Here is a little robot the kids and I were working on.

We designed it in Solidworks.

Prepared for printing in the MakerWare software.

Printed it on the MakerBot.  It failed halfway through and we had to re-print some of the parts.

Here is a closeup of the print.

And some pictures of the finished chassis.

We used custom rubber bands for tires. Threads were even printed into some of the parts so 6mm bolts could screw right in.