[TowerTalk] Ground Level Rotators

[Roger (K8RI) on TT]

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 at embarqmail.com>
> To: <towertalk at 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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