Introduction: Simple Coke Can Engine

About: Scrap To Power - check out my website for more projects
This is a simple coke can Stirling engine you can make in under an hour. No epoxy or RTV needed, just super-glue. It's all supported by steel wire, with spade connectors for all of the bearings.

Important note: It has been found that aluminium drinks cans need additional cooling around the top because the aluminium is so thermally conductive. Use steel cans if you can, such as Pepsi, Tango etc. Scraptopower has many other plans for simple Stirling engines, have a look here.

Thanks to David Williamson for the diaphragm design/ construction method. Check out his website here!

Materials1 Coke can
  • Steel wire wool
  • 1.6mm steel wire
  • Spring paper clip
  • Normal paper clip
  • 0.4-0.6mm fishing line
  • Super glue
  • Thin cardboard from a cereal box
  • A balloon
  • 6.35mm electrical connector/spade connectors .

Step 1: Open the Can With a Can Opener

Open the top of the can with a can opener.

Step 2: Bend a Paper Clip

Bend a paper clip into this rough shape, this is so that you can tie the wire onto the displacer later on

Step 3: The Displacer

Roll the steel wire wool around a bic pen, when it's a little bigger then the can opening, stop rolling the wool and cut it to size. Cut it down to about 2/3rds of the height of the can. Thread the paper clip you formed earlier through the centre of the steel wire wool. Tie on about a foot of fishing line to the hook in the paper clip. Squeeze the displacer into the can. It's a tight fit, but it can be done

Step 4: The Diaphragm

Draw two circles on the cardboard about the same diameter as the opening in the top of the can. Don't pierce through the cardboard with the point of the compass. Inflate balloon then super glue the cardboard disc onto the balloon, there's usually a slightly deformed part of the balloon - this is roughly the centre. Glue it on here. Deflate the balloon and cut off the neck.Turn the balloon inside out. Cut off the balloon around the centre.Glue the cardboard disc over

Step 5: Fit the Diaphragm

Use a sewing needle to pierce a hole through the centre of the cardboard discs and  thread the fishing line through that hole. Stretch the balloon over the can. Check that the displacer can be moved up and down freely.

Step 6: Cut the Main Bits of Wire

Cut two pieces of steel wire about a metre long. Mark the approximate length of the bearing supports by making a bend around 15cm from one end.

Bend the wire around the top of the can and twist it  to secure it.

Do the same on the other side.

Step 7: Make the Base

Bend the two 15cm pieces upwards, these will form the bearings for the cranks. The rest of the wire is bent downwards and formed into a big circle to support the coke can. I just twisted the wires together.

Step 8: Cut the Bearing Supports to Size.

Measure from the top of the can and cut the two bearing wires down to about 15cm. Crimp on two spade connectors for the bearing points

Step 9: The Cranks

Cut a piece of the steel wire about a metre long. Bend the displacer crank, this part should be bent out around 25mm.
About 5mm along from this, and rotated around by 90 degrees, start forming the two crank arms for the diaphragm.
The diaphragm cranks arms should be a short a stroke as possible, 2 - 4mm is good.

You should have about 80cm worth of wire left to form the flywheel. About 30mm from the diaphragm crank arm bend the wire in the opposite direction to the displacer crank arm. This is so you can counter balance the displacer it later on. Then about 12 cm along, start forming the circle for the flywheel.

Step 10: The Displacer Connecting Rod

Make the displacer connecting rod as above. To get the right size, thread the cranks through the bearing holes, and line it up as you make it.

Step 11: Diaphragm Connecting Rods

The diaphragm connecting rods are made in the same way. Start by forming a half-circle curve on the wire the same as the cardboard disc. You need two of these the same. Crimp connectors on the end.

Step 12: Assembly

Fit all of the connecting rods on the crankshaft.

Glue the ends of the diaphragm connecting rods to the cardboard discs using super glue. Keep an eye on the fishing line so it doesn't get glued down too!

Step 13: Tie on the Displacer

Tie the fishing line onto the displacer connecting rod. Make sure the displacer is moved all the way up and down by the cranks without getting stuck. When your happy, super-glue the knot so it can't come undone.

Step 14: Secure the Flywheel

Secure the end of the flywheel using a spring clip. This also counter balances the displacer. It's really important that you counterbalance the displacer - the engine won't work if you don't.

It's finished now! All you have to do is light a candle under the coke can and let it heat up. Once it's hot, turn the flywheel to start the engine.

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