at the top and one on the > load, then you have a mechanical advantage and need only 1/3 of 100+ lbs > to > lift the weight (I think that that is correct, but it is a lot > less) Therefore, the total weight on the pulley is 100lbs plus the > reduced > amount hence less. > > I think that this is correct. > > Chris opr VE7HCB > > At 02:00 PM 2002-07-11 -0400, jljarvis wrote: > > >Mike... > > > >If you had a ginpole with a 2 wheel block on top (never seen > >one, myself. Do they exist?), you would reduce the load on each > >run of line, proportional to the number of lines. > > > >But the load on the axle is still the sum of the line-loads. > >i.e., unchanged. > > > >The compressive load on the ginpole itself is thus still the > >same, and the out-of-column bending loads are the same. > > > > > >Jim/N2EA > > > > > >-0- > >From: "Mike Gilmer" To: > >Date: Thu, 11 Jul 2002 12:16:03 -0300 > >Subject: [Towertalk] Re: mast disaster avoidance > > > >I agree with most of N2EA's post except: > > > > > Solutions using added pulleys still leave the same load on > > > the ginpole material itself > > > >This is not true. As has been oft-discussed on this reflector in the > >past (and still misunderstood), judicious use of "added pulleys" can > >reduce the total load on the ginpole. > > > >Mike N2MG > > > > > > > > > >_______________________________________________ > >Self Supporting Towers, Wireless Weather Stations, see web site: > >http://www.mscomputer.com > >Call 888-333-9041 to place your order, mention you saw this ad and take > an > >additional 5 percent off > >any weather station price. > >_______________________________________________ > >Towertalk mailing list > >Towertalk@contesting.com > >http://lists.contesting.com/mailman/listinfo/towertalk > > > _______________________________________________ > Self Supporting Towers, Wireless Weather Stations, see web site: > http://www.mscomputer.com > Call 888-333-9041 to place your order, mention you saw this ad and take an > additional 5 percent off > any weather station price. > _______________________________________________ > Towertalk mailing list > Towertalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk > > > > _______________________________________________ > Self Supporting Towers, Wireless Weather Stations, see web site: > http://www.mscomputer.com > Call 888-333-9041 to place your order, mention you saw this ad and take an > additional 5 percent off > any weather station price. > _______________________________________________ > Towertalk mailing list > Towertalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [Towertalk] mast disaster avoidance, jljarvis [Towertalk] FK4564 Rohn Gin Pole, Wendell Wyly W5FL [Towertalk] FK4564 Rohn Gin Pole, Jim White [Towertalk] mast disaster avoidance, jljarvis [Towertalk] mast disaster avoidance, Chris BONDE [Towertalk] mast disaster avoidance, jljarvis [Towertalk] mast disaster avoidance, Jim White [Towertalk] Statics 101, Wendell Wyly W5FL [Towertalk] Statics 101, Tom Rauch [Towertalk] Statics 101, David Robbins <= [Towertalk] mast disaster avoidance, EUGENE SMAR