Single Cylinder Air Engine runs on compressed air, a vacuum cleaner, a balloon, or even lung power. I've included three adapters in the design to interface with each.

The design incorporates two ports, one upper and one lower.  When Single Cylinder Air Engine is viewed from the port side, "Wheel Piston.stl" rotates clockwise when pressure is applied to the upper port, and counter clockwise when a vacuum is applied to the upper port.  As pressure or vacuum is applied to the upper port, the lower port functions as an exhaust (when pressure is applied) or an intake (when vacuum is applied).  The opposite occurs when the lower port is used for pressure or vacuum. 

Video of prototype on balloon power is here:

Video of prototype on vacuum cleaner power in slow motion is here:

I probably forgot a file or two or something, so if you have any questions, please feel free to ask.

Designed using Fusion 360, sliced using Cura 2.3.1, and printed in PLA on an Ultimaker 3 Extended.

Printing and Assembly Tips:

Printed on an Ultimaker 3 Extended at .1mm resolution, with 50% infill. Supports are required for "Base.stl". Do not use supports for "Cylinder 484mm.stl" as internal valve body paths cannot be cleaned once printed.

Prior to assembly, test fit and trim, file, sand, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on the colors you chose and your printer settings, more or less trimming, filing and/or sanding may be required.

Carefully file all edges that contacted the build plate to make absolutely sure that all build plate "ooze" is removed and that all edges are smooth. I used a flat jewelers file and plenty of patience.

Study "Assembly.stl" and "Assembly Exploded.stl", carefully noting the locations and positions of the various components as assembly proceeds.

I assembled the Single Cylinder Air Engine in the following order:

1) Slide "Rod Piston.stl" into position in "Base.stl".

2) Press "Piston 484mm.stl" onto "Rod Piston.stl", exactly 38mm from the free end. This must be a very tight fit.

3) Slide "Valve.stl" into "Cylinder Piston 484mm.stl".

4) Press the cylinder assembly into "Base.stl". At this time, the piston rod and valve should easily slide in and out of the "Cylinder Piston 484mm.stl". If not, it's filing time again. Do not overfill as the holes for "Rod Piston.stl" and "Valve.stl" must not be too large in order to minimize air leakage.

5) Position "Wheel Piston.stl" into "Base.stl".

6) Press "Wheel Valve.stl" into "Wheel Piston.stl", carefully noting the relative positioning of the holes in each for "Pin Wheel.stl".

7) Position "Arm Piston.stl" around "Rod Piston.stl", then press "Pin Arm Piston.stl" into the hole in "Rod Piston.stl".

8) Position "Arm Valve.stl" around "Valve.stl", then press "Pin Arm Valve.stl" into the hole in "Valve.stl".

9) Pivot "Arm Piston.stl" into position over the hole in "Wheel Piston.stl", then press one of "Pin Wheel.stl" into position.

10) Pivot "Arm Valve.stl" into position over the hole in "Wheel Valve.stl", then press the remaining "Pin Wheel.stl" into position.

Once completely assembled, I used the vacuum attachment connected to the lower port and a small shop vacuum to break in the engine.  Depending on how well the parts are sanded/filed/trimmed, break in can take anywhere from a few minutes to an hour.

I hope you like it!