Grant, please, check the "Flex Shock Mount Clamp";
http://www.ure.es/media/kunena/attachments/1956/3akp1012800x600.jpg
Available in many different
sizes, power and even colours (aka quality);
https://www.ktr.com/en/products/power-transmission-technology/couplings/flexible-jaw-and-pin-bush-couplings/rotex/rotex-standard/
73, Maximo
> To: jonpearl@tampabay.rr.com; k6uj@pacbell.net; towertalk@contesting.com
> From: grants2@pacbell.net
> Date: Wed, 4 May 2016 08:39:02 -0700
> Subject: Re: [TowerTalk] [Bulk] Re: Rotator Choice for Larger Yagi
>
> You ask a very important question. Can these handle the static axial
> load of mast and antennas?
>
> http://www.wholesaleimportparts.com/driveshaft.php for a picture of one
> with mating assemblies.
>
> A complexity is how the shaft (mast) is supported either side of the
> coupling as I don't think they are designed to handle large sideways
> torques or axial thrust - i.e. each shaft is held in alignment by two
> bearings which also control the axial dimension, which would not be the
> case in using one above a rotator and something else at the tower top.
> If the something else was a tube sleeve then it constrains the angle the
> mast can attain, but not the axial dimension. If the something else is
> the typical "thrust bearing" then the shaft can move to some surprising
> angles, but does have axial constraint. In neither case would a HyGain
> or Yaesu design rotator really be two bearings holding its output
> "shaft", except when the dead (axial) load is sufficient to keep the
> races tight under all circumstances. Other rotator designs have
> constrained shafts with two or more bearings.
>
> The common "Lovejoy" coupling is another version of a rubber isolated
> coupling in common use in many sizes. Again, it is used where both
> shafts are rigidly constrained radially and axially. A Lovejoy is
> specified to handle x degrees of misalignment and y thousands of an inch
> of shaft offset, at an rpm and torque value. I think those are the
> primary objectives, not shock absorption. A Lovejoy is not intended to
> take axial loads, so would be a bad choice without shaft constraints.
>
> The picture of the driveshaft components also leads me to suspect that
> pins, not bolts are the shaft to coupling connection, so the intent is
> no axial load on the rubber coupling.
>
> The link recently posted
> http://m4.i.pbase.com/v3/91/283791/1/50045854.P0001095.JPG shows a
> rubber coupler design with what appears to have solutions to the issues
> above. The tube above the rotator clearly doesn't turn and it appears
> to have a bearing at the end for the mast inside. Looking closely, it
> appears the end of the mast has a spline that mates with the top
> attachment to the coupling. Thus, no thrust load can be placed on the
> coupling.
>
> A tower with antennas is a very complex dynamic system - many masses and
> springs and few energy absorption elements. My reasoning is the shock
> and vibration loads cause the destruction from high amplitude
> oscillations or when hard stops are hit - rotator brakes and gears all
> have backlash. Loose mast and boom clamps and rotator bolts are another
> source. Peened out shear pin holes are a sure sign of problems.
> Another concern with a rubber isolator is it adds another spring (with
> low damping) into a system that has unknown dynamic properties. It is
> an offset to the benefit of the rubber isolator ability to reduce the
> peak torque values by spreading a shock pulse energy out over time.
> Another potentially large force can be created by adding a "balancing
> weight" at the end of a boom, so the boom is statically balanced at the
> mast attachment. However, that adds a weight on the end of a cantilever
> beam spring, when the other element masses are distributed along it.
> I've seen it done to ease of tramming the antenna, but adding to the
> rotational inertia is not good.
>
> One also might question what these couplings are really designed to do.
> Shock transients are large amplitude low frequency content events.
> Vibrations are small amplitude higher frequency and usually continuous.
> Rubber isolators generally don't have much damping at low frequencies,
> which are what I see when my aluminum starts waving around in a storm.
>
> Another idea is to adapt a rubber spring torsion axle as an isolator.
> These are used on smaller trailers and can handle loads in multiple
> axis. Again, with very limited damping loss.
>
> http://www.northerntool.com/shop/tools/product_200649004_200649004
>
> Grant KZ1W
>
>
>
> On 5/3/2016 23:01 PM, Jon Pearl - W4ABC wrote:
> > Hi Bob and Jim,
> >
> >
> > There's a whole bunch of videos on Youtube on their typical use, but
> > these two get to the point pretty quickly with some good close-ups:
> > https://www.youtube.com/watch?v=4yCxhyTlysw &
> > https://www.youtube.com/watch?v=v71KGSCjBrQ
> >
> > Bob - as to your prior question in the earlier email, I would imagine
> > any decent driveshaft shop could come up with 3 bolt flanges to weld
> > onto whatever you could drag into their shop and do so
> > concentrically. In searching, I see that there are also 4 bolt models
> > of flanges and flex joints. I would think that the 6 bolt versions
> > would provide more cushion for rotator purposes as there is more
> > rubber between the bolts.
> >
> >
> > I have a question about the use of one of these devices, though.
> >
> > Would it be possible or more likely *wise* to allow the weight of a
> > mast and antennas to come to rest directly on the flex joint,
> > compressing it (distorting it) between its two flanges? Its primary
> > function in automotive use is to reduce vibration through the
> > regularly anticipated twist of a drive shaft, not to be heavily
> > compressed between the transmission and pumpkin. I wouldn't mind
> > trying one of these flex joints, but I would hate to have to use a
> > bearing shelf, collar and bearing to hold the weight of the mast and
> > antennas off of the joint.
> >
> >
> >
> > 73,
> >
> >
> > Jon Pearl - W4ABC
> >
> > www.w4abc.com
> >
> >
> > On 5/4/2016 12:21 AM, Bob K6UJ wrote:
> >> Jim,
> >>
> >> Thanks for the good background info on the flex discs for our ant masts.
> >> I used to have Leesons book. Wish I still had it to check out his
> >> BMW flex disc
> >> configuration. I had to chuckle about M2 backing away from the
> >> flex discs. They have
> >> been used on automotive drive shafts for a long time, and as you said
> >> the locktite
> >> for the studs is standard procedure.
> >>
> >> Bob
> >> K6UJ
> >>
> >> On 5/3/16 8:40 PM, Jim Thomson wrote:
> >>> Date: Tue, 3 May 2016 19:05:25 -0700
> >>> From: Jerry Gardner <jerryw6uv@gmail.com>
> >>> To: Bob K6UJ <k6uj@pacbell.net>
> >>> Cc: towertalk@contesting.com
> >>> Subject: Re: [TowerTalk] Rotator Choice for Larger Yagi
> >>>
> >>> Interesting, Not being a "car guy" I've never heard of flex discs.
> >>> Do you
> >>> have any more info, perhaps a few links to websites describing them
> >>> and how
> >>> they can be used as part of an antenna/rotator system?
> >>>
> >>> 73,
> >>> Jerry
> >>>
> >>> ## The BMW flex disc is well documented in leesons book, physical
> >>> design of yagis...now out of print. It was a $25 part, available at
> >>> any
> >>> BMW dealer, looks like a giant rubber doughnut...without the hole
> >>> in the middle,
> >>> lol, and had 4 x threaded studs imbedded into the rubber.... at
> >>> each end.
> >>> IE: 4 on each end. The 4 at the front end are offset from the 4
> >>> at the back end,
> >>>
> >>> ## I believe BMW used the rubber flex coupler, in line with the
> >>> driveshaft on their cars.
> >>> It has just enough flex in it, when twisted in either direction, to
> >>> absorb tq.
> >>>
> >>> ## For rotor use, its mounted vertical of course, sandwiched
> >>> between 2 x al plates.
> >>> I think leeson then used a huge chunk of 90 deg angle AL, on both
> >>> the top and bottom
> >>> al plates , bolted. Then the long ant mas was U bolted to the
> >>> upper angle AL.
> >>> Then a real short, 1 ft long piece of pipe /tubing was U bolted to
> >>> the lower
> >>> angle al. ( which in turn is bolted to the bottom plate). Bottom
> >>> end of this 12 inch long
> >>> piece of pipe /tubing was inserted into the rotor in the normal
> >>> fashion.
> >>>
> >>> ## It worked superb, and provided just enough isolation, so when
> >>> yagi is at rest, and winds blowing,
> >>> the rubber flex disc absorbed the shock, vibration etc, so the teeth
> >>> in the rotor final gear don’t get trashed.
> >>> IE: the rubber flex disc absorbed a lot of the gear chatter /
> >>> backlash. The disc will also absorb the initial hit
> >>> of tq, both starting..and stopping. These days, most rotors have
> >>> ramp up and ramp down, so that part of it
> >>> is not a big issue.
> >>>
> >>> ## sad part of all this is... M2 in fact did make their version of
> >>> this disc assy, with heavy duty steel plates, and
> >>> the same finish as their m2 oem drive plate assy. The M2 version
> >>> used no angle al pieces at all, and the simple
> >>> sandwich was just bolted to the oem m2 drive plate. Oem m2 mast
> >>> clamp was then bolted to the upper steel plate.
> >>>
> >>> ## m2 stopped making the optional rubber doughnut isolation assy.
> >>> They told me, it was cuz folks...were not doing regular
> >>> maintenance on the assy. IE: the bolts that held the sandwich
> >>> assy, would work loose. Also the 8 x threaded BMW
> >>> studs would also work loose. Seems silly to me, since blue
> >>> loctite, or even red loctite would have solved that issue.
> >>> I pleaded with them at the time I bought the pair of OR-2800 rotors
> >>> to reconsider, and start making it again..but
> >>> to no avail. Their version was superb. Built like a tank.
> >>>
> >>> ## For automotive applications, the same 8 x threaded BMW studs
> >>> were always installed with blue loctite !
> >>> AFAIK, the BMW flex rubber couplings are still readily available.
> >>> Yaesu offered an optional rubber pad for their
> >>> big rotors, that was installed between the base of their rotor and
> >>> the mating steel triangular rotor plate in the tower.
> >>> The pad does little good, since it has its isolation at the wrong
> >>> end of the rotor.
> >>>
> >>> Jim VE7RF
> >>> _______________________________________________
> >>>
> >>>
> >>>
> >>
> >
> >
> > ---
> > This email has been checked for viruses by Avast antivirus software.
> > https://www.avast.com/antivirus
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|
