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Re: [TowerTalk] Tailtwister failure mechanism

To: <>
Subject: Re: [TowerTalk] Tailtwister failure mechanism
From: "Roger (K8RI)" <>
Date: Wed, 19 Sep 2007 13:32:06 -0400
List-post: <>

>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.

I started out with a Hy-Gain HDR-300 (IIRC) and went through two of those in 
a matter of months. It's not that anything broke, but I didn't dare move the 
array when there was much wind. Both times releasing the brake let the array 
windmill so fast the motor couldn't stop it and it went right on by the 
stops. Then I had to take the rotator down and reposition the innards.  With 
two of them I couldn't keep up with the failures.

So I ordered the PST-61 and while waiting for that I had a Tailtwister in 
there. It'd turn the array OK, but not in the wind. It just didn't have the 
power and it wasn't due to low voltage. So I basically used that one to hold 
the array in position.

> 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.

The only thing I can find fault with is having the rotator so close to the 
top of the tower.
If the thrust bearing is the only alignment I'd expect some very strong 
forces against the rotator with the thrust bearing acting as a pivot point. 
However, in none of these cases would I expect to find that shaft broken. 
The bell housing would have to be very loose for much of any lateral 
movement and even then I'd expect the gears to go and not the shaft.

Good Luck on finding the problem.


Roger (K8RI)
Does the thrust bearing do any alignment other than holding the mast 


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