This is a classic physics gravity well demonstration. It uses about forty 6mm diameter plastic Airsoft BBs that get pumped up to the top of the funnel and spit out tangentially. It prints in 3 pieces without supports.

Note that at the output end of the feed tube, there is a cantilever arm with a little bump on the end as shown below:

You will need to use an Xacto knife or other small blade to free up the little cantilever arm after printing. The little bump at the end of the cantilever impedes the balls slightly, forcing them to shoot out with a higher velocity into the funnel.

Next, make sure that your BBs run smoothly through both the funnel and the feed tube. Remove any nits that may be blocking the path.

The back plate with the center post should snap into the main body. You will probably want to secure it with a couple of drops of superglue. Then just slide the drive disc over the center post. Drop your balls, a few at a time, into the funnel and work the disc back & forth to get the balls distributed around the disc. Note that the fit of the disc is tighter towards the feed tube (pinching the balls) and slightly looser towards the funnel side. At this point, you should be able to turn the disc and feed balls up into the funnel.