Printable PDF Templates

SFA Stirling Engine Project

 » Movie 1 - Rapid movie engine
 » Movie 2 - Engine with a cork
 » Movie 3 - A little wobbly but it works!
 » Movie 4 - Foil heat funnel and screws on the flywheel
 » Movie 5 - First working Engine in 2004
 » Movie 6 - Zoom in of two engines

Parts List

Getting Started

To begin you can use these Printable PDF Templates to mark your cuts on each can.

Ring Stand - Use the top part of a diet shake can for the ring stand. Cut off the top of the can with a can opener. The tapered top will fit under the pressure vessel. The legs can be bent to adjust the height of the pressure vessel over a candle flame. You can also drill holes in the legs to attach it to a wooden base. The width of the legs can be about 2cm to allow a candle fit between them. The ring height is also about 2cm.

Pressure Vessel Bottom - Use the bottom of a diet shake can for this part that is 2 1/2" high. The 1/4" hole (not shown) should be drilled 1/2" from the top to allow air to enter into the PVC elbow. The candle flame will be in contact with the bottom of this can. You can attach the ring stand to the bottom of the pressure vessel using JB Weld.

Pressure Vessel Top - Use the bottom of a soft drink can for this part that is 1" high. The tapered bottom of this can will fit into the pressure vessel bottom. This part can hold ice to make the engine run faster. A hole should be punched in the center with a straight pin that are at least 2" in length. Glue a 1/4" (inner diameter) nut using red RTV over the top of the hole. Cut a flat 1/2" square out of a steel can (e.g. shake can or peanut can). Note that the 1/2" square must be made of steel. Punch a hole in the center of the flat square with a straight pin. The pin should slide smoothly through this hole with no side to side movement. This is intended to be a fairly air tight seal; although there will be some air leakage. Glue the square onto the nut with RTV. The hole in the square should be centered over the hole in the pressure vessel top.

Displacer Bottom - The displacer should have a total height of 1¼". There should be no air leaks into the displacer. The displacer should be smooth and fit inside the pressure vessel with about 2 millimeter clearance when centered inside the can. Method 1: This can be the bottom of a tall 12 oz that has a circumference that is about 10mm less than a soft drink can. Keep the bottom. Method 2: This part can also be made using the wall of soft drink can with the top and bottom cut off. The can is cut vertically and glued (with hi-temp epoxy) together to form a 1-1/4" high cylinder with a diameter of about 95% of its original diameter. When the can is glued to form a cylinder, the overlap will be about 10 millimeters (assuming a 65 mm diameter can). The bottom of a soft drink can is trimmed to just fit inside the bottom of the displacer (concave out).

Displacer Top - The bottom of a soft drink can is trimmed to just fit inside the top of the displacer bottom (concave in). Insert a 2" straight pin through the displacer top. A circular template (the diameter of the aluminum can) made from graph paper is useful for finding the center of a can. If the pin has and eye, then you can feed a strip from an aluminum can through the eye and wrap it around the pin. This will keep the pin from sliding out of the displacer if the eye is on the inside of the displacer. Use JB Weld epoxy to attach the pin to the displacer top. Then epoxy the displacer top to the displacer bottom. Make sure the the pin is held vertical as the JB Weld hardens overnight.

Crankshaft - Use 7 inches of coat hanger wire (or equivalent) to make the crankshaft. Make sure there is a 90 degree angle between the displacer and power diaphragm connections as shown on the last page of this PDF file. That is, the displacer is 90 degrees out of phase with the power diaphragm.

Crankshaft Supports - Make two supports that will be attached to the pressure vessel. Method 1: Cut out two 12cm x 3.4cm sections from a diet shake steel can. Method 2: Cut out four 12cm x 3.4cm sections from aluminum soft drink cans. Make a pair of supports by gluing (with JB Weld) two sections together for stiffness. Punch a 3/32" hole in each support 1/2" from the top as shown on the last page of this PDF file. The hole should be just large enough to allow the crank to turn freely; but there should be no up-down or side-to-side play in the crank.

Construction

1. JB Weld can be applied with a toothpick or popsicle stick. Red RTV can be used to seal and glue some parts on the outside of the Stirling engine. Its cheaper and dries faster than J-B Weld, but its not as strong. Do not use RTV on the displacer because it has a high friction coefficient and will cause the displacer to drag if it rubs against the side of the pressure vessel. Use drops of superglue or slivers of tape to temporarily hold parts in place while epoxy sets.

2. Use JB Weld to attach the pressure vessel bottom to the ring stand.

3. Insert the displacer into pressure vessel. Place the top on the pressure vessel and gently push the top into the vessel. Note that the straight pin should protrude at least 1/2" from the hole in the top. Verify that the displacer moves smoothly inside the pressure vessel when the displacer rod (straight pin) is moves up and down. Glue the top onto the vessel with RTV. This joint must be air-tight. Once the glue has dried, bend 5/16" inch of the end of the straight pin to a 90 degree angle. Be careful not to bend the portion of the pin that must pass through the hole in the top of the vessel. Optionally, you can instead use JB Weld to attach a shorter piece of a straight pin the top of the displacer rod to make a 5/16" horizontal rod.

4. Fit the flywheel CD onto the crank. You can attach a wire nut to the end of the crankshaft and wrap electrical tape around it until it just fits into the hole in the CD. Turn the crankshaft/flywheel and eliminate as much wobble as possible.

5. Install the crankshaft in the support holes. With the crankshaft in place, use RTV to attach the supports to the side of the pressure vessel so that the 1/4" holes in the pressure vessel and one of the crankshaft supports line up. Note that the crankshaft is correctly oriented with respect to the 1/4" hole in the pressure vessel as shown on the last page of this PDF file.

6. Use a knife or dremel tool to shape the smaller end of the 3/4" to 1/2" PVC Elbow so that it saddles the side of the pressure vessel over the 1/4" hole. The 3/4" end of the PVC elbow should point up. Note that the outer diameters of the PVC elbow are actually 1-1/4" and 1" respectively. Also note a 3/4" to 3/4" PVC elbow can also be used instead. Use RTV to attach the PVC elbow over the 1/4" hole in the crankshaft support and pressure vessel bottom.

7. Install the displacer connecting rod (aluminum wire or paperclip wire) between the crankshaft and the 5/16" horizontal part of the displacer rod. (See TheRecentPast's stetch.) Adjust the wire so that when the crank is turned, the displacer comes close to the top and bottom of the pressure vessel but does not touch. Tape a washer or coin to the side of the flywheel to counteract the weight of the displacer. Turn the crank and adjust the location of the washer until the crank turns smoothly (i.e. the weight of the washer counterbalances the weight of the displacer). If a point can't be found, a larger washer may be needed.

8. Cut a rubber diaphragm from a helium quality balloon. The diaphragm should be cut from a spherical portion of the balloon so that it is dish shaped. The diaphragm should be air-tight and loosely fitted, so that it does not stretch through the entire motion of the crank. At the top and bottom of the stroke the diaphragm should be slightly taut. The dish shape of the diaphragm should help achieve the range of motion without stretching the diaphragm. It is important that the diaphragm not resist (by stretching) movement of the engine. Use a tight rubberband around the PVC opening if the balloon does not fit tightly. Optionally, apply superglue to the rim of the PVC elbow and press the rubber diaphragm onto the end cap.

9. Install the power diaphragm connecting rod per TheRecentPast's stetch. Note the orientation of the foot. Attach a square of rubber balloon to the top of the connecting rod foot with superglue. Attach the covered connecting rod foot to the diaphragm with a drop of superglue. Verify that the end of the wire is turned up and will not stick into the diaphragm. The diaphragm should move into and out of the end-cap when the crank is turned but should not stretch.

10. 1/8" strips of aluminum cans can be wrapped around the crankshaft to keep it and the connecting rods from sliding from side to side. Here is an example engine with these strips.

11. Optional: Fasten the legs of the ring stand to a wood board with a wood screws.

Running the Stirling Engine

Movie

1. The engine should run off the heat from a tea light candle, assuming the flame is as intense as an average candle. Light and place the candle under the pressure vessel. After 30 seconds or so, gently spin the crank in the direction in which the displacer rises before the diaphragm.

2. This engine will rotate at 120 RPM or greater depending on the heat produced by the candle flame. If the flame is too small, the engine will not work. Cooling the top with water or ice may help, just don't let the water get inside the engine. The more water put on top of the vessel, the cooler it will stay and the faster the engine will run. A collar can be built around the displacer rod to keep water out of the vessel and the sides of the vessel top can be built up with a larger collar to make a space for holding water on top of the vessel.

3. The displacer, pressure vessel, diaphragm, etc. have to be air tight. There should only be minuscule air leakage around the pinhole when the engine operates. You can check it by putting a drop of oil on the pin hole. There should be a few small bubbles formed when the displacer moves up and down.

4. Minimize all binding and friction using drops of oil. The flywheel should turn freely. Verify that the flywheel is balanced with the displacer connected to the crankshaft and the diaphragm disconnected. The displacer should not hit the top or bottom of the pressure vessel. The diaphragm should not stretch or tighten during operation. It should "pop" in and out.

Additional Information

This project is part of an engineering course team project at Stephen F. Austin State University. The latest version of these plans can be found at http://www.physics.sfasu.edu/astro/courses/teamwork/StirlingEngine/stirling.html. This work was inspired by TheRecentPast and is a modified version of the plans found at http://www.geocities.com/therecentpast/.

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