Mike,
I might be able to help you. I had several fit and alignment problems with
my rotating MA-770MDP. I spent a frustrating week last year trying to get it
rotate. No matter what I did, the tower would bind during rotation. At one
point, I was an exhausted, grease-covered 44-year-old sitting on the ground
next to the tower with a couple of wrenches in my hands, literally on the
verge of tears. My one-and-a-half year-old daughter had never seen her daddy
in such a state of distress! It turned out that the solutions were simple.
There were several problems, which Bruce at U.S. Tower helped me to resolve.
He was great, but I should point out that all of the problems could have
been avoided through documentation, none of which is supplied with the
tower.
1. It is possible that your rotor plate was shipped upside down. Mine was,
and so was a friend's (maybe they all are.) If the MA-40 is designed the
same way as the MA-770MDP and MA-850MDP, the plate can be flipped either way
simply by removing the bolts holding it to the base vertical member and
turning the whole assembly upside down. Don't assume that just because it
was shipped in a particular orientation that this is correct. Looking from
the side, the plate is "L" shaped. The horizontal portion of the "L" should
be on the bottom, not on the top (i.e., it should look like the letter "L",
not the Greek letter Gamma.) This is also the orientation that gives the
most clearance between the plate and drive shaft.
These plates are custom fabricated for your particular tower and base. They
are welded in a special jig so that the horizontal part of the plate will be
perpendicular to the bottom of the tower and the center of the plate will
align with the center of the tower drive shaft. When the plate is turned
upside down, that relationship doesn't necessarily hold because the vertical
member and the tower may not be exactly perpendicular (see 4 below). If the
plate is upside down, that would explain why the rotator does not align with
the drive shaft.
2. The mounting holes should be correct for Hy-Gain rotors. On mine, there
are three oval slots radiating from a rectangular cutout in the center of
the plate. My Tailtwister's mounting holes line up at the extreme end of the
ovals, and the fit is very tight. There's virtually no room to adjust the
position of the rotor.
3. It wasn't clear from your message whether the plastic connector on the
bottom of your rotator is clearing the rectangular hole in the middle or
not. Does it go through, but just not allow you to adjust the rotor much? In
my case it was worse: U.S. Tower had not gotten the word that Hy-Gain had
modified their rotors to use a large plastic connector on the bottom instead
of the old terminal strip. The plastic connector on mine wouldn't clear the
hole at all. I ended up cutting a small square notch out of one side of the
rectangle. It wasn't too bad doing this with a hacksaw. I think I cut one
side of the notch and drilled a hole so I could turn the hacksaw blade 90
degrees. I think I could have done better with one of those wire hacksaw
blades instead of drilling (which took forever.) In any event, it takes some
elbow grease but isn't too bad. You might check with U.S. Tower to see if
your plate was manufactured before or after they found out (from me) about
the connector last year. If you're not in a big hurry, I'm sure they'd be
happy to cut it for you. Your local machine shop can do it in a couple of
minutes.
4. Make sure the tower is plumb before trying to rotate it. Since the base
vertical member is not necessarily parallel to the tower, you cannot just
plumb the base vertical member. You have to plumb the tower itself while
adjusting the nuts under the base. I did it with a long carpenter's level.
It doesn't matter if the base vertical member is not plumb, as long as the
tower is.
5. Again, if the MA-40 design is like the MA-770MDP and MA-850MDP, you must
know one critically important thing about how this tower rotates. It is
impossible to guarantee that the tower drive shaft will remain perfectly
aligned with the rotator. This is because the tower tube may not be
perfectly round and will wobble in the upper retaining ring bracket, which
also may not be perfectly round. The tower and shaft also tend to wobble a
bit when the wind blows or if the beam is slightly unbalanced. For this
reason, a small (8") section of pipe is used to couple the tower drive shaft
to the rotator. This is sort of a poor-man's U-joint and provides a
semi-flexible coupling. The pipe attaches to the drive shaft with a small
bolt that is slipped through the holes drilled in the pipe and drive shaft.
An aircraft nut is slipped on the other end of the bolt. DO NOT TIGHTEN THE
NUT SO MUCH AS TO PREVENT THE PIPE FROM SWINGING BACK AND FORTH! Just screw
it in enough to keep the pipe from sliding along the bolt. If you
overtighten the nut, the pipe won't move and any misalignment between the
tower and rotor will cause the tower to bind or jam.
6. DO NOT POSITION THE ROTOR JAWS SO FAR UP THE PIPE THAT THE PIPE CANNOT
MOVE! The first time I mounted the rotor, I screwed the nut down tight
(mistake #1) and raised the plate so far that the top of the rotor jaws
rested against the bolt (mistake #2). The pipe was frozen in place. It was
as if the rotor had been attached directly to the drive shaft without the
pipe. The tower bound up terribly.
By the way, due to the height of the Tailtwister, I had to cut a few inches
off the bottom end of the pipe (recommended by U.S. Tower.) Depending on the
height of your rotor, you might be able to lower the plate enough so that
the pipe can be inserted all the way into the jaws while still leaving
enough clearance between the top of the jaws and the end of the drive shaft
(which is slightly below the bolt.) One to three inches or more of clearance
should be enough to allow the pipe to move. If you can't get enough
clearance for the pipe by lowering the plate, you'll have to cut the pipe.
7. I've experimented with a couple of different ways of mounting the rotor:
A) Loosely fit all the parts together to figure out how high to put the
plate. Lower the plate and remove the rotor. Attach the pipe to the drive
shaft, slide the plate into position, make sure the plate is level in both
directions, secure the plate to the base, slide the rotor onto the plate and
secure the rotor to the plate. If the pipe is over the rotor's center of
rotation, clamp the rotor jaws on the pipe and you're done. If not, loosen
the rotor bolts and try to wiggle the rotor around enough to improve the
alignment. If that doesn't work, secure the rotor bolts and try rotating the
tower by hand until you find a position in which the pipe is properly
centered over the rotor. If you do this, remember to change the rotor's
compass direction to match the beam. If that doesn't work, try loosening the
rotor bolts again so that your can both wiggle the rotator and rotate the
tower to find the best fit. Once the pipe and rotor are aligned, secure the
rotor to the plate and clamp the jaws to the pipe (or vise versa if that
works better.)
B) If procedure A doesn't work, here's another way to do it: Remove all
parts, attach the pipe to the drive shaft and attach the rotor jaws to the
pipe, just letting the rotor "hang" from the pipe. Then slide the plate up
to the rotor and screw in the rotor bolts. Then tighten the bolts that hold
the plate to the base, making sure that the plate remains level in both
directions. If you can't keep the plate level and have the base of the
rotator sitting flush on the plate, you may have to shim the rotor with a
washer or two. I didn't have to do that, so I would recommend trying both
procedures several times before resorting to this.
8. If you have the tiltover base, do not overtighten either the hinge bolts
or the small pin bolts that keep the tilt fixture in place. Doing so can
push the thrust bearing against the drive shaft, making the tower bind. The
drive shaft should remain centered in the thrust bearing.
9. Be sure to liberally grease the upper retaining ring. I use plain old
automotive grease and regrease every three months or so. Also, keep the
thrust bearing lubed. There's a grease nipple on the side for this purpose.
So far, I've only done this once a year, but maybe every six months would be
better.
By the way, my situation was complicated by the fact that a manufacturing
error resulted in almost two inches less clearance between the bottom of the
tower and the base plate. One inch was caused by the fact that they had not
compensated for an engineering change in which the vertical member was
pushed through the one-inch base prior to welding instead of being welded to
the top. The other 3/4 inch was probably due to variation in the base stock
delivered to them (and someone didn't measure it.) As a result, I had to cut
about an inch of excess thread off the tops of the base bolts so the rotor
plate could be slid down far enough for my Tailtwister rotor to fit
(recommended by U.S. Tower.) As I recall, I've only got an inch or so of
clearance between the top of the Tailtwister and the end of the drive shaft.
That seems to be enough, but I'd like more. I suspect that it won't be
necessary for you to cut your base bolts for the HAM IV.
Hope this helps. Feel free to e-mail me if you run into more problems or
would like any other help with the MA-40.
73, Dick, WC1M
-----Original Message-----
From: MBecker@aol.com <MBecker@aol.com>
To: towertalk@contesting.com <towertalk@contesting.com>
To: <towertalk@contesting.com>
Date: Friday, October 30, 1998 2:05 PM
Subject: [TowerTalk] MA-40 Rotor Base
>
>Hi all,
>
>I'm having a little trouble with my new MA-40 rotor base getting the rotor
>into alignment. After mounting the rotor on the plate, it doesn't seem to
be
>centered under the drive shaft. Also, the rotor mounting holes on the
plate
>don't seem to be drilled at the best spots. (By the way, I'm using a
HAM-IV)
>The plastic connector under the rotator hits the plate and the rotor cannot
me
>adjusted on the plate.It's a very tight fit. I guess the solution is to
>modify the mounting plate. Any ideas?
>
>Mike
>KT3U
>
>--
>FAQ on WWW: http://www.contesting.com/towertalkfaq.html
>Submissions: towertalk@contesting.com
>Administrative requests: towertalk-REQUEST@contesting.com
>Problems: owner-towertalk@contesting.com
>Search: http://www.contesting.com/km9p/search.htm
>
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|