How to drive this aircraft servo motor?

[georges shed]

Hi all,

I have this collins servo motor out of a radio altimeter, and ideas how it works/ how i can drive it? It seems to have 3 coils, reference and 2 control.



Thanks!

[Renate]

Yeah, it's a selsyn or synchro, for aircraft usually 400 Hz.
It was designed to have the two control windings being feed from a similar device.
The two devices would be powered by  a reference 400 Hz supply.

If you want to make it spin around without another unit you would have to generate 2 sin/cos control phases and one reference phase
or two quadrature control phases and one variable reference phase.

[capt bullshot]

Yes, it's kind of a resolver.

There's some explanation on wikipedia and other websites:
https://en.wikipedia.org/wiki/Resolver_(electrical)
https://www.dynapar.com/technology/encoder_basics/resolvers/

Most explanations you'll find will deal with them as position encoders, outputting electrical signals. Your device just works the other way 'round, you supply the electrical signals and the shaft rotates accordingly.

More commonly used for this purpose are synchros, most probably you'll find better examples of how to use them as actuators when googling for "Synchro".
Resolvers are 90° shifted two phase, while Synchros are 120° shifted three-phase. Otherwise they work the same way.

[madires]

Synchro/Resolver Conversion Handbook - DDC: https://www.ddc-web.com/documents/synhdbk.pdf
Synchro and Resolver Engineering Handbook - Moog, Inc.: https://www.moog.com/literature/MCG/synchrohbook.pdf

[Renate]

Hey, nobody mentioned the Analog Devices book:
https://www.analog.com/en/education/education-library/synchro-resolver-conversion.html

The DDC handbook looks comprehensive, but they are unfair to absolute encoders for "monotonicity" (pg 3).
I guess that they never heard of Gray code.

[georges shed]

Thanks you all for the reply’s! I’ll look at those links and get stuck in!