i made this little guy last semester, but recently re - rigged him because I wanted to learn how to do a facial rig. all the facial articulation is bone - driven, there are no blend shapes on him right now.
the wheel rotation on this automated piston system is accurate to a user defined speed in MPH. all motion is derivative of the middle wheel's rotation. modeled in maya, rigged in houdini, with driving expressions done in python.