Here's the STL files for my recent 3D printed drive-train. I created the pieces in Autodesk Inventor. I also created a mount-adapter for an Arduino mount found here: http://www.thingiverse.com/thing:101985. I only had square nuts, which explains the square holes. I can make a modification for you if you need it, just request it in the comments. If you do not know what type of wheels you want, you can try out my fully printable mecanum wheels here: http://www.thingiverse.com/thing:172204. The instructions are on there, and you can mount them to servo horns with either glue or drilling (really) small holes and screwing them on. I did the latter without an issue.This should be fairly simple, and hopefully it won't give you issues. I printed it on a Makerbot Replicator 1, and the frame took up a rather large part of the bed. I would suggest making sure that it will fit on your bed when you compile the gcode. I printed with 20% infill, 2 extra shells with a raft. I had no issues with splitting or warping. You'll need 2 Brackets, 3 Spans and 2 frames. Attach with screws with a diameter of approximately .125" (I used computer case screws.)