[TowerTalk] Rotator Choice for Larger Yagi (Couplers)

[Jon Pearl - W4ABC]

Thanks for posting that, Bob!  I was just gonna say...


I've been reading and researching different couplers as I'm making my 
way down through part of today's emails and I started to do some 
re-thinking on the subject.  I started to ask myself if there might be 
some advantage to moving a flexible coupler down, directly onto the top 
of the Orion mast plate rather than placing it up above the rotator's 
mast clamp where it would be forced to deal with more axial forces.  
 From my own reasoning, (and I may be wrong) viewing this picture 
http://www.its.caltech.edu/~w6ue/KT/OR-2800-2.jpg leads me to draw some 
conclusions:

  * No three fingered drive shaft ends need to be incorporated into the
    design to attach to the flexible coupler.
  * Axial loads are shifted downward, closer to the rotator.
  * Full mast and antenna weight can be applied to the flexible coupler
    as its distortion is limited to a small amount of sag - held in
    check by the OR-2800's OEM mast plate.  It's essentially a steel and
    rubber sandwich.


The issue of loose nuts and bolts is an interesting one as you're 
attempting to tighten the pair over a compressible rubber donut. Why 
don't they come loose and fall off of automobiles?  It may still come 
down to the presence of annoying axial loads as Grant has eluded to.



73,


Jon Pearl - W4ABC

www.w4abc.com


On 5/4/2016 1:25 PM, Bob K6UJ wrote:
> Grant,
>
> From what I read their main function is to dampen the torsional shock 
> loads.
> Here is what Mercedes Benz says:
> "The flexible discs serve two functions on the vehicle.  Primarily to 
> absorb excessive torsional shock applied to the drive shaft under hard 
> acceleration and deceleration.  They also isolate the drive shaft from 
> vibration while still transferring power from the transmission to the 
> differential. "
>
> Jon,  W4ABC brought up an interesting consideration.  Unless they are 
> isolated from the
> axial load involving the mast and antennas the disc will be supporting 
> the load.  Will they do their
> dampening job when they are supporting a load ?  Doesn't sound like 
> they would.
> In my case I will be supporting 99% of the load from the thrust 
> bearing above.  So probably not a concern.
>
> Lastly found this interesting post from the Tower Talk archives. Seems 
> the bolts coming loose is a
> common issue.
>
> 73,
> Bob
>
> Hi Jim,
>
> Warren, KE6LEA and I built one these flex-disc shock mount for one of the towers
> at the Caltech Amateur Radio Club. We used a Mercedes-Benz Flex Disc (a.k.a.
> Hardy Disc) coupled on one end to the output spindle of an M-Squared Orion
> OR-2800 rotator, and a homebrew steel mast clamp flange on the other. The system
> is used to turn a KLM 4el 40M yagi and KT-34XA both with the heavy duty
> boom options (~ 300 lbs of antenna). Our first inspection of the installation
> earlier in the summer revealed that several of the grade 8 flange bolts had fallen
> out of the steel flange, so we added a set of grade 8 jam nuts to each of the
> 6 flange bolts. After getting a considerable workout in Sweepstakes and CQ WW,
> I need to go back up the tower sometime soon and inspect all the hardware
> to see if anything has loosened.
>
> You can see pictures of the setup athttp://www.its.caltech.edu/~w6ue/antenna-pictures.html 
> <http://www.its.caltech.edu/%7Ew6ue/antenna-pictures.html>
>
> 73 de Mike, W4EF.............
>
>
>
>
> Bob
> K6UJ
>



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