Parts I purchased:
1) 60RPM Speed Reducer Rectangle Shape N20# Magnetic Mini Geared Motor 6V DC (Amazon, http://www.amazon.com/gp/product/B00AUCGJX0/ref=oh_aui_detailpage_o08_s01?ie=UTF8&psc=1).
2) Coaxial Power Jack (Radio Shack part number 274-1583).
3) 3.0 Vdc Power Supply (Radio Shack part number 273-315 with the "N" style plug 273-345, you get one free with the power supply).
4) 14 or so "marbles" (8mm ball bearings purchased at a local Ace hardware store, also available on Amazon). You can use just one if you so desire, but 14 makes sure there are marbles on the track at all times if you want to run the motor at 6vdc.
5) Large rubber sticky feet (available at hardware and dollar stores).
Print all pieces as shown in "Assembly.skp". Carefully remove the hold down pad on "Star.stl". If anyone has warping problems printing "Track.stl" (I've printed 6 without warping problems but I carefully trammeled the build plate with a feeler gauge before each print) I can add hold downs if required.
Test fit and trim, file, sand, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on the colors you chose and your printer settings, more or less trimming, filing and/or sanding will be required. After assembly of the three screw pieces, I used the completed assembly as a "ream" of sorts to clean out the larger tube on "Track.stl". I also used a #2 pencil to clean out any tiny filament strings on the track surface of "Track.stl". By carefully cleaning the track, marble entry and exit points, and spine tubes will make sure your assembly operates properly.
Assemble as per "Assembly.skp".
Wiring is pretty straight forward and simple, however you'll need minimal soldering skills and soldering equipment. Basically, solder a 3" red wire between the gear motor "plus" terminal and the coaxial power jack "Center" terminal, then solder a 3" black wire between the gear motor "minus" terminal and the coaxial power jack "Shield" terminal.
Comment if questions.
Hope you like it, and Merry Christmas!!