Date: Thu, 05 Apr 2012 21:41:20 -0500
From: John Becker <johnb3030@comcast.net>
Subject: Re: [TowerTalk] HAM IV rotor / mast slipping / Slipp-Nott
The Slipp-Nott at first seems like a good idea, but as I found it can
put too much stress on the rotor U-bolts. If I had thought to double-nut
the U-bolts, that should have prevented the nuts from being unscrewed,
but it might have caused the upper U-bolt to fracture instead. If the
mast is slipping in the rotor clamp, that force is transferred through
the Slipp-Nott brackets to the rotor U-bolts, which are not intended to
withstand that kind of load. BTW, I know of another ham nearby who also
had a Slipp-Nott failure, but I don't know exactly what happened to his
installation.
My suggestion is to use a torque wrench to tighten your rotor U-bolts to
the maximum torque allowed and see if this helps. See
http://www.engineershandbook.com/Tables/torque.htm
http://www.engineershandbook.com/Tables/torque3.htm
and http://www.zerofast.com/torque.htm
73,
John, K9MM
## use nylock nuts, then you don’t need to double nut anything.
## use marine grade never-seize, then you only require about 60% of normal
torque.
Torque and tightness on a bolt is 2 completely different things.! You can
read all about
that on portland bolt’s website.
## At one of our stores, you can get this sticky back heavy duty non skid
stuff, used for
decks on boats and steps etc. Come in 1-2-3” wide rolls. They sell it by
the foot. It’s
used on my tic ring troughs. Wrap some of this around the mast, and it will
never slip. Put
some more on the mating clamp, so the two face each other, and it flat out
won’t slip.
## I used K7NV’s software to design the hb torque compensation plate. I
designed one for
a fellow who has a 5 el 20m yagi on a long boom. He has a mile more boom on
one side of the
mast vs the other side of the mast. The small AL plate was mounted in the
vertical plane, just
in front of the REF. We tested it on his short 30’ tower, with just 2 x
bearings and NO rotor.
In a high wind it just stayed put, it would NOT windmill at all. We even
climbed up there during the
high wind, and repositioned the yagi. It still would not budge. AND you could
turn it by hand !
## OK, same yagi, minus the TQ comp plate, on his taller tower, and all bets
are off. With no tq
comp plate, it ripped the gears out of his tail twister ! Method #2, mount
the yagi so you have equal
amount of boom on each side of mast, then insert a counterweight in the light
end of the array. K7NV’s
software will figure that weight out as well, slick program. And either method
works.
## If you don’t want to add TQ comp to your array, you have 2 x choices.
Kiss your rotor goodbye,
or get a bigger rotor.
## These rinky dink rotors like ham 4 and tail-twister really are a joke,
just look inside em. Wedge
brakes are 1959 technology, literally. Worm gears and double worm gears can’t
budge. They work just
like a hose clamp or the tuning adjustments on a stringed instrument.
## 800 in lbs of torque on a ham-4 = 800 divided by 12 = 67 ft lbs of TQ.
67 ft lbs of TQ is 3 x steps
below adequate. I can easily get 200 ft lbs from just a 2’ long TQ wrench.
And your boom is a lot longer
than 2’. 1000 in lbs from a tail twister = 83 ft lbs TQ Also a poor joke.
A small prop pitch is 1200 ft lbs TQ.
Now that’s the real deal. The OR-2800 is good (when used with either the
K7LXC clamp or the K7NV clamp)
as is the Prosistel rotors. Any other big rotor is good too. tearing up a
small rotor saves you nothing. You either
pay to rebuild it, or replace it. Now you are paying twice. Just get a
bigger rotor in the 1st place.
## trying to turn some huge array with a tail twister is fubar. I can’t
believe how cheap hams can get. Regardless
of rotor, at least use some TQ compensation. If you look at say F-12’s
specs, they will show you how much TQ to
expect. beware, that is for a 70 mph wind. Impact pressure goes up the SQUARE
of the wind speed. An 83.6 mph
wind will have 50% more pressure vs a 70 mph wind. A 83.6 mph wind will be
TRIPLE the pressure of a 50 mph wind.
A 100 mph wind is QUADRUPLE the pressure of a 50 mph wind. 99% of these
rotor to mast clamps are a joke. teeth
will not bite into a chromolly or DOM mast. The K7NV version is the real deal.
Mast won’t slip at all in his.
## the BMW rubber doughnut is a good idea. It’s there to prevent vibration
and shock loading of the gear train inside the
rotor. if the mast sits there and vibrates, the vibration wont get past the
rubber doughnut. Yaesu has a similar idea, a pad,
placed between base of rotor and rotor shelf. It achieves nothing , since it
is not between mast and rotor.
## dunno if BMW et all has that rubber doughnut with the 4 x embedded studs
sticking out each side still available or not.
The 4 on one side are not in contact with the 4 on the opposite side. I have
never see the doughnut used on north american cars.
Most will use either either a universal joint or a CV joint. (each end of the
driveshaft on a rear wheel drive car).
## use big wire for the rotor, so you don’t get V drops... and-or use
slightly higher voltage to compensate..which is a lot
easier than big ga wire. Another 5 Volts will usually do the trick. A 200’
long rotor cable forms a 400’ loop. Why
they don’t just use 50 vdc is beyond me.
later... Jim VE7RF
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