Summary

This is for a low price opensource Arduino robot with room for a breadboard, micro servo and sensors.

This is a very old version of the robot chassis. The latest version can be found at http://www.thingiverse.com/thing:273520

The newest version removes a lot of unnecessary parts and is just a better design.

Instructions

---------------- Parts List --------------
2 x Continuous Rotation Micro Servos (http://www.robotshop.com/en/9g-continuous-rotation-micro-servo.html)

From Adafruit:
Trinket mini chip - 3.3v or 5V (http://www.adafruit.com/category/167)
4 x AA Battery Holder (http://www.adafruit.com/products/830)

Other:
Jumper wires
2 x small Zip-ties

---------------- Optional Parts List --------------
Reflectance Sensor (http://www.pololu.com/catalog/product/2459)
Additional Ball Caster if the bot will be front heavy.
Micro servo (http://www.adafruit.com/products/169)
Motor Driver (http://www.adafruit.com/products/807)
Upgraded micro controller.