This instructable will show steps for creating a Hero's Engine. Also known as an Aeolipile, which translates to the Ball of Aeolus (the Greek god of wind), the device consists of a chamber that rotates due to thrust produced by tipjets. In my version of the Engine, I used a rounded steel chamber with two curved copper tubes as the tipjets. When the chamber is heated, the substance in the chamber (usually water) is converted to vapor, which then exits the vessel via the copper tubes, producing thrust and therefore the trademark rotational motion of the engine.

Please let me know if there are any ways you think I could improve this instructable, and if you have any suggestions for design or constructions modifications.

Shameless Self-Promotion: If you like it, vote for it in the Make it Move contest! Please?

Disclaimer: Multiple instruments are used within the construction of this project that are dangerous if used improperly. Furthermore, if the project is successful and the end result functions correctly, then it will spew hot steam, boiling water, flame, or any number of potentially hazardous substances. Don't hurt yourself, and its not my fault if you do.
Another Disclaimer (New videos=more uses of the engine=more minor injuries=more safety advice): Because of condensation, the method of filling the chamber, overfilling the chamber, the nature of the apparatus, and more, it is possible (read: likely [read: pretty much inevitable]) that you will have some sort of liquid (rather than vapor) discharge from the tubes. In my Engine, the drips from the tubes land right on the hand holding the torch. Although in my experience, this is significantly more likely with the water-filled vs the alcohol-filled Engine, PLEASE take necessary precautions to keep yourself safe. Furthermore, even though the alcohol-filled Engine is less likely to drip, this is by no means a reason to take fewer precautions. The risk from fire not only exists from the rather conspicuous jets of flame from the tubes, but also from the drips which primarily happen at the beginning (before the flame heats the tubes enough to vaporize them before they reach the ends). In short, make sure the area around the Engine is safe, and make sure you protect yourself adequately. One last word of wisdom: don't try to "pre-heat" the tubes with the torch. It's difficult, unnecessary, and if there is any liquid in the tube at all, the tiny amount that you vaporize will eject the rest of the volume of liquid, most likely onto some place where it will cause you pain. Trust me.

More information on Hero's Engine:
http://en.wikipedia.org/wiki/Aeolipile

A video of my Hero's Engine filled with water:

Alcohol-Filled Engine (the real reason you should make one of these)

Step 1: Materials and Equipment

These are the materials and equipment I used. I will try to indicate when other tools/materials would work, but feel free to ask or look at the rest of the instructable if you think something will work and I haven't listed it.
Materials:
1 Sheet 22 gauge steel (12in x 24in)
5 ft of copper tubing (1/8 in) I used cooling tubing originally intended for a refrigerator/air conditioner/something else from Home Depot
Solder
String (I used old kite string I had lying around)

Equipment:
Dremel tool with cutting wheel and small grinder
Ball-peen hammer
Vise (both to hold material and as place to work the metal)
Blowtorch (for sweating [brute force soldering] the connections and for operation of the final product)
Aviation Snips (for cutting the steel: very heavy duty, and ideally not ones you mind getting a little dull)
Bag of something impact absorbent and moveable for shaping the metal on (I used charcoal, but anything like sand, gravel, dirt, etc should work. This will become clearer later)

Step 2: The Chamber Hemispheres

The shaping of the two halves of the chamber was, for me, the most difficult part of the entire process. It requires a lot of patience, and there is a significant learning curve. After I saw that my second one was so much better than my first one, I went back and tried to fix up the first one. It kind of worked. What you are seeking to achieve is two equally sized (especially in diameter, but also, for aesthetics, in depth) hemispheres that protrude from the FLAT metal. This is important because the two sides are soldered together later, and the smaller your gaps are the less irritating that step will be. Anyhow, on to the step by step part:

First, if necessary, cut your steel until you have two 12x12in squares (this is a little large, but personally, I needed the room to work with).
On your bag of charcoal (or sand, or dirt, or gravel, or whatever), place on metal sheet. Find (roughly) the center, and hit it with the ball end of the hammer.
Work in generally concentric circles, continuing hitting the metal until you have an indention that is slightly smaller than how large you want your chamber to be. IMPORTANT: your chamber can only be as large as the largest distance your vise can open.
Open your vise to the diameter that you want your chamber to be, place the indention within the vise, and begin to hit it with the hammer again. Work in one area, slowly rotating the piece, so that you end up with a perfect circle.
Repeat for the second hemisphere
Optional (but HIGHLY recommended): at this point, trim the excess metal from your hemispheres. I used old, super heavy duty aviation snips, and left about 3/4 of an inch of metal. However, I did this AFTER soldering the tubes into it, which made it more difficult than it needed to be. Another note about aviation snips: they exert torque when they cut, which, in mine, led to warping of the metal. I had to go back to the vise and hammer it flat again.

Step 3: The Tubes and Their Placement(or Nozzles, or Tipjets, or Thrusters, Etc)

By the very nature of the engine, there must be tipjets to provide thrust. Unfortunately, this means cutting two (albeit small) holes in one of the chamber hemispheres that is so precious to you. Something to note: you could theoretically finagle the design so that the two tubes came out from the seam between the hemispheres, but that seemed way too hard, and you could also put one hole at the apex of each hemisphere, and have the thrust be perpendicular to the way I did it, but I did not trust that the chamber would be balanced and didn't want to deal with the accompanying problems that that caused. Moving on,

First, choose which hemisphere you like more (which is prettier). Then, drive a nail through it twice, (ironic, I know) making two holes that are close to the rest of the sheet (depthwise, see picture) and across the diameter of the hemisphere from each other.
Using the small grinder on the Dremel, widen each of these punctures until they are the outside diameter of your copper tubing.
Using the cutting wheel on the Dremel, cut two sections of copper tubing of equal length.
These sections will be soldered into the holes you just made. As I said before, I recommend trimming the excess steel off before you put the tubes in. For trimming instructions, see step 2.
Bend the tubes into whatever shape you wish, but be careful about two things:
Do NOT bend the tubes so much that you kink the tube
Make sure that the tubes will provide thrust (torque) around the same axis of rotation, in the same direction

Design Idea from djokimaki: To avoid/attenuate expulsion of hot, dangerous liquids from the tubes, it may be a good idea to have the tubes extend further into the center and then bend toward what will be the top of the chamber (further up into the hemisphere), so that they have a greater propensity to collect vapor rather than vapor and water. However, due to condensation, this will probably not completely solve the problem, so please take steps to protect yourself. Also, don't try to preheat the tubes, because its difficult, fairly dangerous, not worth it, and chances are that you'll melt the solder connections between the tubes and the chamber and just feel stupid (like I did)

Step 4: Sweating (soldering) the Engine Together

First, sweat the tubes into the holes in the chamber you made holes in (fairly obvious there)
I will give a quick explanation, but for more in depth analysis of the process, I encourage you to look at this wonderful instructable . The general idea of sweating is to use something (a torch) to heat the living daylights out of a piece (or two) of metal, and then squish solder into it, which immediately melts and seals the joint. So:
Stick the tubes into the holes in the chamber. It should be a snug fit, both because it cuts down on unnecessary solder, and because if you're like me, you got really sick of grinding the holes and made them as small as they could be and still work.
Using the torch, begin to heat the area where the two metals join. Two tips here: while possible to do with a pair of pliers, I much preferred using the vise to hold the work at this point. Also, I soldered the connections from the inside, mainly for reasons of vanity and wanting it to look pretty at the end.
After the area is screaming hot, squish solder into it until there is a fully sealed connection.
Repeat for other tube.

Sweating the two chamber hemispheres together was a pain. Two main things to shoot for are a flat, gapless interface between the two sides. Also, keep the work level at this point, so the solder doesn't just leak out the bottom when it melts.
Same procedure as above, but with a much larger area. Another tip: torch the work from the side that does NOT have your tubes in it, so that you don't melt the solder holding your tubes and create the need for a repair.

Step 5: Design Recommendations and Other Musings

Design recommendations:
Now, although you theoretically have a functional engine, it works much better suspended from a string. I took some of my leftover copper tubing, cut it into about a 16inch section, cut a notch in each end, and squished it around the edges of my engine, then tied the string to that.

Musings:
One thing I did after the novelty of steam wore of was I filled mine with alcohol, just for fun. Although great fun, it requires constant application of the torch to continue to vaporize the alcohol. My as yet untested idea is to bend the jets to the point at which they blow fire onto the bottom of the chamber, allowing the Engine to perpetuate itself.

Please let me know if you have any other modifications, questions, ideas, comments, concerns, worries, cares, or really anything relating to this project. Or relating to a related project. Et cetera.

Also, I will try to get a video of the flaming, alcohol filled Hero's Engine up as soon as possible.