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Electronics => Projects, Designs, and Technical Stuff => Topic started by: georges shed on July 10, 2020, 02:57:54 pm

Title: How to drive this aircraft servo motor?
Post by: georges shed on July 10, 2020, 02:57:54 pm

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.

[attachimg=1]

Thanks!

Title: Re: How to drive this aircraft servo motor?
Post by: Renate on July 10, 2020, 07:04:54 pm

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.

Title: Re: How to drive this aircraft servo motor?
Post by: capt bullshot on July 10, 2020, 08:03:27 pm

Yes, it's kind of a resolver.

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

Title: Re: How to drive this aircraft servo motor?
Post by: madires on July 10, 2020, 08:33:46 pm

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

Title: Re: How to drive this aircraft servo motor?
Post by: Renate on July 11, 2020, 12:02:30 am

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

Title: Re: How to drive this aircraft servo motor?
Post by: georges shed on July 13, 2020, 09:15:55 am

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