[TowerTalk] Rotator Choice for Larger Yagi

[Bob K6UJ]

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 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
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