----- Original Message -----
From: "Dan Zimmerman N3OX" <n3ox@n3ox.net>
To: <towertalk@contesting.com>
Sent: Monday, November 20, 2006 1:30 AM
Subject: Re: [TowerTalk] mast weight on the rotor or thrust bearing?
> >Actually I think the old, cheap, TV towers had it right. They had a
> >sleeve
>>at the top and that served as a "side" thrust bearing.
>
> I'm wondering something, as someone who's spent graduate school
> building big machines, but also someone who's never done anything
> with a real tower.
>
> It seems to me that a good approach would be a tower section with two
> good bearings mounted in it, one for radial forces only (the top one)
> and one for axial and radial forces on the bottom, and then the
> rotator would JUST rotate and brake, with a flexible coupler between
> the rotator shaft and the mast.
That topic was on here about a month or two back. We were talking about
using a spline in the shaft above the rotator. That would allow for
vertical movement when properly adjusted, and allow for the thrust (vertical
and horizontal) to be handled seperately.
In my case the antennas and mast extend well above the top of the tower
while the rotator is well down in the
http://www.rogerhalstead.com/ham_files/Tower29.htm
tower. This has allowed the thrust bearing to serve as a pivot for the side
thrust. So when the wind blows (and flexes) the top section to the north the
section under the thrust bearing pushes (and flexes) south. As the ratio
above the thrust bearing to below is about 2:1 this puts a lot of side force
on the bottom of the mast, but the forces at the pivot point are very
strong. In this case the sleeve *should* prevent, or at least reduce the
flexing and raise the resonant frequency of the system substantially. It
also increases the area supporting the side load by over one if not two
orders of magnitude. Those thrust bearings are expensive to only last 4 or
5 years. Using the sleeve is much less expensive, but it involves developing
an adjustable mount for both the top and bottom of the sleeve. It's also
heavy.
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com
>
> Are people doing it, and I just don't know, or is there some practical
> advantage to having your lower bearing be custom-built into the
> rotator housing?
>
> 73 from an eventual tower owner,
> Dan
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