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Re: [TowerTalk] Flexible coupler assembly

To: "John E. Cleeve" <>,<>
Subject: Re: [TowerTalk] Flexible coupler assembly
From: "Dubovsky, George" <>
Date: Thu, 25 Jan 2007 13:50:04 -0500
List-post: <>
I designed one of the drive shaft couplers into my rotator system, based
on the suggestion in Dave Leeson's Yagi book. Mine was intended for a
BMW 1600, I think, and was bought off of the auction site for about $20.
I am told that all BMWs have something like this - do a search on
"guibo" and you will see what one looks like. If anyone knows where that
term comes from, I'd love to know!


geo - n4ua

> -----Original Message-----
> From: [mailto:towertalk-
>] On Behalf Of John E. Cleeve
> Sent: Thursday, January 25, 2007 1:30 PM
> To:
> Subject: [TowerTalk] Flexible coupler assembly
> Gentlemen,
> In view of the response I have received, permit me to publish a copy
> the
> email I sent to Dennis earlier today, also, I promise to obtain some
> close
> up digital photographs (Santa was thoughful!!) of the intstalled
> coupler
> assembly, when the tower is brought down for the summer
> John G3JVC.
> ----- Original Message -----
> From: John E. Cleeve
> To: N6KI Dennis Vernacchia
> Sent: Thursday, January 25, 2007 12:52 PM
> Subject: Re: [TowerTalk] rotors, controllers, etc.
> Hello Dennis,
> I can recommend this way of protecting the rotor. I had several
> experiences
> of teeth breaking in the spur gearing of the average "Jap" rotator,
> entirely
> due to the mechanical stress, and the backlash in their poor
> I
> have copied out the detail of the installation, originally for another
> member of the group, however, it does give a good idea of how I
> my
> then new, and very expensive rotator. The name of the manufacturer, of
> flexible coupler is "Metalastic", and you have to imagine a six inch
> diameter doughnut, with a section of about 1.5 inches, with six bolt
> holes,
> three to each coupling flange, in the transmission path of the
> You
> will have to do a little engineering, to couple this device into your
> antenna drive shaft. If you have a lathe, or, have a local engineering
> company make the necessary parts for you, then there is no problem.
> actual stores part number for this item is "Unipart" GCD 301. 62 Ne2
> 879407
> 19726, and the item is manufactured in the UK.  "Unipart" is the
> distribution system for Rover, Triumph etc. British cars. I bought the
> coupler as a new replacement spare part, and the cost was about 70
> sterling, plus our 17.5% value added tax, and it cost me about another
> pounds sterling "in pound notes!" to have some of the " metal turning"
> done
> by a local engineering company. Normally, this flexible coupler is
part of
> the drive train, ie drive shaft to the rear axle differential, used in
> Triumph TR7 sports car, and as such, more than able to cope with the
> torque
> stress applied by even force 12 gusting wind conditions in our
> applications......So, here you are, the detail, as I posted it to to
> reflector, I hope you find the information of some use....sincerely,
> G3JVC.
> I am sorry but I do not have any digital pictures, but I can give a
> description, so here goes:-
> The Italian worm drive rotor I have, is a PST medium range model. The
> rotor
> is bolted to a horizontal plate, which is part of the head unit, of my
> 60ft
> Strumech tower. The drive output of my PST rotor is a 4 inch diameter
> horizontal disk. and the rotary drive shaft to my yagi, is 2 inch
> construction grade aluminium tube, with a 0.25 inch wall thickness.
> rubber doughnut I used in my flexible coupler, normally forms part of
> Triumph sports car drive train, coupling the prop shaft to the
> differential.
> The outer diameter of the doughnut is about 6 inches, and its cross
> section,
> about 1.5 inches. The doughnut has six metal sleeved  holes through
> rubber, intended for three fixing bolts to each flange of the
> interconnected
> prop shaft.
> In order to make use of the doughnut, I had two aluminium discs cut,
> 7
> inches in diameter, and 0.5 inch in thickness ( it took about five
> minutes).
> The discs and the doughnut were very carefully centred. The discs were
> then
> clamped together and the three hole fixing pattern, for the concentric
> rotation of the doughnut, was drilled.
> One disc was then engineered to fit the 4 inch drive plate of the PST
> rotor,
> and the other disc, which forms the top, or drive disc, engineered to
> couple
> the yagi. In order to couple the 2 inch diameter drive shaft from the
> to the drive disc, a 6 inch long, 2.5 inch diameter bar of aluminium
> used, this bar was then bored 2 inches internal diameter, to a depth
of 5
> inches. The 2.5 inch diameter bar is then drilled and tapped with
> holes, at the blind end, and secured, concentrically, by stainless
> screws, to the top of the drive disc. The yagi drive shaft will then
> into the bored 2.5 inch bar, to a depth of  5 inches, this
> assembly is the drilled, 0.5 inch clearance, at right angles to the
> of
> the sleeve/shaft, and a 0.5 inch high tensile bolt  passed through the
> complete sleeve/shaft assembly. This works well, and will not "slip".
> In order to assemble the rubber doughnut coupling, six spacers were
> from 1 inch diameter aluminium, bored to take the doughnut fixing
> and
> of a length, to allow approximately 1 inch spacing between the inner
> of the two 0.5 inch thick discs and the sides of the rubber doughnut.
> complete drive chain is now  rotor/disc/doughnut/disc/driveshaft
> coupling/driveshaft/yagi. The yagi drive shaft then passes up through
> collar of the tower head unit, where the vertical load is taken by a
> roller thrust bearing, rescued from the rear axle of a huge tipper
> in
> our local scrapyard. The weather covering of the doughnut coupler
> is formed by wrapping a thin soft aluminium sheet, around the outer
> of
> the 7 inch discs, this soft aluminium sheet was a litho printing
plate, in
> another life. The weather shield is secured only to the edge of the
> disc, by means of a stainless steel, ducting strap. the weather shield
> extends down beyond the lower aluminium disc, by approximately 1 inch,
> thus
> enclosing the entire doughnut coupler assembly. All exposed metalwork
> been given several coats of Finnigans clear Waxoyl (prevents
> and
> stops ice forming in winter). As the doughnut flexes in taking up the
> load, the two coupling discs are able to gently move with respect to
> other. So, there you have it, I have done all I can think of, to
> the PST rotor, of any unnecessary mechanical stress, and I hope,
> prolonging
> its working life. I hope this information is of some use to you, and
> the group, for I am sure that many people wish to protect the
> both in time and money, which is exposed to the elements at the top of
> towers, and this was my way........sincerely, John. G3JVC.
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