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[Towertalk] Ham M slippage?

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Subject: [Towertalk] Ham M slippage?
From: (Jim Maxwell)
Date: Wed, 01 Jan 2003 10:21:03 -0800
  You may be experiencing a different kind of slippage.  Let me
tell you a story of another kind of slippage that I'd never heard of
before I got the disease.  

I'm using a Yaesu G-2800 rotator with a Force-12 DXer Plus
(lots of elements on a 34' boom), with a smaller beam below
it.  They're supported by an old Tristao CZ-454 tower.  Both
are (supposed to be) wind balanced.  That, of course, may not
help in gusty conditions.  

The stacking pole is pinned through the rotator mounting clamps,
so the pole itself won't twist with respect to the rotator.

The rotator itself is attached to a triangular base plate that rests on
three horizontal cross pieces in the tower.  The plate  has three
strips welded to the bottom that are supposed to keep the plate
itself from turning.  Most tower installations are similar, I believe.

Well, I live in a high wind area, and over a period of time the torques
caused the entire assembly to twist: antennas, mast, rotator and
plate all together.  The mast couldn't turn in the rotator clamps
because of the pin.  The pin held as did the rotator.  The strips
on the bottom of the plate resisted turning, so what they did was
slowly bend the three horizontal struts on the tower until the tower,
at that level, looks pregnant.  Eventually it became so pregnant
that the mounting plate rotated inside the tower.  The hero of the
episode was the rotator.  

Even with those enormous turning moments, the rotator didn't
break, and in fact still works normally.

Thinking back, I had warning that something was going on, but I
didn't heed those warnings.

I suggest you climb the tower and take a close look at that rotator
mounting plate and the cross pieces it's resting on.  See if it's starting
to move.  If it is, fix it.  You may be able to check it out at first
without climbing the tower - take a pair of binoculars and see if the
cross pieces are starting to look pregnant.

73.  Jim, W6CF wrote:

>It is also possible that the MAST is slipping in the
>U-bolts of the Rotor, OR, the BOOM is slipping on
>the Mast.  I've had that problem when 'single' nuts
>worked loose on the U bolts.
>Tom  N4KG
>On Tue, 31 Dec 2002 20:13:01 -0500 GEORGE PRITCHARD <>
>>My tower mounted rotator swings a 4 element quad. In a wind storm 
>>last week, it was slipping during 45 mph gusts of wind. The next day 
>>it seemed "normal" and doesn't turn while the brake is on. Can this 
>>rotor slip with out damage, or is the bell housing worn? any 
>>experience with this? Thanks,  Is this how to post a thread on the 
>>George AB2KC 
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