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Re: [TowerTalk] Add on 3" mast brake?

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Add on 3" mast brake?
From: Grant Saviers <grants2@pacbell.net>
Date: Mon, 14 Nov 2022 14:58:16 -0800
List-post: <mailto:towertalk@contesting.com>


> This post makes me wonder what rotator people with really large 80m Yagi's
> like W0AIH use?

Makes me wonder too, since all high power gear trains have backlash.

The small PP I had from K7NV showed a surprising amount of backlash, more than Kurt thought it should have. He also commented that the small unit has the highest total gear reduction and thus the most resistance to turning. I have a medium PP that needs rebuilt, but am not sure I want to get into it and where would I get parts?

Ken G., Mr JKantennas, told me the Orion2800 was up to the job on his 80m. Which caused me to fix up an older 2800 and put it in while waiting for Kurt to rebuild 2 small PP, which with his sad passing are in limbo. However, the 2800 broke off a gear tooth on the output shaft gear in a wind storm 2 weeks ago. It had a worn (badly rusted) spline and I tried to fix that with 4 set screws into the shaft female spline. That didn't work, they loosened an deformed and the gear tooth broke.

I've also learned to cross drill rotator mounting bolt heads and safety wire them. My tower guy said he finds a lot of loose/missing rotator mounting bolts from the shock, vibration, etc.

Talking to M2 today I ordered a new output shaft and splined mast clamp plate. I was told "first time for a broken tooth". The output shaft is hardened and the plate mating spline coupling is soft and takes the wear. Replacing both about was worth it re a new 2800 cost. A learning was if there is spline backlash, replace the top plate since it is the very short end of the gear/spline shaft + plate cost. Removing the motor is not recommended as the alignment is tricky.

Also, make sure the center bolt on the plate is well waterproofed to prevent water intrusion rusting the spline.

Thanks so far for brake suggestions.

Grant KZ1W

On 11/14/2022 11:35, john@kk9a.com wrote:
This post makes me wonder what rotator people with really large 80m Yagi's
like W0AIH use?

I believe that you want to brake the mast and not the rotator which is not
easy to add now. I am told that prop pitch motors originally had brakes but
I am not sure what happened to those mechanisms.  FWIW, I have a medium prop
pitch rotator on my Rohn 65 tower and it easily fits inside, perhaps a large
also fits.

GL
John KK9A



Grant Saviers KZ1W wrote:

My 80m 2L beam is destroying rotators (sm PP and Orion 2800). So far no
problems with the beam.

What is happening is any backlash in the gear train leads to rotational
oscillations from the turbulent high wind at my QTH plateau/ridge and
results breaking gear teeth off.  The 375# antenna and 100ft elements
provide the momentum/jerk at the stop of movement.

So am looking for designs of a secondary brake I can fit inside Rohn 65
and retrofits to a 3" mast without taking the antenna down and mast out
(big crane work).

Any experiences, products, ideas, designs welcome.  My shop is pretty
much able to make anything in metal.

Grant KZ1W

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