[aprssig] APRS Irrigation Pipe 55' mast

[Robert Bruninga]

>There are folks with extendable (nested) poles who 
>use them for a sort of aerial photography instead of
> lifting antennas into the sky.   See: 
>
> http://www.bird-shots.com/xaping/pap/pole_animation.htm 

Neat page!   But that is a good example of how *NOT* to 
engineer it for leight weight and structural efficiency.

Lets say the overall load is 60 Lbs.  Raising it 50' takes
3000 ft-lbs.  But the way shown in the animation has to 
deliver that in just 6 feet of pulling (7 moving sections). 
That takes 500 lbs of force on the cable and the first 
pulley!  THink of it as raising all sections in parallel!

The far less stressful way on you and all components 
is to have pulleys on the top and bottom of each moving 
section as I did in my design and you still have to lift the 
same 3000 ft-lbs but if it is an 8 section mast, then you
have 13 up/dn runs of 6 feet of rope and so these add
in series.  Now, this 78 feet of rope does the same work,
in raising the 3000 ft-lbs, but you only have to pull on it
with a force of 38 lbs, not 500.

This is much easier to pull by hand.  Yes, you can 
find a 500 lb winch to do the job, but it takes pulleys,
structure, and rope that are 13 times stronger than 
needed.

The advantage of the parallel method is less fussing
with pulleys and less rope to wind up.  Put the series
method I use allows the pulleys, structure, and rope 
to be 13  times smaller (in this 7 section example) 
and usually worth it.

In my 3 section mast (2 move) to 50 feet, the 
mechanical advantage of my method is only 3 to 1.  
But that is my preference when raising it by hand.

http://www.ew.usna.edu/~bruninga/Antenna-Ipipe.html

But either way will work...

de Wb4APR, Bob

----- Original Message ----- 
From: "Robert Bruninga"
Subject: Re: [aprssig] APRS Irrigation Pipe 55' mast