In article . net,
Michelle P wrote:
B.B. wrote:
http://web2.airmail.net/thegoat4/stuff/gyro/
Anyone know anything about this contraption? I'd like to actually
spin it up just for the hell of it, but I'm afraid I may destroy it.
The tag in the fuzzy photo says:
According to the pictures it looks like a Flux gate. It measures earths
magnetic field. It is old.
Most likely 28 volts DC. Power to the wrong pins will ruin the unit.
Hmm ... I've got two old Sperry gyrocompass type devices, which
run from 115 VAC 3 phase, 400 Hz, and several of the points which I see
suggest that this one does too.
Granted -- in the aircraft, the 115 V 3ph 400 Hz was generated
by a motor-generator run from 28 VDC, but that was external to the gyro.
The slip-rings in the gimbal bearings are carrying three signals
in, and the triangular pattern of the capacitors (I think) suggests that
this one runs from three phase, too.
Mine, which was designed to run entirely in the instrument
panel, has only a three-pin connector to feed it power. Yours is
designed as a transmitter unit, to feed information to remotely-located
panel indicators.
One of mine is a gyrocompass (the axis of the gyro is
horizontal). The other is an artificial horizon (the axis of the gyro
is vertical).
Both have torque motors surrounding the gimbal bearings, and a
small dome-shaped object with five contacts and conductive liquid in
them (possibly salt water), which feeds a balanced signal to the torque
motors when the dome is pointed straight down (according to gravity).
If it gets off level, it feeds an unbalanced signal to the torque
motors, and forces the gyro to precess until its orientation is correct.
This correction happens in perhaps the first fifteen seconds after
power-up (and you can see the indicators wobbling like mad). After
that, if there is any slow drift, it will correct that, as well. (But
it might get errors introduced during continuous acceleration or
deceleration -- or perhaps even continuous turning.)
Anyway -- I suspect that at least the gyro motor is spun up by
the 115V 3ph, 400 Hz, and I also suspect that there are synchros or
resolvers running from 400 Hz as well, to transmit the information from
the gyro to the remote unit. Let's see -- the gyro motor needs three
pins to power it, and the synchros have normally five pins, two of which
(the excitation voltage) could be shared with two of the three phases to
drive the synchro, requiring only six pins. It may be that the synchro
excitation is separate (as it is normally 26 VAC 400 Hz), or that the
last pin is a control voltage to cage the gyro prior to spinning it
down. In any case, synchros have three wires on the output signals, or
resolvers have four -- so that could also account for the last pin.
You might try tracing the wires back from the slip rings which
take power to the motor to determine which pins they are. I would
*guess* (but please test) that they are pins A, B, and C (or 1, 2, and
3, if the connector uses numbered pins.) The rest of the pins don't
matter if all you want to is to spin it up. However, you may need them
if you want to feed the signal to a display.
Note that some VFDs (including my larger Mitsubishi ones) can be
convinced to produce 400 Hz -- and can be convinced to back the voltage
down to 115 VAC. Unfortunately, the most appropriate one, my 1/8 HP
one, won't go that high in frequency. Obviously, the VFD is not what
you want if you intend to mount this in your car or boat -- as the 220
VAC 60 Hz power cord would get a bit long. :-)
Good Luck,
DoN.
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