The answer is add a motor, drive wheel and a perpetual supply of batteries.

Study "Assembly.skp".

Obtain the following parts:

1) Gear Motor - "6VDC 45 RPM Pinky Finger Sized Gear Motor 1" Long x 15/32" x 3/8"" from either amazon.com or directly from http://sciplus.com/p/MICROMOTOR_47952.

2) Single "AA" batter holder - Radio Shack part number 270-0401.

3) "AA" battery.

4) 8 9.5mm (3/8") ball bearings - I found mine at Ace Hardware.

5) Rubber band, 1mm thick by 4mm wide.

Solder the red wire from the battery holder to the gear motor "+" terminal. Solder the black wire from the battery gear holder to the motor "-" terminal.

Print the PLA parts.

Break the hold down disks off the corners of "Base.stl" and "Top.stl".

The drive wheel assembly is similar to a car wheel / tire assembly where "Wheel Motor.stl" is the wheel, and the rubber band is the tire. Start by cutting open the rubber band such that after the cut it is a strip. Place a small dot of thick cyanoacrylate on "Wheel Motor.stl". Press one end of the rubber band onto the dot and hold until it sets. Roll the rubber band smoothly around "Wheel Motor.stl" until it meets the beginning, then cut it to fit. Place another small dot of thick cyanoacrylate on "Wheel Motor.stl" where the end meets the beginning, then press the end in place and hold until until it sets.

Press the drive wheel assembly onto the gear motor shaft.

Place the gear motor assembly and battery holder in "Base.stl".
Test fit "Axle.stl" in "Wheel.stl", making sure the wheel rolls smoothly on the axle. If not, use a 5/32" drill bit (in reverse), file, and/or modeling knife to carefully enlarge the hole in "Wheel.stl" until it does.

Place "Axel.stl" in "Wheel.stl", then press into "Top.stl".

Place battery in the battery holder, then press "Top.stl" onto "Base.stl".
Place ball bearings on the wheel.

If you are interested in additional instructions on how the video was made, feel free to comment.

Enjoy!