On 05/24/08 04:29 am Roger (K8RI) wrote:
> Is there a good description of the mechanics for a crank up mast on the
> web? I'm looking at three sections or more. I've found a couple of
> basic designs, but I haven't be satisfied with the safety aspect and
> they were basically just crank up poles. Standard pipe (schedule 40)
> might or might not be strong enough so some sections could be schedule
> 80. In addition to the raising cable(s) there need to be guides to
> prevent each section from rotating inside the next larger size. A
> single cable, although easy to route has to support the entire weight so
> it should have some sort of latching mechanism. (a single pulley in the
> base of each section with a single on the outside at the top of the
> section) It'd be even nicer if each section could be raised and lowered
> independently of the rest which of course would mean a winch mounted at
> the top of the previous section which would add overall weight and a
> larger wind profile. Ideally the entire mast would rotate. Also the
> *innards* need to be accessible if the cable breaks or hangs up.
> If all else fails I can build a "rotating", fold over mast of the
> desired height that would use the support for a raising fixture which
> would be much simpler and far less expensive, but I'd really like to go
> with the crank up. However, right now the rotating, fold-over looks to
> be much more practical and much faster to build at probably 1/3 to 1/4
> of the price for the rotating, crank-up.
> I have lots of ideas and could eventually build one to easily get 60
> feet, but I'd rather not go through all the design and experimentation
> stages if the information is available. That sort of experimenting is,
> or can be expensive. I tend to err on the conservative side so if I do
> the design it'll be far heavier than an existing design. As it is the
> price of steel is well over twice what I was paying just a couple years
> ago and the local supplier told me to expect another 40% to 80% by the
> end of summer I need to get busy. I used to use a lot of steel for
> building assembly jigs, tables, and other fixtures including masts and
> telescoping masts. Even the 60' fold over is going to be a bit pricey
> just for the material.
> This would replace the 25G which is replacing an old 40' Aluminum tower
> and will support the tri-bander that is now on top of the 45G which
> hopefully will make room so something on 40.
> At least that is the current thought.
From what I have read, you need tube rather than pipe; and
square-section tubing would eliminate the rotation problem.
But it seems to me that what you are trying to do is reinvent the US
Tower Corp.'s MA-series, or something like it.
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