Electronic – Precise motor positioning

You probably need a motor-run capacitor to make the AC induction motor work properly. It does say 8uF on the label.

Also, I really, really doubt the first motor is a stepper motor. It states 100V, 50/60 hz. 100V is the Japanese line voltage standard, and I have never seen a stepper motor with a specification in hz.

Edit Ok, the first motor is a 4IK25RGN-A. This is a 1/30th horsepower AC induction motor.

Realistically, neither of these motors are appropriate at all for a servo system. They both look to be fractional HP induction motors.

You can control speed of an AC motor with a variable-frequency drive. However, VFDs (and induction motors in general) do not have much 0 RPM torque, and don't provide control of the actual motor position, just the motor RPM.

Really, you need a brushed servo-motor, or a brushless AC servo-motor (or even stepper motors). All of these use a different mechanism to generate motion then an induction motor, which is actually a rotating transformer.

I have worked on a airplane simulator that also had this problem. We used a stepper motor, which I think is also a good answer for your case.

A stepper works well here since you know it will need to deliver very little torque and therefore can be counted on to not loose absolute position once it has been established. I don't know why you think a stepper motor will be more expensive than any other small motor, but I don't think that's true, especially when adding the cost of position feedback and gearing. One thing you do need with the stepper is add some way to know you are at a fixed position. A opto-interruptor is usually a good solution for that. At startup, you hunt for the known position, then the firmware tracks it after that.

A servo-controlled motor will be more complicated because you need to add position feedback somehow. That could be a pot with two wipers, or more likely, a shaft encoder. The bare ordinary (as apposed to stepper) motor will need to be geared down, so that adds more cost. This just sounds like more trouble to get working and to keep working, and I doubt there will be a cost savings after you consider all the other stuff this method will need beyond the bare motor.