What will K7NV do when there are no prop pitch motors? I wonder how he got
so many surplus motors? Yes you should be able to make a killer rotator with
parts from Grainger. Telrex had an A/C motor and a separate gear box
connected with a chain. Mine held up much better than the many Hy-Gain
rotators that I owned. I thought about building a rotator similar to the
Telrex with a more modern control box but in the end I went with using prop
pitch rotators. They have an impressive gearbox which seems perfect for
antenna rotating and also holding in position, in comparison most ham
rotators are just toys.
John KK9A
jimlux wrote:
What will the ham world do when the last prop pitch motor dies??
Some years ago I was pricing big DC (and AC) motors with suitable
gearboxes and they are *really* expensive.
The BIGRAK as an example, is 4000 in-lb torque at something like 0.5
RPM, but as noted elsewhere prop-pitch tend to be somewhat higher torque.
The PP has a reduction gear of something like 7000:1 or 9000:1 - so the
basic DC motor is running at 5,000-10,000 RPM or thereabouts. It's
probably something like a 1/3 HP motor (240W @ 24V is 10A...not having
run one myself, I don't know if this is a typical current)
1/3 HP at 1 RPM is about 28,000 inch pounds.
(1700 foot pounds)
Typical AC electric motors have speeds around 1800 RPM, so an 1800:1
reduction is needed. Getting that in one step is unlikely, so figure
you need two gearboxes with 30-40:1 reduction.
So, a $500 3/4HP C-face TEFC electric motor, and a pair of $1000 speed
reducers will set you back about $3000. Plus maybe $500 for a decent
Variable Speed Drive.
At least, you're now using something that is a standard industrial
product and if you need to replace it, you can order the parts anywhere.
Will it fit inside the tower?
A 56C size motor is 6.5" in diameter. I don't think that will fit
inside Rohn 25 (barely).
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