zoomkat:
Google any youtube are your friends. Doing some searching you should be able to find examples of code and components you described.
Thanks zoomkat. I was certain that I'd done my research, but your suggestion brought a very interesting link to my attention: MURtle Drawing Robot.
Robin2:
As @groundfungus has said, stepper motors should provide the motion and the position-keeping all in one. I think you will need to use narrow hard wheels with very thing tires to minimize slip between the wheels and the surface.Don't bother with the complication of encoders until you are sure that you need them - i.e. after you have a project that works reasonably well but "could do better".
Ok, I might start off without encoders. But the project above (MURtle Drawing Robot) seems to use IR sensors as encoders. Can anybody confirm this?
Robin2:
MOST IMPORTANT the motors (whatever sort you choose) and servo need to be powered separately from the Arduino. The Arduino can't provide enough current for motors.
Could you elaborate how to do this? So far all I have done is hooking things up to the Arduino. Do I buy a special motor or do I need a separate board or other component that takes care of powering the motors?