This is my brother's and my second car and third robot. It is the first motorized Lego tumbler I've seen. Even though we only used two motors it is still a neat car. I hope this inspires you. Feel free to use some of my ideas and please comment! I will try to answer your questions. For more pictures use this link http://mindstorms.lego.com/nxtlog/ProjectDisplay.aspx?id=0f64b36b-592c-4667-b12a-f2a5047e3bf8
