Marvin is a wall (and foot) avoiding robot made from printed parts, an Arduino board, an Adafruit.com motor controller board, 2 motors (from Pololu.com), a distance sensor (from Pololu.com) and a battery clip (Radioshack).
Video of the bot in action: http://www.youtube.com/watch?v=PfaEIkYA8fI
The body, wheels and neck are parts designed specifically to fit what we already had on hand (with the addition of the Pololu parts since we lacked matched motors or a distance sensor).
This bot was created as a mini-project of the MSU robotics group. (Midwestern State University, Wichita Falls, TX)
The printed and electronic parts are bolted together with small screws. Just drill a hole slightly smaller than what you have on hand and ABS self-taps nicely. We neglected to add spacers in the MarvinBody part, so we used some pre-made. We will print the spacers as part of the piece, next revision.
The MarvinCode.zip file contains the (very simple) processing code that runs on the Arduino board. It uses DC motors 3 & 4 and the sensor is on analog pin 0.