Excerpt from the description in the REPCONN headquarters museum:
"Some folks have asked - why not a protectron with wheels? RobCo wasn't afraid to answer that question: The Protect-O-Bot is the answer. While safety standards prevented this free-wheeling dynamo from entering mass market production despite RobCo's best intentions and teams of lawyers, we take the consolation in letting you see this extremely well-funded experiment as it was intended - a robot moving so fast it looks like it's standing still!
It's a protectron with a car-type design, with wheels rather than normal legs, and a dynamo accelerator. It looks a lot like the torso and head of a regular protectron, with the wheels and legs of a sentry bot, though laying down instead of being upright. The primary weapon, a laser, is mounted at the front of the vehicle, where the protectron's 'head' is located.