[TowerTalk] Ground Level Rotators

[Grant Saviers]

Roger makes a good point about many rotator bearings needing some axial 
load and the high axial loads they are rated for.

I would add a concern about the dead weight load imposed on the tower if 
a thrust bearing at the top supports the heavier mast sizes/materials 
discussed.  All tower specs I've seen have a dead load spec in addition 
to wind load.  Self supporting towers either fail in buckling,  
compression or tension of some structural element and excessive dead 
load may be a problem.  IMO, put the mast weight on the rotator and use 
a true radial bearing (wood, plastic, etc) at the top.  Then it is also 
easy to hoist the mast up a bit to remove the rotator.  (aren't the 
goals to make it easy to work on the rotator and take loads off the tower??)

Grant KZ1W


On 9/8/2013 12:04 PM, Roger (K8RI) on TT wrote:
> 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.
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>