As part of a university course, Roland van Dierendonck was tasked with creating an interactive robot and came up with the "Artbot" - an Arduino-controlled robot that draws using a marker pen, and changes its behaviour depending on the value returned from a colour sensor. That is, it can react to its own art work (or that of a fellow Artbot) for some interesting results.
Making the robot is quite simple, with an Arduino and motor shield over a small motorised robot chassis, tank or other base. By placing a black boundary around the surface the robots are allowed to operate within, you can keep them where they need to be and not rushing off to draw on the floor! You can see a pair of Artbots in action through the following video:
If you're looking into starting with Arduino and robotics, such as controlling two DC motors (or a stepper motor) from your Arduino or compatible, check out our HBRIDGE: DC/stepper motor shield. Based around the powerful Allegro A4954 H-bridge driver IC you can control two DC motors with complete ease, or one bipolar stepper motor. With connections for external power management, a complete beginners' guide and documentation - motor control couldn't be any easier. For more information and to order, visit the HBRIDGE: page.