Sam Barker and Tom 3D printed a functional seesaw-style railway handcar, then hauled it to the Open Sauce event in the US. The entire assembly had to fit inside checked luggage and reassemble in a hotel room, which ruled out standard gauge rail compatibility and kept the footprint small enough to be called fun-sized. It works: two operators pump the beam, the motion converts to wheel rotation, and the cart moves down track.
The design files are on Printables under 'The Pump Cart', model 1818223. As of publication, the bill of materials for bolts and shafts is still incomplete. That gap matters if you want to build one, and it is worth checking back before sourcing hardware.
The mechanical conversion at the core of this build is what earns a closer look. The original article links the full YouTube build video where Barker walks through how the seesaw-to-rotation linkage was designed and printed. The constraint-driven design process, luggage size limits forcing real engineering decisions, is the part worth reading in full.
[READ ORIGINAL →]