So previously I've tried to make idler and encoder wheels to just have smooth surface but cover it with some friction tape and it did not work - it created tensions where they were not needed and vice versa, provided no traction where it was necessary.

So now I'm going involute gear path, although I suck at it as with CAD generally.

Couple case iterations and one assembly later I have something that reeks with "a weekend project" vibe - wires everywhere, battery being held only with a double sided tape - the stuff we love, in other words.

It does not have buzzer circuit though, I'm still waiting for DC filter capacitors to arrive.
Anyway, here is some bonus gear action!

Now onto breathing some life into this.