[TowerTalk] Add on 3" mast brake?

[Grant Saviers]

 > 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 at 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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