This was originally a school project. We was devided into groups, and was supposed to make a lego mindstorms car that drove around the track. Our group kind of went a bit beyond the task, and it was very fun. We replaced the firmware in the mindstorms box with LeJOS, a Java Virtual Machine.
It steers with the wheel in the front. And the backwheels is on a differential.
The "tail" on the back is an analog speed-o-meter.
The trailer, as you can see in the video, can be tipped. And while it is tipping, it plays a tune :p I mean, it had the ability, so we just had to use it for something :p
We had to use two mindstorm boxes to have enough input and output "ports". We also used a third one as a remote control, just to be geeky. It uses infrared, and is used to start and stop, and to start the tipping of the trailer. The car automatically stops while tipping.
The turning flag is kind of silly, but we had an extra output port :p