4WD Buggy

I saw a video on youtube of a four wheel drive buggy, and I like the design.  I tried to build my own version, using 2 medium motors in the back and two large motors in the front.  Unfortunately, I had no great off-road wheels, so I used other ones that aren't as good as I would have liked.  Here is the video I watched: http://www.youtube.com/watch?v=uff7vZ-Pcds

Here is the robot, with the "protection" I added to it:

This is the robot without the outer layer.  If you look carefully, there is a turntable gear in behind the front motors; this is to allow the front wheels to rotate from the back wheels, so when it goes over an object only one wheel will go into the air and the rest will remain pushing on the ground:

Here is the robot in action: