There was too much belt wear at the corner pulleys due to the twist in the belts, and where the belts contacted each other at the twists, so yesterday I converted the mechanism to stacked belts.  I also installed some LED strips with 60 5050 LEDs per meter.  I'll be updating the CAD files with new details.  

The new lighting uses red and blue 12V LED strips with buck converters to drive them from the 24V power supply.  I can adjust the voltages on the converters to control the relative brightness of the lights.  The LED strips are mounted on pieces of aluminum L stock to act as heatsinks and make it impossible to see the LEDs directly.  The way it is lighting the table is exactly how I wanted it to look.

I recently made a tool to level the sand - just a piece of wood with screws near the ends.  I push the tools down until the heads of the screws are contacting the plywood, then just pull it across the table to level the sand.  I've done some experiments with the depth of the sand and it seems like having 1/3 or less than the ball diameter seems to work well and guarantees that the ball won't get stuck.

The video doesn't have the contrast that the table has when you looking at it- the shadows are much darker so the red and blue really stand out.

The mechanism seems to be finished from Mark Rehorst on Vimeo.