I am a mechanical engineering undergraduate student taking my first course in mechatronics. That gives you and indication of how little I know. I need to control the speed of a DC motor using PWM. What is the easiest (also cheapest) way to convert the PWM output into a power input to the motor? I have read that an H bridge transistor setup is a good way to do this. If so, where can I purchase a complete H bridge?

 

First of all I'll be recommend you to review a block diagram of PWM servo amp for speed control of DC brush motors - see AMC or Elmo products.

Except H-bridge power stage, pay attention on current limiting, speed loop with IR compensation or with speed sensor.