[TowerTalk] flexible mast coupling

[Richard Solomon]

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
are unharmed.

73, Dick, W1KSZ

On Thu, Apr 5, 2012 at 10:08 AM, K8RI <K8RI-on-TowerTalk at 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.
>
> 73
>
> Roger (K8RI)
>
>
>
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