[Al Skierkiewicz]

There are many answers to this question. The speed controllers do this very effectively by rapidly turning the supply voltage on and off. The effect is the average current changes. As Ohm's Law is stated above, if the voltage remains constant then adding or subtracting resistance changes the current. If the resistance stays constant, then changing the voltage will change current. Either method can be accomplished with switching (switch resistors in or out, battery cells in or out.) or variable voltage source or resistor. In many of the motors supplied for our use, the resistance of a few feet of wire can be almost equal to the internal resistance of the motor. Whenever the resistance of the wiring equals the internal resistance of the motor, by Ohm's Law only half of the available voltage will be delivered to the motor.