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Re: [TowerTalk] Fw: Rohn 45 Question

To: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Fw: Rohn 45 Question
From: "Roger (K8RI)" <K8RI-on-TowerTalk@tm.net>
Date: Sat, 25 Aug 2007 22:48:19 -0400
List-post: <mailto:towertalk@contesting.com>


> At 01:29 PM 8/25/2007, Ron Todd wrote:
>>So why does a rotator want to have that second thrust bearing?
>>
>>I wanted two because when you take the rotor out and with only one thrust
>>bearing you don't have control of the mast horizontally. With two TB you
>>always have control.
>
>
> I assume what we're talking about here is a bearing to take a radial
> load as opposed to an axial load, or perhaps both (i.e. like a wheel
> bearing on a car).  I can see that having two bearings and having the
> rotator floated so it can translate, but not rotate, relative to the

Most of the rotators I've seen (and I'm a long way from seeing them all) 
really need a load in the vertical plane for their bearings to work the 
properly.

> tower, could essentially remove all the non-torque loads from the
> rotator.  Heck, you could use a belt or chain drive to the mast in

That works, but it translates all force to the rotator as an amplified side 
force.
Any torque applied to the chain will pull the output of the rotator 
sideways.

> that case, or even a friction drive, if you had a position encoder on
> the mast.  Maybe if you had a "too small" rotator (e.g. you bought it

The pot in the rotator will work just fine unless there is something other 
than a 1:1 gear ratio. Even then some rotators have a multi turn pot.

> many moons ago, and have been adding antennas over the years, and now
> it's way overloaded) being able to take up the bending and axial
> loads would help.

I believe most ham installations are small enough that this is seldom a 
problem percent wise. The problems come when
 someone starts moving up the ladder to larger antennas and towers while 
still using the same procedures they used with the simple set up. We see the 
same thing in aviation.  The 100 MPH mind in a 200 MPH airplane, or the 
money to purchase a P-51 while they have the mind set and reflexes to fly a 
Piper Cherokee.
>
<snip>
> Jim, W6RMK

73

Roger (K8RI) 

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