[TowerTalk] Rotor damage prevention

Tue Oct 25 08:49:55 EDT 2005

Hello Zig,

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 Zig, 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.

----- Original Message ----- 
From: "S. Markowski Jr." <km9m-zig at comcast.net>
To: <g3jvc at jcleeve.idps.co.uk>
Sent: Tuesday, October 25, 2005 2:07 AM
Subject: Re: [TowerTalk] Rotor damage prevention

> Hi John,  I've heard of this... if you have (or know of) any pics or 
> links, I'd much appreciate it.  I too have an Italian worm drive, 
> currently not up.
> 73,
> Zig - KM9M
>
> John E.Cleeve wrote:
>
>>Its dark now, raining hard, the wind is gusting, and ones mind, and eyes, 
>>turn to the mass of metal, moving at the top of the tower. Having had one 
>>rotor ruined by gusting wind conditions, with stripped spur gears. I 
>>decided to replace it with an Italian worm gear unit. I also decided to 
>>try and reduce the mechanical "shock" load placed on the "parked" rotor, 
>>during high, and gusting wind conditions, by fitting a rubber doughnut 
>>drive coupler, originaly intended as part of a Triumph prop shaft drive 
>>train, and bought as a new spare part, between the Italian rotor drive 
>>plate and the drive shaft to the Yagi. The rubber coupler assembly is 
>>enclosed and protected from the weather, and possible deterioration due to 
>>UV exposure. The yagi is moving gently in the gusts, with a six inch 
>>diameter, rubber doughnut absorbing the mechanical stress, I 
>>hope......just thought this might be of interest to the group...... 
>>regards..John. G3JVC
>>
>>--
>>This email has been verified as Virus free
>>Virus Protection and more available at http://www.plus.net
>>
>>
>>
>>
>>_______________________________________________
>>
>>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
>>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
>>any questions and ask for Sherman, W2FLA.
>>
>>_______________________________________________
>>TowerTalk mailing list
>>TowerTalk at contesting.com
>>http://lists.contesting.com/mailman/listinfo/towertalk
>>
>>
>>
>
> --
> This email has been verified as Virus free
> Virus Protection and more available at http://www.plus.net
> 