Powering Blocks
As I was trying to figure out how to illuminate stackable wood blocks, I came up with this gravity-based mechanism for transmission of power between wood blocks. It worked well for transmission between two blocks and a light bulb, but I haven't figured out how reliable it would be if stacked several times. It could suffer from unreliable connections (causing flickering) or a ton of resistance (dim lights).
Since this was transmitting 120V AC, I tried to make things somewhat safe by recessing the contacts and having the top block drop into the recesses. That being said, we'd still have 120V AC exposed to small hands. :/
It's possible that this approach would work with a 12V DC connection. Maybe I'll come back to it. I'm mostly sceptical of the reliability of the connection once these contacts get coated in playa dust.