Edge finder

When you put the edge finder in the middle of the table, it moves forward until it finds the table edge (using the ultrasonic sensor). Then it moves in reverse to the center of the table, then it turns randomly, and repeats that two more times. The ultrasonic sensor works by sending out a very hi pitched sound that you can't hear. Then the sensor times how long the sound takes to get to an object in front of it and back.

Here's what the program looks like: