I was using stacked F623 bearings for pulleys, but found that the flanges weren't large enough and the belt kept climbing up on them which was starting to wear out the back sides of the belts, so I got some similar size pulleys with larger flanges and installed them today.  Luckily, there was room for the larger flanges in the printed parts of the mechanism and I was able to just drop them in.  Now the belts stay where they are supposed to.

one more test video, increased speed from Mark Rehorst on Vimeo.

Tonight's project- generate more patterns for the 1" ball (in the photos and video) and generate some for a 15 mm ball, too.  I'll try to make a tool to level out the sand.  Tomorrow: testing for speed and acceleration using the new patterns.