It appears that I may have started this thread with my response to "Why a
prop pitch" I guess I need to make additional comment.
Maybe standard components as has been described in the other emails will do
the job, but that would still have to be evaluated.
pitch assemblies modified for rotator service have a pretty good history of
solid performance. They do require some maintenance and K7NV's web site
(_www.k7nv.com/)_ (http://www.k7nv.com/))
goes into considerable detail on what can go wrong, and some detail on
refurbishing, a service he performs.
Prop Pitch motors are still available, but getting more difficult to find. I
just sold one of my spares for $125, and I have seen them range from much
less (flea market deals) to more than double that.
So cost is still one of the benefits.
Size is another - It will slip into a US HD 589 tower completely assembled.
I had to cut one of the upper struts on a TriEx LM 470 to fit it in that 72
ft tower upper section. Rohn 45 and 55 I think are not a problem. Others
have commented the size advantage. It also has a convenient mounting flange
arrangement. At one time TriEx use to offer a Prop Pitch mounting plate.
Connecting the Prop Pitch to your mast is pretty straight forward if you
have the spline coupled Bevel gear with the prop pitch. Again K7NV's site
shows
a few mast clamping arrangements that have been welded to the bevel gear
assembly and provide clamping devices for up to 3" dia. masts.
My solution was a steel shaft welded to the gear, whose diameter resulted in
a slip fit into the heavy walled steel mast. A pair of holes drilled
through the mast and shaft provided a no slip, "pinned" coupling.
Although "pinning" often results in a loose and floppy mast no matter how
tight you try to get the bolts. There is always a difference in diameters
which
results in virtually only two point contact between mast and drive shaft.
This can be overcome by using a proper pinning technique. Using Allen Socket
head bolts instead of conventional Hex head, and enlarging the "entrance" hole
on the MAST to allow the bolt head to engage the drive shaft makes a secure
and reliable coupling that for me has handled multi-band arrays including
full size 40m beams. Note, the "entrance" hole diameter should be a few
thousands over the Socket head diameter for best results. I used two half
inch
bolts.
Finally the problem of direction indication. Selsyns where the standard of
the 50's, 60's and beyond. Required gears, belts or friction wheels to
couple the mast movement to the selsyn shaft. Resolution was poor, and
typically
required 115 vac to be routed up the tower. Oh and don't forget you need
rotation limit switches as well.
There was even "point and turn" schemes using a third selsyn in the shack
readout box.(Bill Orr's Handbook of circa 1950's. But today there are more
elegant solutions that result in reliable and accurate position indication.
Using either reed switch or Field effect transistor and a magnet attached to
the
motor shaft. The motor speed varies, but I think ranges from 6000 to over
9000 rpm. that also is the speed conversion ratio of the planetary gear box
(about 9000 to 1) Lots of torque, and resistance to windmilling.
The Green Heron Engineering controller box seems to offer the best method of
controlling a prop pitch system available today. M2 2800 box does as well,
but has some lesser features. It still is very possible to get the job done
with a good 24 to 30 vdc power supply capable of about 10 to 15 amps, some
relays and switches. The read out could be as ordinary as a potentiometer
coupled to the mast, and conventional milliameter readout in the shack.
I like prop-pitches - note I have a couple of old time Radio
Industries/Hallicrafter Loudenboomer rotators available. Double worm gear,
1/8hp GE motors,
high torque, continuous rotation with coaxial feed through the rotator. See
my web site - _www.w4qn.com_ (http://www.w4qn.com)
Regards,
Norm W4QN
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