Example as ball machine: https://www.youtube.com/watch?v=3njcoDqyo1k
Examples as a ball lift: https://www.youtube.com/watch?v=dET0RMmQSZs
Step 1: Design
Unless you're making a circle shape, it's best to use an octagon shape while following a square scaffold.
When making the octagon shape, try making all edges the same size. It's not essential, but it helps later.
Also decide how wide you want it.
Choose some elements which can be used from any angle, such as the path drop, a Ferris wheel, or an arm drop.
Also make sure you consider that the ball machine will constantly rotate faster or slower than you want it to.
Step 2: Returning Ball to Top
Step 3: Stand
Step 4: Counterweights and Gears
Step 5: Entrance and Exit tracks
This is the same as the wheel lift with holes. Just make a hole for an entrance track, or a section tilted to the side for an exit track.
The idea can also be used to change the side of the revolving part if it is wide.