[TowerTalk] Rotator Choice for Larger Yagi

[Jim Thomson]

Date: Tue, 3 May 2016 19:05:25 -0700
From: Jerry Gardner <jerryw6uv at gmail.com>
To: Bob K6UJ <k6uj at pacbell.net>
Cc: towertalk at 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