SO I forgot that not everybody knows how a 3D Printer works...to be honest...my knowledge is limited. I'll tell ya a little more.
So what happens is someone designs something on SolidWorks (I think it can be other 3D drawing programs as well) and then when you send the final project to the printer magic happens. Really it takes about 15 hours and it actually makes the design...I like to compare the material to plastic, Zach says it's like a honeycomb compound. When the car was designed, Zach and his classmates left space to insert axles and attach wheels, much like a pine wood derby car.
hope this clarifies the mystic world of machinery!