This was one of my first Arduino projects, from around 2008. It is a simple rover that uses an ultrasonic sensor to detect obstacles, and two continuous rotation servos to drive. The chassis and body of the rover was made from plexiglass, some scrap aluminum, bolts, and a ping-pong ball. An Arduino board runs the simple obstacle-avoidance code.
Built and programmed by Bob Rudolph.
https://www.rudolphlabs.com/