This is a simple, functional model of a double-acting steam engine. Since PLA can't actually handle steam, it's technically a compressed air engine, but the design is very similar to how real steam engines worked. This model should run either with your lungs or with any regular party balloon, you don't need an air compressor. It also doesn't require any specific hardware, screws, lubricants, or glue. I clocked my engine at 340 RPM using a balloon and 750 RPM using my lungs, but yours may run faster or slower than that depending on how well your prints are filed and assembled.

A video of it functioning can be found here: https://youtu.be/LOnf8li0OwM

Required Tools and Materials

• Clippers
• Sandpaper
• Paperclips
• Tape

Assembly You can find a video of assembly with instructions here: https://youtu.be/KDDj87Au3gc I recommend watching the video before printing because it offers helpful print orientation tips and what does/doesn't require supports.

This engine has a 35mm bore (cylinder diameter) and a 25mm stroke. As a double-acting engine, it has two power strokes per revolution, both forward and backward. This makes it easier to start and keep going. That's basically everything I know about engines, so if anyone more experienced sees things that could be easily improved or has any suggestions to make it more efficient, please let me know in the comments.

Curious about steam engines? This is a pretty cool video I found while researching for this project: https://www.youtube.com/watch?v=Imw8L5p7mOk