Materials : Cardboard, paper clips, glue, tape
This idea was supposed to be a simple one, but in hindsight, I realized that even the simplest of gears are very frustrating to get working when you are creating them from hand. The “gears” are just two egg-shaped prisms that are pierced through by a bent apart paperclip such that by turning the paperclip, you are turning the gears as well.
Next, I just have a cardboard man with cardboard legs that can move vertically up and down (guided by another bent paperclip). I put the man on top of the gears so that by turning the gears, the man’s legs will alternately go up and down as if he was walking.