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Re: [TowerTalk] Ground Level Rotators

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Ground Level Rotators
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Sun, 08 Sep 2013 15:04:31 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 9/8/2013 1:08 PM, WA3GIN wrote:
I used this method on the HDBX48 and its been up for over 30 years.... funny thing is I've never had to work on the rotor (Tailtwister). I use a thrust bearing to keep the pipe weight off the rotor bearing although I'm sure they would handle the weight. I used allen screws to set the couplings. Abt 12sqft of antenna on the mast. I ran a ground strap from the mast coupling, just above the rotor, to ground.

I really like the innovative suggestions.

There is one thing I caution on and that is somr rotators are designed to work with a load on them and a negative load can be detrimental.

With the cable suspension, I's add a spline say from a car drive train. A good one with no slop, that would allow vertical movement of the mast and no negative (pull) on the rotator. The whole works would leave about 10# on the rotator so there would be no tendency to pull against metal with no bearings. Just keep it well greased.

Mounting the rotator independent of the tower removes all the torque from the tower so all it has to do is hold things upright. Of course this does put the entire torque load on the rotator, but it was designed for that.

There is, or can be, a problem with mounting the rotator to the tower near the base. The tower can no longer spread the torque along its length, but rather it now is between the rotator and the concrete almost all in shear mode. If mounted right at the bottom, it is all shear mode and unhealthy for the tower.

A local ham poured the pad a bit wider than needed. He then built a platform to fit inside the tower, but was entirely supported by two heavy steel angles (facing each other) bolted to the concrete. He used 2" X 3/16ths or 2" X 1/4 angle IIRC.

The platform was just an accessory shelf with the ears cut off to keep it clear of the tower. This was securely bolted to the steel angle.

Just think of two steel angles about 6 to 8 inches apart (what ever is convenient and fits) These bolt to the concrete roughly 6 to 8 inches outside the tower. They then go up a foot or so, then horizontally through the tower and back down on the other side. If tower bracing or construction prevents them from being at the same level, a block or riser can be fashioned to go on the lower one so they are at the same height where the rotator shelf mounts. Dimensions are not critical. For masting he used 2" Chrome molly with 1/2" wall. Heavy and over kill would be an understatement. I could not lift one end of a 24' length and I was doing full squats with 205# of free weight. We had to come up with a different rotator and he came up with a lighter mast.

One note on the mast being supported by cables that cause the mast to move vertically. This adds a varying percentage of the entire weight of mast and antennas to the rotational mass so the rotational torque varies through the rotational cycle. How much? I don't know as it depends not only the rotational angle (180 deg at max) plus the vertical angle to the anchor point. Higher is less.

I believe the tail twister is designed to support 500# dead load although it might be 800#. I'm sure some one on here will have the figure.

73

Roger (K8RI)

73,
dave
wa3gin
----- Original Message ----- From: "Wilson" <infomet@embarqmail.com>
To: <towertalk@contesting.com>
Sent: Sunday, September 08, 2013 12:41 PM
Subject: [TowerTalk] Ground Level Rotators


I love the pipe mast and cable suspension.

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