There are hundreds of different ways to make robots move, but computer security expert Michal Zalewski didn't see one that did what he wanted: namely, a wheeled robot that could execute sharp turns without complex and expensive design elements like large numbers of independent motors. In response, he planned and built the Omnibot, a three-motor robot whose four wheels operate almost independently, allowing it to perform 360-degree turns and move quickly in any direction.
The robot, which is still in progress, is being made from hand-cast parts plus the motors and sensors. Two diagonally-opposed wheels are controlled by separate motors while the other two turn freely, correcting drift. A third motor operates a central link that synchronizes the four wheels. Using this setup, the wheels can quickly rotate to point forward, sidewise, or diagonal relative to the robot's body. So far, the parts have been cast and assembled, but it looks like Zalewski is still working on getting it to move. You can track his progress at the source link below or see pictures of the 'bot on Flickr.