UPDATE: We've replaced the battery case and ultrasonic sensor after discovering a few flaws. There is more clearance under the battery case for the soldering points so they don't snag on the rail. And the ultrasonic sensor mount is longer so that it overhangs the battery case making room for the sensor's connectors beneath. This is still being developed and as it is, we will delete old files and replace them with better ones. This is a basic Arduino robot platform that you can print out and use to learn basic programming and robotic skills, or use as a platform for a more practical project. It incorporates a rail system to slide in new parts including a AA (x6) battery pack, an ultrasonic sensor mount, and a breadboard mount, with many more planned for the future. Instead of re-designing the entire robot, just redesign mounts for the rails. Building this robot. 3D Printing: We printed this out on the lowest possible resolution on a MakerBot Replicator 2. We used rafts and supports but would recommend only printing the body with supports and everything else without them in a separate print. If you have the time, of course feel free to use better resolution! You will need 2 9g micro servos converted to continuous rotation. We have a tutorial here ( http://www.makerzoo.co/converting-servos-for-continuous-rotation/ ). You will also need some 3mm bolts and nuts of various lengths. Also, some small rubber bands could be glued into the groove on the main wheels and also the caster wheels. If you prefer, using friction welding on the casters to secure the wheels in place with a piece of filament works better than nuts and bolts which come loose. We only had long 3mm bolts so we used a rotary tool and a cutting wheel to cut them off. PLEASE USE SAFETY GOGGLES WHEN DOING THIS! The main wheels now fit much better than previous versions. All you need is the screws that come with your micro servo to secure the wheel to the servo armature. The battery case and ultrasonic sensor mount need to be redesigned. We put together both and realized the soldering gets in the way when the battery holder slides onto the rail, and there is no way to access the ultrasonic sensor's pins when the batteries are in the case! Keep an eye here for the updates! Read more here: http://www.makerzoo.co/the-making-of-a-robot-kit/