This is a compressed air engine I made nearly entirely out of corrugated cardboard! You can make one too fairly easily and with few parts!

Please read all directions and look at the pictures before beginning your project!(Maybe even twice!)

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I'm entering this in the Gorilla Glue Cardboard Contest! Please Vote!

See the engine in action here:

Sorry I had a really small air tank to run this off of but the pressures in the video are right, I was able to run this on 5 psi and didn't try anything smaller than that. I would've gone as high on pressure as I could if my tank wasn't an old bottle..

WARNING!: This project involves the use of cardboard and glue! If you have a strange fear of paper cuts(pulpuslaceratapohobia) or gluing your fingers(gluyohrfyngirstohgitherphobia) together this project is not for you!.. Anyway I'm not liable for any strange dangerous thing you decide to do with this information.

Step 1: Stuff You Need

You won't need a whole bunch for this project, here's the list:

Corrugated cardboard (my neighbors had a bunch sitting in their yard)
Old aluminum cans (such as pop, beer, or beverage of choice)
Glue. (I used hot glue and Elmer's Glue-All)
A chunk of steel or other rod (part of a coat hanger could be used)
Scissors
A knife or two
Electrical Tape
A small valve
Patience

This will be fun, let's get started.

Step 2: The Housing

In reality I made my rotor first but that ended up in me redoing it over and over, so you should make your housing first. You can change this depending on the size of the engine you want, but here's what I did.

THE TUBE

Cut some 4"x4" (four inch by four inch) squares out of cardboard. I used 9 for the tube-part, and 2 more for the end panels. That makes 11 total : ).
Find the center of one of the squares and use a tracer to draw a 2 1/4" circle in the middle and cut it out with a knife.
Use the 4"x4" with the circle cut out of it as a tracer for 8 more squares .
Align your 9 squares as straight as you can with the circles aligning and glue them together with Elmer's Glue-all or your preferred gorilla-themed adhesive. I rubber-banded these together to try to get them nice and tight
Hot glue part of an aluminum can to the inside circle of your housing now that the glue is dry.
I chose at the end of this to cover the rest of the housing with aluminum can pieces as well, as it made the housing much stronger. I hot glued them on, then I covered the corners with electrical tape because they were pretty sharp.

END PANELS

Take your two remaining 4"x4" squares and find the center of one with a ruler and poke or drill a hole slightly wider than the rod you plan to use for your rotor.
Use your first end panel you just drilled to mark a hole on your second one in the same spot.
I again chose to cover these with aluminum can chunks.
You don't really need to, but I cut a small hole in one of my panels and hot glued in a small piece of brass tubing as an exhaust. This is just offering a path of least resistance for the air to exit, although it undoubtedly leaks out the sides a little..

- You can try to glue these in place perfectly aligned with each other, but I chose just to rubber band them tightly to the ends of the tube portion of the housing.

AIR DELIVERY

Now you'll need a bit of vinal tubing and your small valve.
Drill a hole the same size as your tubing into the side of your housing. You'll want the hole to come through the side and be arranged close enough to the rotor we haven't made yet to make it spin. You may need to play with this a little bit, but when you like it, hot glue it into place.
Attach your small valve to your input tube you just glued on with more hot glue or a small hose clamp. If you choose to make an air tank for you engine you will attach the end of the small valve to your air tank.

Step 3: The Rotor

After the last long winded step hopefully this one should be a little shorter, but no promises : ).
First you'll need to cut some circles about 1/8" smaller than the internal diameter of your housing. At least that's what worked for me. I used 7 for my nine layer housing. I drew mine on the computer with a combination of GIMP and Paint and printed them out.
Divide the circle into as equal parts as you can, and draw in some fins. Look at the pictures below. You can have as many or as little flaps as you want, I used 8.
Cut out your circles and the flaps. Once you make one you can use it as a tracer like before.
Mark the center and poke or drill a hole through each one.
Align them and glue them together. I used hot glue because I was impatient at this point.
Cut a small piece of steel rod or whatever you decided to use and place it through the center hole on your cardboard finned pack.
Cover the outside of the motor with pieces of aluminum can, which made mine unbelievably stronger and smoother. You can do the sides too if you want to.

Look at the pictures for help : )

Step 4: Putting It All Together

Now you're done for the most part! You're going to put one end cover on your housing where you think the middle is. Put your rotor into the housing. Top it off with the other end cover. Open your valve, blow into it and watch it go or make an air tank!
This is only the beginning for this project. Scale it up, and put it on a skateboard or bike! Play with different rotors with different numbers of fins! Or try a Tesla-inspired turbine! Turn a small electric motor and charge your cell phone! Engines make possibilities endless!