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Re: [TowerTalk] Why a Prop Pitch?

To: "Richard (Rick) Karlquist" <>,<>, <>, <>
Subject: Re: [TowerTalk] Why a Prop Pitch?
From: Jim Lux <>
Date: Wed, 24 Jan 2007 13:25:25 -0800
List-post: <>
At 12:08 PM 1/24/2007, Richard \(Rick\) Karlquist wrote:
> >
> > Just as a question, since I have my Baldor catalog handy, what is the
> > inside diameter of one of the telescoping tubular towers?  (i.e. how
> > small does the motor have to be?).   It might well be that a standard
> > Jim, W6RMK
>Not tubular towers, rather lattice type crankups.  UST has
>those dimensions on its web site.  For the "5" series towers,
>the max diameter is 8.25 inches.

NEMA 56C is a 5 7/8" bolt circle, with the flange being a bit bigger 
in diameter than that. A typical 1/4 HP to  1/2 HP TENV DC motor is 
about 6.5" across the mounting foot.

Looking through the Boston Gear catalog, it looks like you can get up 
to about 100:1 reduction in a 600 series planetary set (triple 
reduction).. That might work (1750 nominal motor speed-> 17.5 RPM 
antenna mast speed, which is a bit fast, but you could run the motor 
slower than no load speed).  That's at 90VDC, so if you ran it at, 
say, 15 V, it would be more like 2 RPM, which is more 
plausible.However, it also violates the basic gear train design rule 
of "never use the highest or lowest ratio available".

There's probably other gearboxes available, though.

>Besides this constraint, you would like to be able to get
>the rotor in from the side.

So, is there an aperture that you sort of slide it in through, and 
tilt it, dropping it down against (or shoving it up against) a 
mounting plate?  Like between the diagonal cross brace and the vertical tubes?

>   You can't drop it in the top
>(at least on my HDX5106), and it would be a major hassle
>to bring it up from the bottom, because you would have to tilt
>the tower over, remove the positive pull down stuff,
>stuff the rotor in the bottom past the positive pull down
>mount, and then reinstall the pull down.
>It turns out that you can disassemble a prop pitch into
>3 pieces and get it in from the side, then put it back together

You could probably do the same with a standard gearhead and motor, 
but... it's a pain to have to reach in and tighten all those bolts, 
etc.  I suppose, too, you're still left with the "how do you couple 
the mast to the output shaft question.  The output shaft is typically 
a 3/4" or 1" diameter keyed shaft.  You can get a standard coupling 
from that to a 4 hole flange, which you could then bolt to some sort 
of mast clamp.  I'm sure someone makes that piece.  Most of the gear 
boxes in that 1/2 HP range can take a pretty hefty axial and/or 
radial load too.

Hmm.. something to occupy my spare time when I want to browse through 
the mechanical catalogs...

Seems that, in the long run, figuring out how to use standard 
industrial components might pay off.

>Another approach used is to cut out a tower brace and replace
>it with a removable one.  I would hate to butcher a tower like
>this, unless it was just a Rohn 45 section.
>Rick N6RK


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