Operation of a 2 phase servo motorin flight control surfaces
Question
How does a two phase AC servo work?

Answer
Part A - What is a two phase AC Servo Motor?



Part B - How the two phase AC servo motor works
AC Servo Motor - Machine Design



AC servomotors are used in ac servomechanisms and computers which require rapid and accurate response characteristics.
To obtain these characteristics, servomotors have small-diameter high-resistance rotors. The small diameter provides low inertia for fast starts, stops, and reversals, while the high resistance provides a nearly linear speed-torque relationship for accurate control.
Servomotors are wound with two phases physically at right angles or in space quadrature. A fixed or reference winding is excited from a fixed voltage source, while the control winding is excited by an adjustable or variable control voltage, usually from a servoamplifier.
The windings are usually designed with the same voltage-turns ratio, so that power inputs at maximum fixed-phase excitation and at maximum control-phase signal are in balance.
In an ideal servomotor, torque at any speed is directly proportional to control-winding voltage. In practice, however, this relationship exists only at zero speed because of the inherent inability of an induction motor to respond to voltage input changes under conditions of light load.
The inherent damping of servomotors decreases as ratings increase, and the motors have a reasonable efficiency at the sacrifice of speed-torque linearity.
Most larger motors have integral auxiliary blowers to maintain temperatures within safe operating ranges.
Servomotors are available in power ratings from less than 1 to 750 W, in sizes ranging from 0.5 to 7-in. OD.
Most designs are available with modular or built-in gearheads.

Part C - Locking Down Weekend EE Project Suggestion 1/2
I once converted a toy unipolar step motor into to bipolar.  Basically what I did was to tear down the stepper, cut something and get two disconnected coils.  Then I used DC pulse to drive the motor.
Now I have a weekend project suggestion: Instead of using DC signal, perhaps I can use low AC voltage, perhaps from a 200VAC transformer stepping down to 6VAC to drive the two winding 28BYJ-48, treating it as a two phase AC servo.

Warning: I am just a friendly hobbyist. No guarantee no nothing won't melt down or blow up. :)

Part D - Locking Down Weekend EE Project Suggestion 2/2
AliExpress 12VAC 30rpm 4W Induction motor - US$3
Induction Motor Picture - RpiSE 2018jul
12V AC Induction Motor Video - tlfong01 2018jul22

Converting 28BYJ-48 to 6VAC two phase severo motor is a bit tricky, especially if you have not used stepper motor before.  An easier project is to start with a 12V AC inductor motor.  After you have played with the cheapy US$3 AC induction motor, you might like to try you luck tearing down the motor, see if it is possible to separate the single coils into two. Yes, I tore down the motor and found it boringly simple, just a coil and no nothing.
You might like to read the above references to get to know those cheapy AC motors catalog, and how I played with one.





References
(1) Servo Motor Basics - CircuitGlobe
(2) Two Phase AC Servo Motor - CircuitGlobe
(3) Controlling Converted 28BYJ48 Bipolar Motor - RpiSE 2019apr27
(4) AliExpress 12VAC 30rpm 4W Induction motor - US$3
(5) Induction Motor Picture - RpiSE 2018jul
(6) 12V AC Induction Motor Video - tlfong01 2018jul22
(7) Two Phase AC Servomotor - eeeguide 2014
(8) Two-phase A-C servo motor operation - IEEE 1952oct
(9) AliBaba Nema34 CNC Stepper Motor - US$70
(10) AliBaba 1500W AC Servo Moto Price 80b2 1500w 2.4nm 20A Driver - US$275