[TowerTalk] DX Engineering RT4500HD rotator

[Ken K6MR]

I worked for a guy in the 1960s (W6HX) who built prop motor rotators as
part of his antenna installation business.  The top gearbox seal does
nothing to keep water out.  The only way to keep the rotator dry is to have
a sheet metal "dog house" on top of the rotator plate surrounding the
entire top area.  His design had a selsyn as well as mechanical stops and
electrical limit switches which were all covered by the dog house.  A sheet
metal overhang seal was on the mast to seal the top of the cover where the
mast passed through the top.

Prop motors are not difficult to rebuild if the bearings are still
available.  I have not tried to find any for at least 40 years so I don't
know.  All the bearings have model numbers stamped on them for easy
identification.  The only bearing that was not available last I looked was
the large bearing that the bevel gear sits on.

*Ken K6MR*


On Sat, Jul 22, 2023 at 2:49 PM <john at kk9a.com> wrote:

> Some people have really good luck with K7NV prop pitch rotators and others
> like you have water related issues.  I do not know what the seal looks
> like.
> I do know that Kurt wanted the full weight of the mast and antenna on the
> rotator to seal the gear box, I am sure that you heard this and tried it.
> It
> is sad to hear that you have had so many rotator issues with the expensive
> rebuilds. That is not what you except out of a prop pitch. Two of my prop
> pitch motors are driving K0XG rings and those motors have the gearbox
> facing
> downward so they have different water proofing methods (I hope).
>
> John KK9A
>
>
>
>
> Paul Christensen w9ac wrote:
>
> I own a RT4500HD but waiting on cooler weather for installation.  It seems
> robust enough as it's replacing a small form-factor prop-pitch.  Between
> excessive water leakage after rebuilds and K7NV now SK, I was looking for
> an
> alternative.  The reliability of prop-pitch rebuilds has been
> disappointing.
> N4CC and I have been changing them out every 1-2 years at a cost of $2,500
> per rebuild.  Crazy.  We have a prop-pitch "graveyard" at our remote site
> with something like six prop-pitches needing repair.
>
> What seems to happen is that water ingress is caused by excessive surface
> heat in the Florida summers, followed by cool rain.  This creates a suck-in
> effect.  Because a prop-pitch is mounted upside-down in a tower, the seal
> needs better protection without having to resort to a special covering.  In
> this regard, the DXE rotator seems much better.  In fairness, the
> prop-pitch
> was designed for a different application. But yes, only time will tell.
>
> The first DXE rotator installation will turn a full-size 4L M2 40m monoband
> Yagi at 140 ft and a 9L M2 6m Yagi at 155 ft.  Both antennas are mounted on
> a 3-inch chromoly mast.  This fits within the DXE design spec.  In
> preparation for the installation, we used a crane back in April to change
> out a Rohn 3-inch thrust bearing with the equivalent type from DXE.  The
> DXE
> bearing seems much more robust.
>
> Paul, W9AC
>
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