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Re: [TowerTalk] rotor suggestions

To: <>, "'Tower'" <>
Subject: Re: [TowerTalk] rotor suggestions
From: "W2RU - Bud Hippisley" <>
Date: Mon, 28 Apr 2008 00:41:02 -0400
List-post: <">>
Dick (& others):

See my opinions / experiences interspersed below.

-----Original Message-----
From: Dick Green WC1M
Subject: rotor suggestions

>...I'm evaluating [rotor] options here. 

>Right now, I'm using a Tailtwister to turn a Cushcraft 40-2CD...The mast is
feet long, 2" diameter, 1/4" wall aluminum. 

>Here's the issue: I will soon replace the 40-2CD with a Cal-AV 2D-40A
16 sq ft windload, 34' turning radius, 163 lbs, K-factor = 5,542.)
Obviously, this is much more antenna that anything I've turned with the
Tailtwister, and it exceeds the K-factor rating by a substantial amount.

>Any opinions on the strategy?

Years ago, before the T2X was on the market, I had a full-size Wilson
interlaced 3-element 20 + 2-element 40 about six inches above my Rohn TB-3
thrust bearing, which was 2 feet above my Ham-M rotor.  My mast was
aluminum, and it was at least as thick-walled as that in use by WC1M.

At first my mast wasn't pinned, but I couldn't keep this duo-bander beast
from rotating in a mild breeze.  No matter how much I tightened down the CDE
clamp, the mast would chew its way past the serrations in the clamp.  So I
pinned the mast to the Ham-M top casting with a plated steel bolt.  The next
thing I knew, I *still* couldn't keep the beam from rotating in a mild
breeze.  Seems the breeze had used the steel bolt pin to chew a slot,
extending about 45 degrees around the circumference by the time I discovered
it, in the aluminum mast.

Lesson #1:  Steel makes a better mast than aluminum for large torques....

So I replaced the mast with a galvanized steel one.  This had the effect of
moving the "weak link" in the system down about two feet, and the next time
I saw the beam wandering in a mild breeze I went up the tower and discovered
that my mast clamp U-bolts had become J-bolts!  The ARRL DX Test was only
about two weeks away, however, so I replaced the bolts and hoped for the
best.  'Twas not to be.  The final catastrophe that befell me -- less than a
week before the contest -- was that the top casting of the Ham-M broke in
two in a "spanking" breeze.  I went through that winter's ARRL DX test with
the beams tied off toward Europe with ropes tied to the two ends of the
3-inch boom.

Lesson #2:  Don't use anything with a fixed brake wedge for large, large

>If anyone feels that the Tailtwister is sure to fail under the new load,
then I'd like to hear suggestions for a replacement. The two choices that
appeal to me are the Yaesu G-2800DXA or the M2 RC2800PX/AZ with the K7LXC
clamp....I prefer a rotor that can be purchased without the controller
because I plan
to use a Green Heron (by far, the best controller on the market.)

I have a Green Heron RT-20 running my primary T2X.  In fact, the firmware in
my RT-20 was the first to include (at my request) a T2X mode (that precedes
actual rotation with a momentary "pre-rotation" in the opposite direction to
free up the brake wedge, since mine jams more consistently than many other
T2Xs, I guess).  That refinement has worked fine, but this winter I have
developed a new problem.  It seems *my* T2X indicator pot is "scratchier"
than most during rotation, and it goes "open-circuit" long enough to
prematurely halt perhaps 30% or more of the rotations I undertake.  And of
course even new T2X brake wedges have a best-case resolution of 6 degrees,
so the inherent closed-loop precision of the RT-20 is rather wasted on the

Lesson #3:  My (admittedly ancient) T2X is not deserving of a controller as
nice as the Green Heron product.  If you're going to spend the bucks on a
nice PC-driven controller so you don't have to keep either your eyes or your
hands on the control box while you're in a contest, put something up the
tower that actually lets you do that.

So if all that is true, why am I still using a T2X?

Lesson #4:  If $$$ are an issue, it's sure hard to beat a T2X for basic
rotation of moderately big beams.

Dick, one final comment.  I wouldn't use a T2X for the antenna size you're
talking about for the following reason alone:  With a large antenna, on a
windy day the T2X can lose control during rotation.  I've had situations,
even with my relatively small "shorty-40" and CC 4-element 20, when powered
rotation would come to a halt during periods of sustained winds of 50+ mph
(not unusual during February storms here).  (Probably exacerbated by tired,
old motor start capacitors and long control lines to the top of the tower.)
And when you quit sending a "Rotate" command to the rotor, your big antenna
can actually speed up in response to the wind; I've had occasions when I've
chosen to manually turn off the AC power on the front panel of the T2X
control box to force the brake wedge to drop into position sooner than it
would under control of my normal 5-second delay -- so that the antennas
wouldn't get time before the wedge dropped into place to accelerate from the
force of the wind.    

Bud, W2RU 


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