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
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