This track runs best with 2 "marbles" using the recommended power supply set at 4.5 vdc with the recommended motor in the instructions. I'm studying different approaches to track design, and this was an interesting intermediate step, to me at least, as I did like the repetitive sound it made. I printed this prototype track at high speed thus it appears rough, but it works. As can be seen at this print speed, a little sanding and filing is required to clean it up if you print yours at this speed.
Designed using Sketchup Make 2015, and printed in PLA on a Makerbot Replicator 2 using Makerware 184.108.40.206 "Standard" Settings (.2mm layer height, 2 shells, 10% infill) at 200% print speed (only because it was late and I was tired).