Hamad:
I highly admire the skill and craftsmanship, of any one individual who can
design and build a self supporting crank up tower at a cost and quality
comparable to towers available today to the radio amateur. A daunting task,
in my opinion. I appreciate your burden of cost and shipping costs of
commercially made towers to your location, indeed, you have difficult
circumstances.
After closely examining an old Tri-Ex Tower during a refurbishing project,
I've gained an appreciation for how much design thought and precision is
necessary in fabrication of a 3 section crank-up. Also I learned how there
is more than one way to route lifting cable(s).
The shape of the tower lattice structures, at the tops of sections A and B,
are not flat trangular in cross section, iin order to properly locate the
pulley and route the lifting cables. In fact, take a look at the last page
of a TriEX tower manual from the web for some examples of pulley mounts:
http://www.hy-gain.com/man/pdf/HG-70HD.pdf
The careful placement of the pulleys and cable routing is not apparent at a
casual glance. Close inspection, as, when you plan a cable replacement,
reveals quite close tolerance hardware, (clevis pins, precision rollers) due
to the the tight clearances between moving tower sections. For example, it
is not possible to use cable clamps to terminate lift cables due to tight
routing clearances of the cable. (And because the manufacturer does not use
them in his original design --Hi Steve (:->) )
I was told that binding pulleys wear and chafe the cable, and is a cause of
tower lift cable failures.
Go to Google and do a Boolean Search, using the terms: crank up tower
+bind to find a lot of tower talk archives, and other useful informaton
about pulleys, and other mechanical issues for crankups.
See:
http://lists.contesting.com/archives/html/Towertalk/2002-03/msg00040.html
for a good piece by Steve, K7LXC. and another at:
http://lists.contesting.com/archives/html/Towertalk/2001-11/msg00244.html
This old Tri-Ex HZN 354 tower I am working on, part of an old tower
trailer, has precision rollers, maybe 1" dia at each corner that closely
fit and roll with the corner tube of the next larger section, making the
movement smooth and reliable. I was told that when this precision fit is
especially needed is when high winds demand a wise decision to lower the
tower. Problem is, this may become difficult or impossible, at a critical
time, due to wind caused side stresses causing a non-rollered tower sections
to bind, and not descend on demand. The manual cited above devotes quite a
bit of writing with many cautions, to dealing with and fixing binding
sections of their tower. A well known manufacturer told me that rollers
distinguish a 'professional' tower from most amateur towers..
With respect to lift cables, I discovered there are TWO cables used in this
tower to lift the two movable sections vertically. One cable goes from the
base section-mounted winch, up over a pulley mounted on the top of the base
(A) section, then down, terminated and anchored at the base of the middle
section (B). Hmmmm... The SECOND lift cable is anchored TO THE BOTTOM OF
THE BASE (A) section, routed upward, inside of section B, goes to the top of
B over a pulley, to the bottom of section C, the top section. This design
must do something better than a single cable, but I don't know what. It
might be, that this insures more even, simultaneous, proportional,
telescoping movement of the two movable tower sections. Or, I notice that
a single cable design would have the cable routed in an extreme, full S
shape at each movable section, forcing the cable to do two quick, opposite
flexing, 180 deg turns at each section, perhaps causing a shorter cable
life and adding frictional losses.
This tower is probably 35-40 years old, and apparently, the galvanizing was
done exceedingly well, there is not a spot of rust on the tower itself, but
a lot of rust in various areas of the trailer carrying it, (as you can see
from the pictures...)
Sooo Hamad, my hat is truly off to you, I wish you success in building a
quality crank-up tower from scratch....a huge accomplishment for an
individual. I can take and post to the web detailed pictures of the pulley
mounts on the tower, if it would be helpful to you, in designing
yours...Give me a little time to post these... also check out current
pictures at:
http://groups.msn.com/towertrailers/shoebox.msnw?action=ShowPhoto&PhotoID=1
http://groups.msn.com/towertrailers/shoebox.msnw?action=ShowPhoto&PhotoID=7
http://groups.msn.com/towertrailers/shoebox.msnw?action=ShowPhoto&PhotoID=8
73, DX, de Pat Barthelow AA6EG aa6eg@hotmail.com
From: "Jim Lux" <jimlux@earthlink.net>
To: "Hamad Mannai" <a71aw@mail.com>, <towertalk@contesting.com>
Subject: Re: [TowerTalk] Trying to build my own crank-up tower
Date: Thu, 24 Feb 2005 20:24:54 -0800
----- Original Message -----
From: "Hamad Mannai" <a71aw@mail.com>
To: <towertalk@contesting.com>
Sent: Thursday, February 24, 2005 12:38 PM
Subject: [TowerTalk] Trying to build my own crank-up tower
Hello All,
I am trying to build my own 50 ft crank up tower (using 3 sections of 20
ft. each, 5 ft overlaping for the 2nd and 3rd sections). I did all the
drawings, measurements and weights which ables this tower to be free
standing. Now I am stuck with 2 major issues tobe sorted out :
1- Do I have to use any sort of (sleeve bearings) to avoid friction
between the sections while cranking up or down? or can I just make the
sections as tight as possible to each other to avoid free movements?
Not too tight, or it will bind and get stuck.
2- Whats the best way to distribute pullies through the sections to manage
the up and down mechanism?
It's sort of hard to describe in words. Say your sections are A, B, and C,
from bottom to top. The cable goes up section A to the top, where there's a
pulley, then down to the bottom of section B, where there's a pulley, then
up to the top of section B, where there's a pulley, then down to the bottom
of section C, where it attaches.
Fire truck extension ladders work the same way.
I know I am asking too much, but I never saw a crank up lattice tower
closely. And I have to build it myself because its not availabe here and in
case of importing it from US/Europe, it will cost me $2000+ as shipping
charges only!!
I would think that drawings are available of some standard towers which you
could look at to get ideas.
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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