Does anyone make a self-driving car? Mapping and localization are the hottest trends in robotics today. And what's more exciting is they can be both implemented with a low-cost robotics kit like LEGO Mindstorms!

I tried to make a self-driving car, after Google's famous car, but I got stuck on the mechanical side of things. I can't figure out how to build a revolving ultrasonic sensor on top of the robot, in order to do mapping and localization.

Any help is highly appreciated!
It sounds like you want to use the Ultrasonic sensor as a revolving radar dish. This is definitely possible. Note that because of the wire, you probably want the sensor to pan back and forth rather than go around in complete circles. Here's an example of what this could look like:



There are building instructions for this project available here:

http://www.nxtprograms.com/radar/