Think I first saw this on reddit here. Thought it was a good concept so did some more digging.
Found v1 engineering after like 5 minutes on Google, cool crew pumping out CNC-adjacent open source projects, since dragging a ball across a sand pile is functionally the same thing as CNC/3dp/CoreXY, plus without a z axis they probably had a pretty clear path.
Pretty straight forward setup, 3 rails, 2 of which are being traveled by the 3d printed trucks via toothed belt which is fed through (2) cross corner motors. Middle arm can move up/down, left/right via motors going CW/CCW combinations. Middle arm then has magent which drags metal ball across the sand (baking soda)
Picture of the metal rods I had to cary 3 miles back from home depot because I didn’t have a working car at the time lol
Ball carrying system with ball seen in middle
Pic showing how three arms are mounted to bottom of table
