Here is a small project a friend and I worked on using the Lego mindstorms NXT.  Essentially, the robot detects if any physical object has pushed against a touch sensor. If so, then the robot clamps onto the object and attempts to move it.

We programmed the sensors and intelligence onto the brick using leJOS.

This project is from 2007. (11th or 12th grade) Enjoy the ancient video…

– csTom