Introduction: The Stirling Engine, Absorb Energy From Candles, Coffee, and More!

There's energy all around us that's just waiting to be tapped into. Whether it's hot coffee on a cold day, light from the sun, scented candles, waste heat from electronics... there's power to be had! How about we turn it into useful power? Step in the sterling engine.
Ever put a tightly filled balloon in the freezer, then come back and see it largely shrunken? Once you bring it back out into a warm room it expands again. Now what if we could use that expanding and contracting for moving a piston... and you've got the general idea. If you heat the air, it expands, if you cool it it contracts. It's a very simple idea, for a very simple engine.

let's get building!

here' s the video of the build and the engine working!

Step 1: Materials

Required tools:

utility knife
plyers (long nose)
wire cutters
drill bits 1/16, 5/32, 1/2-3/4
drawing compass

CD and case / large plastic jar lid
10x5 inch piece of steel or aluminum two 5x5 pieces are fine, needs to have some thickness
CD tower (or even better) a LARGE 5 inch wide glass bottle. (see picture)
EPOXY (JB weld/ JB kwik AND regular, cheap epoxy. If it says non shrink, don't get it!)
    *there's been a lot of issue with epoxy, I never realized different epoxies would cause such a difference, so I've added a picture of the epoxy. Here's one place to buy it:  Hopefully this clears up the issues!
wire (welding rod is preferred, Stainless steel is best) 1/16 inch stainless or 1/8 steel - MUST BE SMOOTH and straight!
7 inches of PVC pipe
Foam board (5x10 inches or more, two 5x5 pieces are fine)
3/4" copper pipe

hotglue and glue gun
fan weights

Step 2: Cut CD Tower

This step is pretty easy, measure an inch from the top of where you'll make the cut and mark. With the CD case I'd suggest filling it with CD's up to the point where you're making the mark, take it slow, and use that as a guideline for drawing all the way around.

Now, for a really nice pretty cut, I used a drill press and a cut off wheel and was able to make a very level cut just by spinning the case (see pictures) HOWEVER, this isn't needed, a saw will work just fine, that's why you need to make sure you mark level all the way around the case. It helps a LOT. Also, cut the top off last, it'll provide support and make it a LOT easier to cut.

Step 3: Cut Displacer

This is pretty easy, pull out your foam board and compass. Using the top cut from the CD tower, span the compass from the middle to a fourth of an inch from the edge (2.25" to be exact). Draw two circles on the foam board (make sure to mark the middles!) and cut out. I'd suggest cutting the two circles roughly then use a jigsaw or the like to finish the cut smoothly. If you don't have one, the scissors will work fine.

Stack the two circles, then, using matching electrical tape, tape them together around the circumference. If you want you could glue them together, and it's not going to cause a problem.

Step 4: Cut Aluminum

Pull out the CD tower top again, or use your compass and draw two non-overlapping 5 inch circles. Use your hacksaw, take it slow, and slowly round out the circle. It doesn't need to be perfect, and mine wasn't for sure, but it always helps.

Step 5: Drill N' Glue

Here's where problems can creep up if done wrong, they're not critical... just EXTREMELY annoying. Using your small drill bit (the one that matches the rod you're using, in this case 1/16") drill in the CENTER of one of the plates (whichever will be the top plate) Stick the rod through and make sure it's a nice SMOOTH fit. If it doesn't seem to fit do three things:

1- run the bit through the hole again to make sure it's clear
2- file/sand down the edge of the wire to make sure it's not de-formed and causing the problem
3- if it just doesn't fit, try wiggling the plate around a bit to widen the hole.

Once that's fine, cut an inch of either pipe or 1" C stock, or angle stock (I used angle stock) This is because, in order to maintain efficiencies, we need to be as air tight as possible, yet smooth. If you were wiggling the wire around, you may have noticed that it tends to "stick" when at any angle. We need to keep it perpendicular, and that's what we'll do. Anyways, secondly, cut a small square (or circle) of metal from the scraps you cut off while making the plates. Drill a hole in the center of it (as seen in the first picture)

Move the piece of angle stock or whatever so it "centers" around the hole. Glue down with epoxy.

Poke the wire through the hole and the small square, make sure it still slides smoothly, and glue down. As the epoxy cures, periodically check to make sure it still moves freely and adjust if necessary. (if worst comes to worst and the wire "freezes" up, re-drill the top hole with the next sized bit. Avoid if possible)

Finally, near the edge, (see picture 4 & 5 ) drill a 1/2"-3/4" inch hole. As long as the pipe you're using for the cylinder doesn't fall through it, you'll be ok. Make it as big as possible though!

Step 6: Casting and More Gluing

Here's where we cast a piston. I've tried nearly everything under the sun I could find. Nothing. Without machining something, you're left with very FEW options of what to use for a piston. Now, if you don't want to worry about this, you could go to and buy a piston/cylinder (or a dashpot w/ some slight modifications) and use that. They've got excellent machined graphite pistons running in Pyrex tubes...

But, if you're just the average person who doesn't feel like ordering anything, we'll just cast one.

So, break out the epoxy (this is the non-nonshrink stuff)

1- cut around one inch of copper pipe with a hacksaw. (sorry about the pictures, I used a huge piece, I meant to use an inch of pipe)
2- using the utility knife, trim the inside edge of the pipe. DO NOT USE SANDPAPER. this is to smooth it for when we push the cast piston out.
3- clean out the inside of the pipe until it's nice and shiny. Use Windex to help.
4- wrap the base of the piece with plastic film (saran wrap)
5- oil the inside of the pipe, regular spray on cooking oil is fine.
6- warm up your epoxy, we want it nice and runny.
7- mix enough to fill a half inch of the pipe or so.
8- wait
9- once cured, remove the saran wrap and the cast piston should push right out. It may need some force, but it'll come.
10- take some wire (about an inch) and bend the end into a hook like seen in picture nine
11- drill a hole in the piston and glue the wire piece in.

While you're waiting for the piston to cure, pull out the JB weld or kwik and glue the plastic piece of the CD tower you cut to the bottom aluminum plate. This is the one that hasn't been drilled into.

*for more advanced builders* you might want to try using a glass cutter and cutting a pyrex cylinder from a test tube instead of a copper pipe.

***WARNING*** I'd like to note that for the BEST piston results:
1- do not mix the epoxy in the cylinder. The oil seems to contaminate the mix and keep it from hardening. mix on wax paper or saran wrap.
2- Do NOT use 1 minute epoxy. Avoid 5 minute epoxy as well. I tried one minute epoxy and it got really hot in the tube. The problem comes when it cools then severely contracts, leaving TOO much of a gap. It's thermal expansion, plain and simple. This needs to be avoided. Warm should be ok. Hot is not.

Step 7: Bending... Bending... and More Gluing

Here's a KEY part of this project... bent wires

To start, take the wire and bend another hook (get used to it, we'll be doing a bunch of hooks) Go ahead and cut it at about 5 inches. Sand down the end (file, grind, whatever, make sure it fits through the hole in the aluminum plate) Then, pull out the JB kwik and glue the hook closed. Go ahead and do the hook on the piston while you're at it.

1- lay the top plate on top of the bottom piece (which has been already glued) so the small hole overhangs.
2- put the piece of wire through so only the hook is showing on the top side
3- mark with sharpie or permanent marker.
4- cut

Now, onto the other two hooks

1- bend a hook on the piece of wire.
2- measure two inches from the base of the hook and mark.
3- cut at 2.5 inches from the base of the hook.
4- bend at a 90 degree angle at mark
5- bend a bit of the end to keep hooks from sliding off (see pictures)
6- repeat
7- use epoxy and glue the hooks shut as usual.

Step 8: Even More Gluing... and Crankshafts

Cut another section of pipe. (needs to be from the SAME piece of pipe as the piece you used for casting) This piece should be three inches long, clean both inside edges like you did for casting, as well as clean the inside of the pipe VERY well. Center over the large hole you drilled, and epoxy.
Once the epoxy cures, wipe the inside of the pipe with an oiled paper towel. Test the piston. As a note, you'll need to twist the piston until it slides freely. This is because the inside of a copper pipe is EXTRUDED, this means you'll have small ridges that run the length of the pipe, they're smooth and do not inhibit travel. BUT, they need to be matched with your piston which was cast with those ridges. Just move the piston up and down while slowly twisting until it moves freely. Mark the pipe and piston (for ease of matching) and remove piston.

Finally, onto the crankshaft. This is a CRITICAL piece of your engine. It MUST be as straight as possible, and, cannot have cams that are too deep. Doing such will cause the engine to not run.

here's the dimensions you should use for how deep the crankshafts should be. The crankshafts for the piston needs to be .15-.20 inches deep. The displacer needs to be a little less then .25 inches deep. You'll probably not get it right the first time, so don't worry about that, I made two and the second one turned out much nicer then the first. (unfortunately I got pictures mainly of the first) As a note, they can be bent in a trapiziodial shape rather then being rectangles. Also, the two cams need to be 90 degrees out of phase from each other. (if one is sitting flat on the paper, the other should be standing straight up)

1- measure distances of where the two cams need to go (where the rods for the displacer and piston are)
2- mark them down on a sheet of paper for reference
3- Cut a piece of wire 8 inches long
4- make first bend (measure and everything) Use both plyers.
5- roll the wire and make sure it still matches AFTER the bending.
6- make second bend 90 degrees from the other along the length of the wire.
8- roll wire to make sure it's still flat after bending. Bend slightly until it's straight again.

Step 9: More Glue, Some Hacking, and a Side of Drilling

Yes, we're going to be gluing even more.

1- take all the rods with hooks and drill a 3/32 hole in each blob of epoxy where the hook is. (the hole should be one size larger then your wire). Try not to hit the hook when drilling...
2- stick the long rod for the displacer through the little hole again.
3- poke through (or drill then poke through) the center of the displacer and epoxy. Make sure it's on GOOD. It's a REAL pain in the butt when it falls off and you've glued everything together... Just trust me on that. ;)
4- Glue the top plate onto the middle piece. I'd suggest hot glue, it works better. I would be great to use it on the bottom, but it would melt. Molten parts under any sort of pressure causes problems!

Bring out the PVC, mark and cut a 5 inch section. As seen in the fifth picture, mark a line down the length of the cut segment. This is a guide to help us cut straight. Once the marker dries, cut it in half!

Now to drill the holes for the crankshaft

Here's the process:
1- Stand the PVC sections you cut about where they'll be when everything is glued down.
2- Keep them there! a dab or two of hot glue may prove invaluable here, or an extra set of hands! (note, DO NOT MAKE THE GLUE JOINTS PERMANENT! We still have plenty of adjustments to do!)
3- Thread the displacer linkage onto the crankshaft
4- Lift the crankshaft until the displacer just starts to lift off the bottom. It should not be touching, but almost. If the crankshaft is horizontal (as it should be) mark where the ends are touching the PVC segments.
5- drill at the level of the marks. Then, move just above and below the hole and drill two more holes for a total of three holes per segment. The holes should only be 1-2 millimeters apart.


Chances are your previous attempts at leveling for the displacer wasn't exactly right. Now you have some adjustability!

Finally epoxy or hotglue one segment right behind the copper pipe. leave the other one unglued for the moment. It makes everything much easier to adjust.

Step 10: Test

Attach the piston to its lever arm, and slide on to the proper position on the crankshaft. It take some wiggling and some finagling, but slide it through the middle hole on the PVC piece you glued next to the copper pipe. Slide the lever arm for the displacer on the crankshaft. It takes some wiggling, and a little work, but attach to the displacer rod. You may need to change how the hook on the bottom is bent so that you can get it on the rod.

Finally put the second PVC part on in line with the other PVC and displacer rod.


Turn the crankshaft.
1-Does anything hang up? If the piston isn't moving properly, is it lined up like you marked? if no, remove, and twist the lever arm until it does line up.
2- when turning the rod can you make a full rotation? if you can't, check the displacer, does it move all the way up and down? if it's trying to go too high, move the crankshaft down a hole, if too low, raise it a hole. If it doesn't make a complete turn because it's trying to go too high and too low, lessen the bend in the crankshaft. Increase if there's too much of a gap.

If it turns over nicely, take out your peanut butter top and drill a hole the size of your rod in the middle of it. Attach to the side of the crankshaft closest to the copper pipe. It should be a snug fit, so don't glue it yet.

3- the moment of truth, does it work??? try different heat sources, hot water, candle, tea candle tin filled with alcohol. Obviously don't melt the plastic with too much heat. Turn the shaft and see what happens. One way should be significantly easier then the other, this is the way your engine runs.

After the metal heats for a bit you should have a few things happen when you spin the shaft
1- it runs great
2- nothing
3- it kinda moves, the piston just doesn't move high or low enough and will not cooperate.

1 yippee! move to the next step
2- make sure all your glue joints are air tight, Also, make sure nothing is snagging or hanging up. Add some oil to the joints and try again
3- make sure something isn't causing too much friction, add oil to the joints and try again. Check for leaks. And finally, try making the bend in the crankshaft for the piston shallower.

Once you get it running, move to the next step!

As a note, a CD can be used instead of a peanut butter lid... It's just a bit harder to attach...

Step 11: Tune

Basically, you're done... BUT, let's tune it up a bit.

Check for these these things:

over stressing parts (trying to make them do more then they want to do)

Basically add some oil (not much, but some) adjust parts that are causing problems, and keep everything sealed up tight. Also, we need to counterbalance the displacer.

First, go ahead and glue the other PVC piece down as well as the peanut butter top. Pull out the fan weight (or the penny or whatever) and start gluing it around on the wheel (use doublestick tape until you find the right spot) until you get the best preformance. This will probably be opposite the bend in the crankshaft, but not necessarily.

You're done go run your engine!

Step 12: How It Works:

Here's how it works (see first "picture")

first, either most the air is in the hot, or it is in the cold side, the flywheel makes sure this is the case.

1-air is forced into hot side (for sake of example) usually by someone spinning the flywheel.
2-air expands and pushes piston outward (stroke)
3- air is transferred to cold side out of hot side
4- air is all in cold side and begins to contract
5- cold piston is "sucked" down because of contraction.
6- flywheel pushes air back to hot side
7- repeat

Once you get the base concept down, it's not that hard, like the balloon, we're expanding and contracting air.

Now, one key factor, the animation is a alpha type engine, we're building a gamma type engine. The only difference is, there's a single chamber where one side is hot, one side is cold. a piece of foam (which only takes up space) is moved from the hot side to the cold side to push most of the air to one side or the other. Because most of the air is at the hot or cold side, a single piston either moves up or down because of the expansion or contraction. It's the same thing, just re-organized. See the second picture for a animation.

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