Beginner Practical Control System

It depends on what you want to simulate, and why. The problem that you'll find with most control system projects is that you need something to control, and that thing usually ends up being fairly expensive. Here's a few suggestions. All but the last are off the top of my head, and worth every minute I've pondered on their feasibility.

Thermal system: Epoxy a resistor to a small block of aluminum, and epoxy a 3-lead temperature sensor a small distance away. You should get the characteristic slow rise/interesting delay phenomenon, at the cost of a couple of components and a few drops of glue.

Motion control system: Go to a hobby shop and buy the biggest, cheapest R/C servo that money can buy. Take the circuit board out and throw it away. Now you have a motor, a geartrain, and a sensor, all nicely mechanically integrated.

Inverted pendulum: There's a little toy car on the market (or was this past Christmas). It has wheels larger than it's body, and a gravity switch so it'll go forward regardless of which side it's lying on. Buy one, take it apart and put in some sort of a vertical sensor -- anything from a pot with a weight to a few mercury tilt switches to an Analog Devices MEMS accelerometer. Now see if you can make it stand on it's head.

Thanks for the suggestions Tim. I appreciate it!

-lpkeys

That toy car is a good idea. Maybe mount a stick on it. This way you get slower dynamics, which is of course easier to control. (simple example: a child has more problems balancing than an adult) Note that also the placement of the sensor is quite important for a good control loop.