[TowerTalk] Rotator cage design

K8RI K8RI-on-TowerTalk at tm.net
Wed Jun 13 23:37:21 PDT 2012

On 6/14/2012 2:02 AM, Rick Kiessig wrote:
> I understand that rotators are not designed to handle lateral loads, and
> that I should therefore have the rotator on one shelf, then a second shelf
> above that with a radial support bearing on it, to handle the lateral loads.
> The most likely antenna at the moment (still a moving target) weighs 29kg,
> with a 7.2 sq ft wind load and a 6m turning radius. Kurt K7NV suggested
> welding two plates on the side of my pole/tower, at the top, a few feet
> apart. Does anyone know of existing designs/drawings for that kind of thing?

I'd be a bit cautious about welding things to the side of a tower, but I 
don't know what type of tower you have.  What type and size of tower do 
you have?  Welding to tubing and galvanized tubing takes skill.  it's 
very easy to weaken or even blow holes in the the structure by welding 
and even more so with some alloys.  BTW it's easier if you use the same 
units such as feet or meters, but don't mix them.  What are the boom and 
element lengths? Those are as important as turning radius.8

Many rotators will handle a lateral load, they just won't handle near as 
much as they will using thrust bearings.  The specs for the rotator 
should list the lateral load capability but if not, I'd give the 
manufacturer a call to see if they can give you a figure.

I'm building a bracket to mount the rotator outside the tower to drive 
the mast which is internal, but the rotator is about 40 feet below the 
top of the tower so it should not present an off center load.  There are 
other factors to take into account  as mast torque will translate to an 
unequal lateral load on the tower at the rotator location. With the 
rotator and mast mounted external at, or near the top it will present an 
asymmetrical load on the tower which may or may not be a problem 
depending on the size and capabilities of the tower.


Roger (K8RI)
> 73, Rick ZL2HAM
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