I used that product:
http://www.centa.info/?show=products&c=&nr=32
73
Peter, DJ7WW
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Thomson
Sent: Mittwoch, 4. Mai 2016 05:41
To: towertalk@contesting.com
Subject: [TowerTalk] Rotator Choice for Larger Yagi
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
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