Balloon Powered Single Cylinder Air Engine Toy Train is a balloon powered toy train engine based on my earlier air engine design (https://www.youmagine.com/designs/single-cylinder-air-engine) and single cylinder air engine rolling chassis design (https://www.youmagine.com/designs/single-cylinder-air-engine-balloon-powered-rolling-chassis). In order to move the increased weight of this design, I added a 4 to 1 (driven to drive) gear reduction. Even with the gear reduction, this vehicle when well tuned can run over 40 feet on a smooth surface, albeit at a much slower speed. My wife laughed yet again so 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: https://www.youtube.com/watch?v=E6xd2aom9Ew Table top closeup video is here: https://www.youtube.com/watch?v=BXeesJTtcik Video of the engine giving an iPhone a ride is here: https://www.youtube.com/watch?v=lmketkrzKHk 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 on line). 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.