Another Mechanical Engineering Question re: free-stand antenna mast

Most of us are not "computer people" so post your technical questions and comments here. If you have computer or Internet expertise, share it here.

Moderators: carlson1, Keith B

Post Reply
User avatar

Topic author
Charles L. Cotton
Site Admin
Posts in topic: 1
Posts: 17787
Joined: Wed Dec 22, 2004 9:31 pm
Location: Friendswood, TX
Contact:

Another Mechanical Engineering Question re: free-stand antenna mast

#1

Post by Charles L. Cotton »

Quite some time back I asked a question about a trolley system for an antenna mast. I have another question about a free-standing antenna mast, but rather than mix apples and oranges, I'm starting this thread.

I'm putting up a repeater at a location other than my house and I want to use a free-standing mast going to about 70'. I like the telescoping mast KD6X designed and built here, but his goal was to have a fully retracted unit that he could easily move in and out of his yard. (He as concerned about his HOA.) I don't need that feature, but I do want to be able to drop the antenna down in bad weather to lessen the likelihood of a lightening strike.

Here's my question. I want to use three 24' joints of square aluminum (possibly steel) tubing in a telescoping pulley system similar to KD6X's five-section mast. I would prefer to use 3", 2 1/2" and 2" each 1/8" wall to limit the complexity of the unit. However, I don't know if there is an engineering taper ratio that must be maintained for the mast to be self-supporting (i.e. without guy wires). The mast will also have a tilt base, but that's not relevant to this issue. High lighting masts are a continuous taper from top to bottom and KD6X used five sections ranging from 3" to 1" for a mast that extends to 28'. Again, he did his that way to make it easier to move in and out of his garage, nevertheless he has five different sizes of aluminum for a 28' span where I'm proposed to have only three different sizes for a 70' span.

Okay mechanical engineers, please tell me I can do it will three joints with a one to two foot overlap!

Thanks,
Chas.
User avatar

Lynyrd
Senior Member
Posts in topic: 1
Posts: 1536
Joined: Wed Jan 06, 2016 10:20 am
Location: East Texas

Re: Another Mechanical Engineering Question re: free-stand antenna mast

#2

Post by Lynyrd »

I've never worked with aluminum on that scale, but I've worked a lot with steel tubing. You'd be surprised how limber a 24" joint is when the walls are that thin. If you went with steel you would definitely have to go to at leas 1/4" wall and then you would have about 700 lbs of weight to deal with. Friction is also going to be tough to overcome on a 22 foot slide. I noticed on your link they had some kind of polymer in between the joints. It is probably silicone based to reduce friction.
Do what you say you're gonna do.

WTR
Banned
Posts in topic: 1
Posts: 1931
Joined: Mon Nov 16, 2015 10:41 pm

Re: Another Mechanical Engineering Question re: free-stand antenna mast

#3

Post by WTR »

I would definitely use steel. You might take a look at how HVAC jacks are made. They don't go up 70' but they are made of square steel and are telescopeing. They have a crank similar to a boat winch to extend them. You might consider a small ATV winch like the ones sold at harbor Freight as a 70' leach will be heavy.
Post Reply

Return to “Technical Tips, Questions & Discussions (Computers & Internet)”