----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
> 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
> 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 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
> 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 agree, Jim.
If there is any benefit to a second bearing, it would be reduction of
the side load that is transferred to the rotator by the antenna side
load when the top bearing behaves as a fulcrum. If the ratio of the
out-of-tower mast length to the in-tower length is large, this force
could be substantial., especially with a big array topside (this fact
argues for keeping a long length of mast inside the tower).
In any case, the top bearing removes the axial load from the rotator
and the 2nd bearing working in combination with the top bearing
would remove the radial load (assuming good alignment) leaving
only the rotational force (i.e. torque) for the rotator to handle. Of
course there is no reason that the rotator can't incorporate an
effective thrust bearing eliminating the need for an external #2
thrust bearing (except that the external 2nd bearing is nice when
doing rotator servicing). The extent to which various rotators are
also good thrust bearings is what seems to be in question.
73, Mike W4EF..................................................
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