Cheapest and easiest way to slow down a motor

[Stu Bloom]

Originally Posted by billbo911

I'd put money (only a couple bucks) on it containing a "chopper circuit". By using an SCR, or pair of SCR's, it will pass as little or as much of the full AC signal as you set the dial to. To understand how it operates really requires a little understanding of electronics and maybe a picture or two, but I'll try to describe it.
At full speed, the circuit allows the full positive and negative cycles of the AC to pass. When you turn down the speed dial, the circuit will only pass a equal portion of the positive and negative cycles.
Say you only want to provide the motor ~50% power, the circuit would pass 4.15 ms of the negative cycle as it approaches 0Vac and 4.15ms of the positive cycle as it moves away from 0Vac. This adds up to 8.3ms per cycle, half of the full 16.6ms normal AC cycle.
I really hope that helps. This again is where "A picture paints a thousand words" really is true.

[DISCLAIMER - MECHANICAL ENGINEER'S POST]

That sounds analogous to the Pulse Width Modulation we currently use (our speed controllers/victors) to control some of the motors on the robot, except that in your description you are "super-imposing" a duty cycle on an AC sine wave.

[/DISCLAIMER]

Am I even close??