I really like the wheels on this robot, it looks like a good solutions for omni directional movement. The maker said it cost about $10 and took about 20 hours to build. Unfortunately there aren’t any schematics posted yet. Check out the link for more information.
This is not a very intelligent, or special robot – it took me long enough, but it was really just for my education etc. This is about 10cm high, it is a clear ball with three servo motors, driven by three 74AC740 ICs. The ICs measure the amount of light coming through an array of sensors on the top, and rotate the balls in a direction and speed proportionally to that. The result is that the ball “drifts” towards the brightest object, or follows a spotlight directed down at it.
More about this Three wheeled light seeking robot