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Re: [TowerTalk] Flexible coupler assembly

Subject: Re: [TowerTalk] Flexible coupler assembly
From: Jan Erik Holm <>
Date: Thu, 25 Jan 2007 20:50:10 +0100
List-post: <>
Sounds like you mean a Hardydisc. I have used one on one of my rotating 
towers for years, my unit came from a Ford Granada station wagon.
Sure is a good way to protect a rotor. By the way, also to
get away from the problem in getting everything centered/lined
up exactly I incorporated a u-joint from the same car, then the
stuff can flex or wobble around and would not hurt the rotor.

73 Jim SM2EKM
Dubovsky, George wrote:
> 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!
> 73,
> 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
> of
>> the
>> email I sent to Dennis earlier today, also, I promise to obtain some
>> close
>> up digital photographs (Santa was thoughful!!) of the intstalled
> flexible
>> coupler
>> assembly, when the tower is brought down for the summer
> check........73,
>> 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
> engineering.
>> 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
> protected
>> my
>> then new, and very expensive rotator. The name of the manufacturer, of
> the
>> flexible coupler is "Metalastic", and you have to imagine a six inch
> outer
>> 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
> vehicle.
>> 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.
> The
>> 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
> spares
>> distribution system for Rover, Triumph etc. British cars. I bought the
>> coupler as a new replacement spare part, and the cost was about 70
> pounds
>> sterling, plus our 17.5% value added tax, and it cost me about another
> 50
>> 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
> the
>> 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
> the
>> reflector, I hope you find the information of some use....sincerely,
> John
>> G3JVC.
>> I am sorry but I do not have any digital pictures, but I can give a
> verbal
>> 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
> diameter
>> construction grade aluminium tube, with a 0.25 inch wall thickness.
> The
>> rubber doughnut I used in my flexible coupler, normally forms part of
> a
>> 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
> the
>> 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,
> each
>> 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
> yagi
>> to the drive disc, a 6 inch long, 2.5 inch diameter bar of aluminium
> was
>> 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
> three
>> holes, at the blind end, and secured, concentrically, by stainless
> steel
>> screws, to the top of the drive disc. The yagi drive shaft will then
> slide
>> into the bored 2.5 inch bar, to a depth of  5 inches, this
> sleeve/shaft
>> assembly is the drilled, 0.5 inch clearance, at right angles to the
> axis
>> 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
> made
>> from 1 inch diameter aluminium, bored to take the doughnut fixing
> bolts,
>> and
>> of a length, to allow approximately 1 inch spacing between the inner
> faces
>> of the two 0.5 inch thick discs and the sides of the rubber doughnut.
> The
>> complete drive chain is now  rotor/disc/doughnut/disc/driveshaft
>> coupling/driveshaft/yagi. The yagi drive shaft then passes up through
> the
>> collar of the tower head unit, where the vertical load is taken by a
> large
>> roller thrust bearing, rescued from the rear axle of a huge tipper
> truck
>> in
>> our local scrapyard. The weather covering of the doughnut coupler
> assembly
>> is formed by wrapping a thin soft aluminium sheet, around the outer
> edges
>> 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
> top
>> 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
> has
>> been given several coats of Finnigans clear Waxoyl (prevents
> corrosion,
>> and
>> stops ice forming in winter). As the doughnut flexes in taking up the
> wind
>> load, the two coupling discs are able to gently move with respect to
> each
>> other. So, there you have it, I have done all I can think of, to
> relieve
>> 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
> also,
>> the group, for I am sure that many people wish to protect the
> investment,
>> both in time and money, which is exposed to the elements at the top of
> our
>> towers, and this was my way........sincerely, John. G3JVC.


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