I could not find a gear/motor only kit for the Makerbot Botmobile (http://www.thingiverse.com/thing:13827) so I took the original drawing and extracted the 2 gears necessary to complete the drive train. All credits for the model go to the Makerbot crew who originally designed the car.

Both gears need to be printed with external supports.

I used the following settings:
Infill 100%
Layer Height 0.2mm
Number of shells 1
Feedrate 80 mm/s
Travel Feedrate 120 mm/s

As these have 100% infill, I increasing the filament diameter in Print-O-Matic by +0.03mm for leaner print.

I have not yet assembled the car but at a first glance the gears look as they will fit. Stay tuned for more updates............. :-)