Before we went to Chicago Tardis, I upgraded Mini-Me from being essentially a stationary Dalek to a moving Dalek.
Previous attempts had caused the Dalek to whiz down the driveway going too fast.  Then after about using it 5-6 times on carpet I heard the dreaded stripping of gears sound. The gears stripped because I tried to use a toy car and then a toy tank. Neither did very well (The tank took about 10 uses before the gears started to strip). So I upgraded to a Vex system.

My first attempt looked like this.

Basically I had a Vex kit that I purchased quite a while ago when Radio Shack were getting out of selling Vex products.

I had the thing sitting around for the longest time waiting for the right project.
I had bought a starter kit and it came with a whole pile of metal bits, some motors and wheels. I started building the suggested base project. I made some modifications, added a battery holder and made a slight shape change to fit the pointy aspect of the Dalek innards and to hold the micro-controller receiver.

I realized that really I could not program this kit as it was a starter kit. Even though they gave you a micro-controller unit they did not give you the disk or cables to actually program it, those cost $$$$. So the only things it can do is use bumper switches to stop when it hits an obstacle. But it did come with a pretty decent remote control.

The upgrade in my opinion actually worked out really quite well.
If I were doing it again I would have made him move along just slightly faster, but I think it was pretty good upgrade.