[time-nuts] OT - DC-10 gyros

Bill Hawkins bill at iaxs.net
Thu Mar 28 00:16:23 EDT 2013

Crikey - an alternator?

Automotive alternators typically have 6 poles, which delivers
60 Hz at 1200 RPM. You would need to go to 8000 RPM to get 400
Hz, or a bit more than 133 revs per second. That's really
humming along.

When I was younger, and found a tank gyro about 3" in diameter,
it needed 115 VAC 3 phase. I found an electronic 28 VDC to 115
VAC 400 Hz that was single phase. A capacitor to the third phase
wire would spin it up after you started it by hand.

The motor doesn't care if the excitation is sine or square. There
is a bit more heat dissipation from the harmonics in the square
wave, but nothing to worry about in a small motor. If you are a
purist, as many list members are, you could build a six step
inverter to cut down on the harmonics.

To be practical, divide 10 MHz from a GPS disciplined oscillator
(which is necessary to be talking about this in this group),
use a transistor to switch any available DC into a suitable audio
transformer, and resonate it to 400 Hz with some caps.

There was a time when I'd have killed for that kind of souvenir
from a Northwest aircraft, but now I just sit back and read about
it with fading interest.

Bill Hawkins

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