An instructables on motor controllers for cheap robots by JayWeeks
Almost every robot needs to power a motor of some sort or another. Problem is that motors take quite a lot of power, compared to what most microcontrollers operate with. To solve this problem, robots use what is called a motor controller, which usually amounts to some form of electronic switch that can turn on a very high voltage, using a very low one. That’s what we’ll be making today!
Yup, electricity is quirky that way – you got “very low voltage” (3.3V?), then “very high voltage” (6V?), then “extra low voltage” (<60V), then "low voltage" (1500V)…
Pretty poor circuit (as some people have mentioned in the comments on that original post).