On Thu, Apr 5, 2012 at 1:14 PM, Richard Solomon <dickw1ksz@gmail.com> wrote:
> 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
>
>
If the aluminum pin does shear, the array can "windmill" and the control
cable and coax can suffer! I had to replace both after a similar event.
73,
Ken - K4XL
> 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.
> >
> > 73
> >
> > Roger (K8RI)
> >
> >
> >
> > _______________________________________________
> >
> >
> >
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--
Ken - K4XL
BoatAnchor Manual Archive
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