This mission of this Ball Hunter robot is to find the red ball and to grab onto it. You can place both the blue and red balls anywhere near the robot to start with, and the robot will try to find the red ball and grab it, using the ultrasonic and light sensors.
I recently attended an FRC (High School robotics competition) event at UC Davis, where this year's challenge involves robots from Red and Blue teams grabbing onto big balls of their color and carrying them around a track (plus a few other things, see this intro video).
FRC is mostly remote controlled, but there is a short (15 second) semi-autonomous period at the beginning, where you get bonus points if the robot can score any points without being under full remote control. I was struck by how little any of the teams tried to do during this period. Most did nothing and just waited for the remote control portion to start. Perhaps this is due to lack of suitable sensors. I don't know, but in any case I was inspired to develop this Ball Hunter project to demonstrate some simple autonomous behavior along these lines for the NXT. FRC robots typically have a weight limit of around 100 pounds (45 kg). Do you think my little bot has a chance?