Here’s something I always wanted to make, and a big reason I got a GF in the first place (since then, I’ve found hundreds more things I can make!)
It’s a machine that rolls balls in different tracks and changes tracks each time. The pattern is called an ABACABA pattern and it’s the same structure as in binary numbers. (Perhaps you can see how the machine is counting from 0 to 127 in binary?)
The balls fall on a xylophone, 8 notes from an A to another A one octave up. It literally plays “ABACABA” (which continues “abacabaDabacabaEabacabaDabacabaF…”)
The lifter took the most work. I’ve made a nice battery pack since I took that video. The motor is a worm-gear high-torque motor that turns 15 rpm runs on 3v. Each gear has 16 slots, so it delivers 16 balls in 4 seconds, or one note every 1/4 second. More or less.