Pinning the Mast to the Rotor using an Aluminum Rod (the softer stuff
not 6061) has the
similar effect as a Shear Pin. In extreme situations the pin "shears"
and the Rotor Gears
73, Dick, W1KSZ
On Thu, Apr 5, 2012 at 10:08 AM, K8RI <K8RI-on-TowerTalk@tm.net> wrote:
> On 4/5/2012 12:27 PM, Bob K6UJ wrote:
>> As I see my stack of beams swinging back and forth in the wind I am thinking
>> about adding a flexible shaft coupling above the rotor
>> to absorb the shock, I have read somewhere about using automotive drive
>> shaft flex couplings and adapt them to clamp on to
>> our 2" masts. I used to have one of Bill Orr, W6SAI books on antennas and
>> if I remember right he used one for a Volvo, and it
>> had a rubber donut between two flanges. Anyone make a flexible coupler for
>> their mast and would share what you used ?
> A flex coupler, like a long mast adds some unknowns. It may help and it
> may not.
> Both the couple and mast can add resonance which under the right
> conditions can increase the torque applied to the rotator tremendously.
> We think of masts as being rigid, but the longer they get the more give
> they have which is exactly how a torsion bar works. Normally it's not a
> problem, but the larger the array(s) and the longer the mast the more
> likely it is to end up resonating. With 40 feet of 2" mast (1/4" wall)
> and a large array http://www.rogerhalstead.com/ham_files/Tower29.htm on
> "some" windy days I'd see 10-15 degrees of twist between the bottom
> antenna and the rotator.
> Pinning masts is not "normally" recommended. As has already been
> mentioned, it's a whole lot easier to realign the mast, or direction
> indicator than to replace gears.
> Being blunt, I do not like rotators that use wedge brakes. I use them
> because they are cheap and work well most of the time for small antennas
> and they are relatively easy and cheap to rebuild. The array shown is
> pretty good size, but not huge. The whole thing is not as large as a 5
> or 6L 20M monobander, but it tore the guts right out of a tail twister.
> All too often these rotators are used with large antennas that are far
> beyond their capabilities. I expect to be able to turn what ever is up
> there whether the wind is blowing or not. On a windy day these rotators
> need to be de-rated substantially.
> Roger (K8RI)
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