[Top] [All Lists]

[TowerTalk] HAM IV rotor / mast slipping / Slipp-Nott

To: <>
Subject: [TowerTalk] HAM IV rotor / mast slipping / Slipp-Nott
From: "Jim Thomson" <>
Date: Fri, 6 Apr 2012 07:07:55 -0700
List-post: <">>
Date: Thu, 05 Apr 2012 21:41:20 -0500
From: John Becker <>
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 

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


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 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 

##  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      


TowerTalk mailing list
<Prev in Thread] Current Thread [Next in Thread>