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Re: [TowerTalk] Recommendation for mast on bottom mount rotator

To: "K8RI on TowerTalk" <>,<>
Subject: Re: [TowerTalk] Recommendation for mast on bottom mount rotator
From: Jim Lux <>
Date: Sun, 17 Sep 2006 15:23:10 -0700
List-post: <>
At 02:52 PM 9/17/2006, K8RI on TowerTalk wrote:

> >From: "Jim Lux" <>
> > I would use some sort of spline coupling between torque tube and
> > antenna mast.  Perhaps not an actual spline, but something that works
>I think Jim's idea of the spline has some real possibilities.  If each shaft
>were fitted with a spline (male one end and female the other) it could
>eliminate a number of problems. Yes, it'd take fair amount of prep work, but
>the more I think about it the better I like it. Water is going to get in so
>some form of elimination would be needed and possible rust/corrosion inside
>the mast sections would needed to be taken into consideration.

bottom of tube has female spline, top has male, so water will tend to 
shed.  I suspect that in a real application, though, it would tend to 
rust, cold-weld, gall, etc.

> > similarly.  Depending on the amount of length variation, one of those
> > elastomeric spider couplings might work very nicely. They allow a
> > fair amount of angular misalignment, some axial play, but still
> > transmit the power.  (They look sort of like a U-joint/Cardan joint,
> > except the middle cross thing is flexible)
>With a spline joint at the end of each 20 to 24 foot mast it would make
>assembly much easier.  Bearings or
>bearing blocks could be used at each end to keep the masts centered. They
>would also allow for about any combination of top and bottom support.  It
>would require extra rotator/thrust bearing supports, but the bearings could
>easily be a couple of oil soaked hard wood blocks except for the ones that
>are load bearing.

Exactly.. they're just there to keep things "roughly" upright.

>   One point I really like is the ability to take out and
>install individual 20 to 24 foot sections with my existing gin pole and no
>more having to weld sections together inside the tower.

I wonder if you could use those inexpensive 4' fiberglass mast 
sections.  They have keyed interconnections, so, can transmit a torque.

> >
> > Like many mechanical engineering problems, there's lots of ways to
> > solve it, and the "right way" is probably more determined by the
> > materials and manufacturing technology you have available.  I have a
> > friend who truly believes in hydraulics for everything.  He'd
> > probably suggest putting a hydraulic motor up top and a pump down
> > below.  (A 5HP motor/pump is pretty small..a couple inches or three
> > on a side.)
>Aircraft landing gear pump
> >To that, I'd just ask how much kitty litter he's going
> > to buy to absorb the inevitable leaks as they drip down the tower.
>Think of it this way. If the pipes are properly oriented he'll never have to
>worry about rust.  Maybe this'd be a good approach for those near salt
>water? OTOH it could make tower climbing more than a bit interesting.<:-))
> >
> > Pneumatics?
> >
>Having worked in industry for many years in earlier careers I have learned
>to detest pneumatics and particularly the sound of pneumatic power tools
>although I do use them quite a bit. Pneumatics are easier to use and much
>more reliable than hydraulics in many applications, BUT they do have some
>short comings beyond being noisy. Position control does require pneumatic
>motors rather than pistons and these things require oil. Actually most of
>them require an oil mist in the air.  Pneumatic systems out in the elements
>are subject to freezing which means adding an air dryer to the system along
>with the previous mentioned oiler. That means a well maintained pneumatic
>system is likely to be messy.

And, the big problem is that pneumatics are inherently 
"springy".  unless you're actuating into a mechanical stop, that 
bites you eventually.

> >
> >> >As an off the wall idea.. have you considered using wood?  You can
> >> >get long straight round poles.  I haven't done any calculations of
> >> >relative strength, but it might be a possibility.
> >>
> >>Hadn't thought of using wood. My gut feeling says not to, but it's
> >>worth thinking about.
>=I think the wood would be strong enough, but probably far too springy.

OK, wood with fiberglass or carbon fiber.  Composites are always 
sexy.  Any ham can bolt in a steel mast, but how many can boast of a 
"hand laid carbon fiber epoxy composite on a organic mandrel".  I 
agree that torsional stiffness is important (after all, after you've 
aligned to true north within seconds of arc, why throw it away on 
sloppy mechanics).

Or, for a more primitive approach, bone and sinew, like high 
performance archery bows of yesteryear.


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