At 07:44 PM 1/23/2007, NPAlex@aol.com wrote:
>I can only guess from your comment that you have not had any experience with
>a prop pitch motor used as a rotator. There are several reasons that one
>would use a prop pitch motor.
>One was cost, as surplus motors were available at very reasonable prices.
And, of course, with a lot fewer propellor planes using electrical
adjust (small planes use hydraulics, and so do many large ones),
they're not available in the surplus market.
>They bring some premium now do to limited availability.
Does someone have a typical spec for a prop pitch motor (torque/speed
curve, for instance).
I found a couple references to 1320 ft-lb, and at 1 RPM, that's about 1/4 HP.
I also found a reference that the current was 20A at 12V, which is
240W, or about 1/3 electrical HP, so it's in that ballpark. I
suspect that there's a fair amount of gear train inertia and
friction, so the no-load current isn't a lot different than the
>Another reason was power, or Torque. They can handle very heavy loads.
>Another reason is size and shape. They fit inside relatively small tower
>cross sections, with no projections beyond the tower sides as some
>of the new
>models do. This makes them very ideal for crank-up towers as all is within
>the tower envelope.
It should be noted that you can buy brand new DC motors with
planetary gear sets (or multi stage spur gears) in almost any
configuration you can imagine. They're just not all that
cheap. But, having not ever actually bought a prop pitch motor(I
have been given a few over the years or inherited them), I don't know
what the going price is. I'd guestimate that a DC gearmotor with a
planetary reduction set to, say, 4 RPM would run about $250-$400,
depending on the HP. A 1/40HP RPM gear motor is about $200. A 1/6HP
AC gearmotor from Grainger runs about $380. A DC motor is going to
be about 20-30% more (for a 90VDC version.. maybe 50-60% more for
24VDC, because of the increased copper size for the lower voltage and
That would get you a totally enclosed motor (i.e. it can operate out
in the great outdoors and work with rain/snow/etc.) with standard
NEMA flanges, etc. For what it's worth, it would make hooking it up
a lot easier, because all the shafts, brackets, etc are all standard
sizes. The gear boxes just slide onto the end of the motor shaft and
bolt to the motor housing. The output shaft is usually a standard keyed shaft.
>The electric motors (nom. 24vdc) are held in place with a large castle ring
>nut, spin that off and the motor unplugs for easy maintenance. The gear box
>removal is on a par with most rotator types.
>One of the drawbacks however is direction sensing. That has to be added.
>Historically that was done by use of Selsyn tx/rx coupled to
>the mast. Today
>both M2 and Green Heron Engineering provide controllers with pulse counting
>direction indication.(K7NV design used with GHE, check out his web
>GHE controller has many features and provides ramp up and down which is
>useful with large arrays.
On motors designed for "motion control" applications (which might be
overkill for an antenna), if you're buying new, they often have a
rotary encoder mounted on the back of the motor. It will be a
quadrature encoder (sometimes with an index pulse) with anywhere from
32 to 256 pulses/rev. You can also get an encoder for the output,
but they tend to be expensive (because people want a lot of
pulses/rev for most applications).
>I have had the same prop pitch motor in service for nearly 40 years, trouble
I think one could expect the same from any reasonably sized
industrial gear motor today. As the supply of prop pitch motors
decreases, you'll probably see more antenna rotator designs using
standard commmercial parts. Sort of like the gradual decrease in
Merlin engine availability as they break, wear out, etc. OTOH, with
it getting increasingly hard to put up towers in many places, maybe
the demand for high power rotators will fall exactly in sync with
Just as a question, since I have my Baldor catalog handy, what is the
inside diameter of one of the telescoping tubular towers? (i.e. how
small does the motor have to be?). It might well be that a standard
56C frame motor won't fit, which does make the motor/gearbox
selection a bit trickier. There are skinny motors made (for use in
well pumps, typically) for such applications. Franklin Electric is
>summarizing - Power (torque) and Size.
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