I agree, Tom. K Factor and absolute limits have nothing in common,
except that is the present day way of rating the rotor and was also the
primary concern of Frank's original message. Is his system going to
crash and burn, probably not. Is the K Factor a good approach to the
selection of a rotator, probably not, but it is today's method. You are
correct in saying that a better system of rating is still needed.
My point was that if his selection makes him uncomfortable as to the
safety of this rotator because of a calculated narrow margin of reserve
K factor, or maybe none now considering the weight of the mast, he
would sleep better and likely have more security with a rotator with a
larger capacity. In the case of rotators, bigger ratings usually mean
better and longer service life, with the T2X tailtwister being the only
exception I'm aware of. I don't wish to start another thread, and I have
never owned a T2X, but I believe the majority of the Hygain/ CDE bell
rotator "problems" occur from improper mast centering and the lack
of appropriate use of shims to achieve concentricity between the mast
and the rotor's fixed center,... but that's another whole subject that has
been debated since the 50's, when the HAM-M's first became available.
----- Original Message -----
Cc: <K7NV@Contesting.com>; <K7LXC@aol.com>; <FrankNorton@home.com>
Sent: Wednesday, July 11, 2001 9:23 AM
Subject: Re: [TowerTalk]
> Are you implying that the K factor is some kind of precise
> engineering number that accurately represents the moment
> of inertia of a rotating antenna? I hope not. There can be
> HUGE differences in moment of inertia based on the
> DISTRIBUTION of the weight. For example a 2 element
> low band yagi places all of the element weight at the ends
> of the boom and would have a higher moment of inertia than
> a multi element tribander or high band monobander on the
> same length boom where both antennas have the same weight.
> K factor is nothing more than a CRUDE GUESS at rotor capability,
> just as the old (empirical) ratings based on boom length were
> GUESSes of rotor capability.
> The moment of inertia for any mast will be nearly insignificant
> because even though it may have a large weight, it's radius is
> VERY SMALL compared with the turning radius of the antennas.
> A heavy mast can easily weigh as much or more than a large
> antenna but the moment of intertia of the antenna will greatly
> exceed the moment of inertia of the mast.
> K factor and "absolute limits" have nothing in common.
> A better system is STILL needed.
> Tom N4KG
> On Wed, 11 Jul 2001 "Roger Borowski" <K9RB@bellsouth.net> writes:
> > If your calculations are so close to the limitations of the G1000DXA
> > without the
> > inclusion of the mast, and the mast weight pushes any safety margin
> > over the
> > limitations for this rotor, you should have used a larger rotator,
> > especially if
> > you
> > are uncomfortable now! Its never good practice to "engineer"
> > mechanical things
> > to near their absolute limits. When doing so, short life and
> > failures are
> > inevitable!
> > -=Rog-K9RB=-
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