no one will ever use linear drop to control motor speed today period, motor has varying impedance vs load, try giving some push to your motor in the other thread, the speed will screwed up tremendously or load profile will be so poor. everybody is using some sort of smps, buck regulation or PWM nowadays. at most in AC world they use capacitor to shift AC phase to make an AC motor run i'm not aware though linear dropper in AC motor, i'm not the expert. as i said, get a teacher or learn from others/internet how to do it. if you just pop out with some idea, you can waste your time alot. good luck! edit: but at least now you know how to make a good water heater, thats a good thing though while trying and error.
