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Re: [TowerTalk] Flexible coupler assembly

Subject: Re: [TowerTalk] Flexible coupler assembly
From: "Pat Barthelow" <>
Date: Thu, 25 Jan 2007 10:58:07 -0800
List-post: <>
I think Dave Leeson mentioned in his book, that he used a similar rubber 
donut steering coupler from a BMW automobile.  A Google  image search of 
"steering coupler"  brings up many examples:

73, DX, de Pat AA6EG;
Skype: Sparky599
Moon or Bust!--Jamesburg Gang Rides Again!

>From: "John E. Cleeve" <>
>To: <>
>Subject: [TowerTalk] Flexible coupler assembly
>Date: Thu, 25 Jan 2007 18:29:36 -0000
>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
>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, 
>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 
>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
>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 
>The outer diameter of the doughnut is about 6 inches, and its cross 
>about 1.5 inches. The doughnut has six metal sleeved  holes through the
>rubber, intended for three fixing bolts to each flange of the 
>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 
>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 
>and the other disc, which forms the top, or drive disc, engineered to 
>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, 
>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 
>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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