My third marble machine is now ready for release. The turning handle adjusts the low point of the circular track and the ball bearing continually rolls down to the low point. By keeping the low point (indicated by the arrow) just ahead of the ball bearing you can make the marble rotate around the track. You can even speed it up so much that you can make the marble fly right off the track.
I didn't previously release the marble roller plans, it was functional but not really working, the gears were a bit crunchy and there was no where easy to hold it. So I took a second shot at it, then a third and finally a fourth shot at the design. Although revamps are easier than the original they're still pretty time consuming, each version gets closer and closer to something that works. (photo of all 4 below)
The final design is a lot more solid because of it's low height. The turning handle became just a stub because it's important for this design to turn with consistent speed. The rotating part gain an arrow to indicate the low point of the disk, the ball will roll fastest if this arrow is kept 90 degrees ahead of the ball. A 2:1 gear ratio seems to fit the rotational speed required. Finally a vertical shaft prevents you from lifting the whole machine off the bench on the up stroke. (svg here)
This kit is available for purchase through my shop http://msraynsford.myshopify.com/products/marble-machine-3