[Al Skierkiewicz]

Everyone so far has neglected the motor power curves showing speed vs voltage vs load vs torque. None of the motors are linear except when no load is connected, so none of the motors connected to speed controllers can be linear. Furthermore, speed controllers apply varying pulse width to vary the average current in the motor not the average voltage. The voltage is always switched between 0 and 12 volts less the voltage drop in the wiring and FETs. The switching frequency also interacts with the segment spacing on the motor commutator and the winding inductance. Although motor manufacturing variations minimize winding inductance variances, they still exist and different motor types have wide variations in inductance, winding resistance and segment lengths. Since motors, speed contollers and drive PWM are never synchronized, neither are motor control outputs, rotations or exact output powers. Light dimmers also vary the pulse width but they synchronize to the power line to reduce RFI and the "singing" of incandescent filaments when power is switched on near the peak of a sine wave. This is often referred to as "zero cross switching".