Balloon Powered Single Cylinder Air Engine Toy Train is a balloon powered toy train engine. This vehicle when well tuned can run over 40 feet on a smooth surface, albeit at a slow speed.
My wife laughed hard when this toy train engine chugged through the kitchen and into the family room that, well, now there's now quite a few more of them (this time she liked the colors I chose). And yes, it still sounds like a steam engine.
Distance test video is here:
iPhone on a train ride here:
Tabletop closeup video is here:
You will need to purchase 4 "AS568" #219 o-rings (1 5/16" I.D., 1 9/16" O.D, 1/8" section) for the tires and at least 1 "punch balloon" (I found mine at a local party supply store, but they also are available online).
I probably forgot a file or two or something, so if you have any questions, please feel free to ask.
Designed using Autodesk Fusion 360, sliced using Cura 2.3.1, and printed in PLA on an Ultimaker 2+ Extended and an Ultimaker 3 Extended.