Question: I've got a small shaded pole motor (C-type) that I'm cannibalizing for use in a project, but the current RPM is too high. I don't want to spend the effort to build a micro-controller to run it.

Is there a way to easily change the RPM by making a relative change to the wound coil? For instance, it's currently running at 2750 RPM, it's 80W, 220V and there are 1500 windings on the coil. Without going into serious design formulas and discussions, are there 'rules of thumb' that I can use to change the RPM? For instance, to half the RPM, half the number of windings, double the wire gauge, or something similar. I'm not aiming at a specific target (RPM wise) I just want it slower - somewhere between one third, and a half of the current RPM.

Answer: 
A shaded pole motor is a type of induction motor, just using some neat magnetic tricks to generate a second phase. It runs at slightly below synchronous speed, the slip depends on the torque.

For a simple 2 pole motor, you'd expect it to run at perhaps 90% of 3000 rpm (50 Hz countries), or 3600 rpm (60 Hz). This is what you are seeing.

If you reduce the voltage, with a series inductor or resistor, the motor will produce less power and depending on the load, the speed will drop and the slip increase. However the torque drops very quickly at reduced speeds, so it's unlikely you will get anywhere near as low as 50% of synchronous speed.

I think that removing turns, keeping the voltage constant, will increase the current and make it run slightly faster against the same load.

[This site](http://www.johnsonelectric.com/en/resources-for-engineers/motors/motor-design-considerations/shaded-pole-motors.html) has some diagrams and specifications. The speed when running below rated speed will be very dependent on the torque curve of the load.

So unfortunately you can only reliably reduce the speed of the motor by reducing the AC supply frequency (and voltage) with a variable speed drive.
Those answers are just mumbo-jumbo-babble. Just use a rheostat at 1000 ohms and plenty of amps ratings. Ohmite makes the best. A rheostat varies the current going through the motor. Research it and you'll see that I'm right. Not many people knows that. Laboratory stir plate are made with a shaded pole motor, a switch and a rheostat. That's all. And their speed is variable from 5% to 100%. Be careful, the rheostat gets hot. It's supposed to do that. That's why the windings are made of nichrome wire wrapped around a ceramic core. Good luck.