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Guard is no more. I splatted the cat, well, the mouse and so Guard was returned to the Lego parts bins, and I've returned to my earlier theme - the attempt to build a four-wheeled robot. Chaser - its provisional name - is another design from David Perdue. There's Ackerman steering at the front, and the rear wheels are independently driven by a motor each. This design, constrained by the parts in the current nxt kit, has the ultrasonic detector attached to the steering motor, so to turn the sensor ...
This is a companion discussion topic for the original entry at https://community.robotshop.com/index.php/robots/show/chaser