At 02:52 PM 9/17/2006, K8RI on TowerTalk wrote:
> >From: "Jim Lux" <jimlux@earthlink.net>
>
> > 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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