9.3 Are we done?

Since most controllers can general PWM waveforms, shouldn't we be done?

Unfortunately, DC motors require feedback for precise control. What we have discussed up to this point is merely ``throttling''. You cannot drive a car blind-folded with just a gas pedal and a brake pedal! Similarly, just being able to PWM a DC motor does not mean we can control the rotational speed. The actual rotational speed of a motor depends on many factors, including internal friction (it changes over time), terrain, battery output voltage (also changes over time), switch efficiency and many other factors.

In short, we have little idea of how fast a motor is actually rotating!