[TowerTalk] Rotator Choice for Larger Yagi

Wed May 4 02:01:58 EDT 2016

Hi Bob and Jim,

There's a whole bunch of videos on Youtube on their typical use, but 
these two get to the point pretty quickly with some good close-ups: 
https://www.youtube.com/watch?v=4yCxhyTlysw & 
https://www.youtube.com/watch?v=v71KGSCjBrQ

Bob - as to your prior question in the earlier email, I would imagine 
any decent driveshaft shop could come up with 3 bolt flanges to weld 
onto whatever you could drag into their shop and do so concentrically.  
In searching, I see that there are also 4 bolt models of flanges and 
flex joints.  I would think that the 6 bolt versions would provide more 
cushion for rotator purposes as there is more rubber between the bolts.

I have a question about the use of one of these devices, though.

Would it be possible or more likely *wise* to allow the weight of a mast 
and antennas to come to rest directly on the flex joint, compressing it 
(distorting it) between its two flanges?  Its primary function in 
automotive use is to reduce vibration through the regularly anticipated 
twist of a drive shaft, not to be heavily compressed between the 
transmission and pumpkin.  I wouldn't mind trying one of these flex 
joints, but I would hate to have to use a bearing shelf, collar and 
bearing to hold the weight of the mast and antennas off of the joint.

73,

Jon Pearl - W4ABC

www.w4abc.com

On 5/4/2016 12:21 AM, Bob K6UJ wrote:
> 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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