This is part of a kinetic sculpture I designed called Digital Rain (the rest is my gyroid construction set, listed as a "remixed from"). It's best experienced in person, but since it's in my basement for now, a video will have to do: https://youtu.be/fdcw1tt5CR4
Being modular, you can make this as tall as you want (mine is 10 units high, or about four feet). I power it with a 12V gear motor I picked up off eBay that I run at 6V to get about 15 RPM. It only takes a few watts of power. It's pumping about 1,500 5mm steel bearing balls.
This pump and track system requires no glue or fasteners for assembly, it all just fits/snaps together. The track pieces have two little ears to help keep them from curling off the bed; those need to be cut off before assembling. I mounted the motor to the underside of the lid of a wooden box and then used double-sided tape to stick the bottom of the pump to the top of the lid. The drain and collector pieces are tied together through some mosquito netting with a small hole cut in the middle. This is a reliable way to collect balls from a wide area without making a deafening sound.
The main body of the double helix pump was designed to be an attractive and efficient means of lifting a lot of small steel balls. I chose this design because it does not need accurate tolerances: the rotor is significantly smaller than the stator, but the balls act like a bearing and keep everything centered. The track is designed so its own weight keeps the segments locked together, and it forces the balls to flow in single-file which keeps them from getting stuck. The most design iterations were actually around subtleties of the drain and the top of the pump to ensure reliable operation without the balls getting stuck or escaping. I've run this for more than an hour at a time and so far it's holding up well.