At 10:53 AM 9/12/98 -0400, K7LXC@aol.com wrote:
>In a message dated 98-09-12 10:37:12 EDT, n7ex@athenet.net writes:
>
>> Explain how you would calculate the side loads on the rotator in both cases
>> below.
>>
>> First case: The weight of the mast supported by the thrust bearing,
>>
>> Second case: Weight of the mast supported entirely by the rotator, Assume
>> the mast has minimal (few thousandths) of play where it goes through the
>> top of the tower.
>>
> The mast is the lever arm and the pivot point is where it contacts the
>top of the tower. The mast and antenna load is trying to pry the bottom of
the
>mast that's attaced to the rotator in the opposite direction with LOTS of
side
>force.
>
>Cheers, Steve K7LXC
Steve et all
That's the way I saw it too. Seems to me that (to K6LL's point) given
equal set ups in case 1 and 2, i.e. same mast, same rotator mounting point,
same antenna mounts etc.,that the horizontal moment on the rotator is the
same (or very close, depending on the play in the thrust bearing) with or
without the thrust bearing supporting the mast. My open query to N4KG (and
the reflector) was to be sure that I hadn't missed something.
I suppose however that it is possible that the DISTRIBUTION of horizontal
forces could be slightly different INSIDE the workings of the rotator for
the two cases, This distribution of forces might also be a function of the
design of the rotator. In the second case the bearings are certainly in
greater compression and this might result in a more efficient (?) transfer
of horizontal forces to the bearing surfaces rather than other parts of the
rotator which may not be designed to take them as well.
I suppose in a situation where there was lots of play (say 1/4 inch or more
at the top) in case 2 that you could get some interesting moments with both
a Y and a Z component depending on how much the mast flexes. This I think
is probably not a desirable situation for the life of the rotator. This
would also depend on the distance from the rotator to the top (pivot point)
of the tower and the flex ability of the mast, etc etc.
Dave
K9NX
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