Step 1: Make The Displacer:

1. First off, the displacer should look something like this . I form my displacer so that it is about 1/2 as tall as the can, and so that it is narrow enough to slide up and down inside the can with very little friction. I try to make it look like a cylinder, but it often ends up looking like a ball. The balls work, too.
2. Get about 1.5 "biscuits" of steel wool. Steel wool comes in squashed rolls, that seem biscuit-like to me, so that's what I call them. Also cut about 8" of 20 gauge steel wire. Use pliers to make a small loop (1/4" to 1/2" in diameter) in the end of the wire. Unroll the full biscuit of steel wool, and place the wire on top of it, near the end of the steel wool, with the loop sticking out . Begin to roll the steel wool around the wire. After one wrap, squish the steel wool so that you'll end up with a cylinder that's about half the height of the can. Then bend the wire upward to the top of the steel wool. Then do another wrap and bend the wire back down. Wrap the rest of the steel wool from the full biscuit.
3. Test the fit in the can. If you have a nice cylinder that's almost as wide as the can and 1/2 as tall as the can, you're done. But most likely you will have to do some shaping and add some more steel wool. That's where the other 1/2 biscuit comes in.
4. Keep working the displacer to try to make it about 1/2 as tall as the can, and just narrow enough to slide up and down with ease. You can tearrthe steel wool and then mash it together so that it sticks. It's a little bit like working with clay. Or maybe like weak Velcro.  Here's a top view of how it should look when you're done.the steel wool and then mash it together so that it sticks. It's a little bit like working with clay. Or maybe like weak Velcro.  Here's a top view of how it should look when you're done.

Step 2:  Add The Displacer String and Pull Tab

For this step you're going to need...

• About 1 foot of braided fishing linee
• A 1" x 2" (roughly) strip of aluminum foill
• A 1" square of duct tapee
• A sewing needlee
• A 3-d printed "pull tab""

Here are the Instructions:Here are the Instructions:

1. Attach the fishing line to the displacer loop: First, roll/pinch the aluminum foil into a thin stick. Poke this stick and one end of the fishing line through the wire loop in your displacer. Wrap the end of the fishing line around the foil stick several times. Finally, squish the aluminum foil on the wire. Compress it so that it stays put. Pull the fishing line to confirm that it is secure.
2. Bend the loop and aluminum so that the fishing line connects to the displacer at its top edge (because the string will exit the can at its edge).
3. "Fish" the line through the tiny can hole, using the sewing needle: First, place a small square of duct tape over the hole, on the outside of the can. Then place the displacer inside the can, with the line near the tiny exit hole. Thread the fishing line through the needle. If the end is frayed, cut it more cleanly. If all else fails, use a razor against a piece of wood. From the inside of the can, poke the needle through the topmost part of the hole.
4. Attach the pull tab to the other end of the fishing line: With the displacer sitting in the bottom of the can, and oriented so that the string is exiting directly from the can, pull the fishing line taut. Don't lift the displacer off the bottom of the can. At a point on the line about 1.5" from the can, slide the line into the pull tab's notch. Then wrap the free end around the pull tab several times. Then pull the free end into the notch to lock it in place. Cut off the excess, but leave a little (at least 1/4") hanging out.
5. Test your displacer: Grab the tab in one hand and the can in the other. Use the tab to raise and lower the displacer. If it looks like it's moving up and down easily (causing air to be displaced down and up), move on to the next step. If not, figure out what's wrong and make adjustments. You may need to squish your displacer into a better shape.

Step 3:  Add The Power Piston Membrane

Get a disposable glove or a balloon. If you're using a balloon, you can probably just cut the neck off and stretch it over the top of your can. Hopefully it will stay in place on its own. If you're using a disposable glove, you will need to clamp it in place. Here are the instructions for using a glove...

1. Cut the palm out of the glove. Since a disposable glove's palm and the back are the same, one glove should give you two membranes.
2. Cut about 1 foot of 20 gauge wire.
3. Form the wire into a loop. Use locking pliers to squeeze and hold together the two ends of the loop.
4. Place the loop around the top of your can. Use the pliers to twist the wire until the loop just begins to tighten on the can. Then "untwist" a little to expand the loop and remove it from the can. Your loop should now be a nice circle, ready to hold the membrane in place.
5. Have a helper place the membrane on the top of the can. Lower the loop over the membrane and twist the wire to tighten. If you over-tighten, you may break the wire. If you under-tighten, your cylinder may leak. Try to get it tight without breaking the wire, but remember that there's plenty of wire.
6. When your membrane is tight and in place, you can trim it, but leave maybe 1/2" inch. If you have to remove the membrane, this extra bit might be enough to enable you to put it back on.
7. Clip off excess wire, but as with the membrane, leave a bit -- maybe 1/4".
8. Add a protective piece of duct tape over the edge of the membrane closest to where the displacer line comes out.  This will protect the membrane from abrasion as the line slides up and down.

 These are the directions for the glued-on version of the fixture.  If you have the screwed-on version, adapt accordingly!

1. Get one of the 3-D printed power piston fixtures.
2. Dribble a little cyanoacrylate glue ("super gue") onto the center of the membrane.
3. Place the fixture on the puddle of glue, and smear it around a little, to get glue over all of its contact points. Orient the fixture so that its hole points to where the fishing line exits the can.
4. Under a fume hood, or with some other type of adequate ventilation, give the membrane a squirt of accelerator. After the accelerator is applied, the glue should cure within 20 seconds.
5. Wait until all of the accelerator evaporates to touch the membrane.

Step 5:  Cylinder Heat Test And Power Piston Crank Measurement

Secure your cylinder on a stand and have a ruler ready. Light a burner beneath the can. As the can begins to heat up, grab the pull tab and use it to raise and lower the displacer to its highest and lowest points. You should begin to see the the membrane rise and fall due to the expansion and contraction of the air in the cylinder.

1. When the rise and fall of the membrane seems to have reached its peak, measure the distance that the power piston fixture is rising and falling. Write this down. This measurement will determine the size of the power piston crank.  Here's what mine looked like at its high point .  And here it is at its low point. .  I estimated it was traveling up and down a total distance of about 0.8cm.
2. Remove the flame. For the next few measurements, you won't need it.
3. Now grab the pull tab again and measure how far the pull tab travels as you raise the displacer to its highest point and then let it fall to its lowest point. Write this down. This measurement will determine the size of the displacer crank.
4. Now measure the distance from the center of the power piston fixture to the edge of the can where the fishing line exits. Write this down. This measurement will determine the distance between the two cranks.

Step 6: Prepare Some Straight Rods For The Crankshaft And Pistons

Cut two 10" pieces of 14 gauge wire. Tighten one end of the wire into the chuck of a drill. Secure the other end with locking pliers. While a helper is holding the pliers steady, use the drill to twist the wire until it is straight. Release the wire.  .  One end will be used for the crankshaft.  The other end will become piston rods.

Step 7:  Shape The Crankshaft

1. Find the crank measurements that you wrote down in step 7. Divide the measurements by 2 to get the right crank lengths! The reason for this is that each crank rotates above and then below the crankshaft axis, so to lift the displacer from its bottom point to its top point, the crank needs to extend half that distance below the axis and then it needs to rise to half that distance above the axis -- 1/2 plus 1/2 equals the full distance that you measured in step 7.
2. Bend the displacer crank first. Measure about 8cm from one end of the longer wire and make a mark [This is going to be the flywheel end of the crankshaft, so that's what I will call it -- the "flywheel end."]. At that mark, use pliers to make a sharp 90 degree bend. From that bend, make a mark for the crank length (1/2 of the measurement from step 7). About 1cm or 1/2" further along the wire, make another 90 degree bend back in toward the axis of rotation. You'll be making a sharp "U" shape. Now bend the wire 90 degrees again so that, when you're done, your main axle continues in a straight line from the "starting end" to the other end, but with the U-shaped displacer crank sticking out of it at 90 degrees.
3. In step 7, you measured the distance between the displacer crank and the power piston crank. Measuring from the leg of the displacer crank closest to the flywheel end of the wire, make a mark at which you will begin bending the power piston crank.
4. Bend an offset power piston crank.
5. The power piston crank needs to be offset from the displacer crank by 90 degrees in one direction. To understand clearly what I mean, look down the crankshaft with the flywheel end pointing away from you. Rotate the displacer crank to the 12 o'clock position. If the displacer crank is at 12 o'clock, a 90 degree offset means the power piston crank should be at either 9:00 or 3:00.   In this pictue, the taller displacer crank is at 12, and the shorter power piston crank is at 9.
6. Aside from making sure you have this offset, the method of bending this crank is the same as the method displacer piston crank. To determine the power piston crank length, use the measurement from step 7 and divide by 2.

1. Slide one or two thin plastic washers onto to the flywheel end of the crankshaft.    Then push the end through a flywheel, so that it comes out the plastic side.
2. Adjust the flywheel until it spins freely without hitting the wooden stand.  Then tighten the set screw.
3. Mark the crankshaft where it exits the leftmost piece of aluminum  .  Then remove the crankshaft and flywheel and bend the crankshaft at this spot.
4. Give the flywheel a little spin. Make sure the cranks are rotating freely, and that they are where they should be. If there's friction, locate its source. Get everything aligned as well as possible. You may need to do some judicious bending.

Step 9:  Connect The Piston Rods

Get two piston rod connectors and snap each of them onto a crank. Then find the straight, 6" rod made of 14 gauge wire that you set aside in an earlier step.

Make the power piston rod:

1. Make a right angle bend about 1cm long at the end of the rod.
2. Insert this bend through the hole in the power piston fixture.
3. Rotate the power piston crank to 3:00. Keep it in this position while holding the wire rod next to it. Mark the wire rod half-way up the plastic rod connector.
4. Cut the rod where you marked it.
5. Remove the plastic connector from the crank. Insert the rod half-way into the connector and tighten it in place with a set screw.
6. Pop the connector back on the rod and insert the bottom elbow through the power piston fixture.

Make the displacer Rod:

1. Make a right angle bend about 1cm long at the end of the rod.
2. Insert this bend through the hole in the power piston fixture. Once it's through, you can bend it a little more or squeeze it snug to keep it in place.
3. Rotate the displacer crank to 12:00. Keep it in this position while holding the wire rod next to it. Raise the rod to pull the displacer to its highest position. Mark the wire rod half-way up the plastic rod connector.
4. Cut the rod where you marked it. Insert the rod half-way into the connector and tighten it in place with a set screw.

Check the power piston rod for correct positioning:

1. Power Piston Rod Check: Turn the flywheel slowly. You should see the power piston rod pushing the membrane down and pulling up equally, with the membrane at equilibrium position half-way in between. If that's not the case, loosen the set screw, raise or lower the piston rod, and re-tighten the set screw.
2. Displacer Rod Check: Turn the flywheel slowly. You should see the displacer rod raising and lowering the displacer through its entire range, but not beyond. If you see the string going very slack, adjust the piston rod upward using the set screw. If you notice that there's a lot of tension when the crank is at the top (12:00), adjust the rod downward.  Having some slack at the