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Re: [TowerTalk] Tailtwister failure mechanism

To: <>, <>
Subject: Re: [TowerTalk] Tailtwister failure mechanism
From: "jeremy-ca" <>
Date: Wed, 19 Sep 2007 10:03:12 -0400
List-post: <>
Strange indeed.

For several years I used a T2X to turn a 10 15 20 stack of 4 el, the 20M 
being on a 40' boom. The T2X was down about 7' with a TB3 on the flat top 
and a home brew version made from a truck axle bearing just far enough above 
the rotator so it could be removed. The mast was about 24' of 1/4" wall DOM.

Only problems I had was slow turning in sub zero weather and wind and that 
was due to voltage loss in the cable. That rotator is still in service at 
this QTH.

Im not a ME ( but have built several dragsters and racing engines and 
understand the principles well enough) but possibly you have more side 
thrust than you expect. How high above the bearing is the yagi? How much 
side kick is there on the mast when you remove the rotator clamp?


----- Original Message ----- 
From: "Steve London" <>
To: <>
Sent: Wednesday, September 19, 2007 8:46 AM
Subject: [TowerTalk] Tailtwister failure mechanism

>I have had 2 Tailtwister failures in the past 3 months with the same T2X, 
> antenna, same tower. What is puzzling is that the failure mechanism has 
> been the
> same both times, and I haven't previously seen this kind of failure.
> In both cases, the gear shaft has broken. The gears themselves are fine - 
> no
> broken teeth, etc. What I don't understand is how there are any 
> significant
> forces on the gear shaft. The gear shaft is supported by the brake housing 
> on
> one side and the motor bracket on the other side. I just don't see where 
> the
> shear force is coming from.
> And, yes, I'm turning a fairly big antenna with it - 5 el 20, 40' boom. 
> The
> rotor is about 2 feet down from the top of the tower. The full weight of 
> the
> antenna is on the rotator (about 90 pounds), with a homebrew thrust 
> bearing to
> limit the lateral forces.
> Please, no bashing of CDE, HyGain, MFJ, or my stupidity in trying to use 
> such a
> small rotator to turn such a large beam. Constructive comments only !
> 73,
> Steve, N2IC
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