This Instructable is a design for constructing a miniature wooden car that is powered by a Stirling engine. All of the materials that are required can be found at a variety of local hardware, department, or grocery stores. While the Stirling engine is not a very efficient method for powering a large vehicle, it is an interesting and easily observable example of a basic concept of thermodynamics. I hope that you all enjoy working on this project, and that this Instructable will be able to give you clear guidance along the way.
Note: The engine design is based on the video above, which is not my own content or media.
The Stirling engine essentially consists of five basic parts: the cylinder chamber, the displacement cylinder, the diaphragm, the crankshaft (axle), and the wheel.
Step 1: Materials and Supplies
Here is a list of the materials that I used, though similar alternative materials may also work:
-Steel Can with lid removed (I used a can of garbanzo beans with a height of 11.25cm and a diameter of 7.50cm)
-Metal clothes hanger
-4mm square balsa wood
-Balloon (9 - 12 inch size, NOT water balloons or other smaller sizes)
-Thread (Polyester or heavy-duty variety)
-Cardboard (a few very small pieces will do)
-Super glue, hot glue, and/or wood glue
Step 2: Tools and Machines
Here is a list of various machines and tools that I used for making the Stirling engine car, though alternatives will certainly work as well:
- Needle-nose pliers
- Drill press
- Hole saw
- Rip saw (cutting parallel to the grain of wood)
- Cross-cut saw (cutting perpendicular to the grain of wood)
- Adjustable clamps
- Hot-glue gun (optional)
- Tin snips
Step 3: Frame and Body Preparation
To begin, cut out a piece of poplar wood that is 10.3 cm wide by 43.2 cm long. This will be the base of your car.
Beginning at one end of the base, measure 13.65 cm and draw a line across the width. Measure 10.5 cm further from this line and draw another line across the width of the base. The area between these lines is where the frame for your engine will sit. From your first line, draw another line across the base that is 21.25 cm away. Draw a line across the base at this point to mark where the supports for the axle of your engine will go.
Step 4: Engine Holder
Taking poplar wood, cut out three pieces with dimensions as follows:
2 pieces- 103mmx86mm
1 piece- 103mmx103mm
Use the square piece as the base, and use tacks or small nails to attach the upright sides, as shown in the picture.
Using wood glue or another variety of glue, secure this holding frame to the base in the location shown in step 3 (132mm from one end and 191mm from the other).
Step 5: Making the Displacer Cylinder
Using the hole saw (use a saw bit that is just smaller than the opening of the can), cut 7 cylinders out of the balsa wood. Glue these cylinders together, one directly on top of another, and allow to dry (using clamps will likely aid in quickening the drying process).
Step 6: Forming the Axle
To create the axle that will be turned by your engine, start with a metal clothes hanger. Use tin snips to cut apart the hanger and remove the long straight bottom piece (I recommend saving the other pieces, just in case you need to start over).
Cut off a piece that is 30 centimeters long.
Starting from the center, use needle-nose pliers to bend the clothes hanger into the shape as shown in the picture above (measurements are noted). Please also note that the axle should be symmetrical, so the dimensions are the same on either side.
Additionally, cut out a another 30 centimeter long piece for the rear axle. This axle can be kept straight, and does not need to be formed as the other one.
Step 7: Supporting Rods
Obtain a 4 millimeter square balsa wood rod. Cut off two pieces that are 13.3 centimeters long. Drill a hole 9 millimeters away from the end of each piece that is just larger than the diameter of the clothes hanger. Slide one supporting rod onto each side of the axle, as shown above.
Step 8: Axle Supports
Cut four rectangular axle supports, with dimensions 7.45 cm wide by 6.00 cm high. Find the center of the plane side of each support and drill a hole that is just larger than the diameter of the clothes hanger. Glue these to the base at the locations shown in the picture in step 3.
IMPORTANT NOTE: You will need to attach one axle support to the base, insert the axle, and then attach the other support on the other side. The front axle should have the support rods attached.
Step 9: Engine Cylinder and Diaphragm Assembly
In this step, we will assemble the engine. Take your displacer cylinder (Step 4) and fill the hole on one end with a small screw that fits snugly in place. This will make it less likely for air to escape to unintended pathways. Next, take another screw, and begin to screw it into the hole on the other end. Before fully screwing this screw in all the way, securely tie the thread around the screw. Once firmly tied in place, finish inserting the screw.
Next, take a balloon, and cut it around where the neck starts to widen (it is better to cut off less initially, because you can always cut off more later if necessary). Stretch the balloon over the top of the can. Using a marker or pen, make a mark at the top center of the balloon. Remove the balloon and, using a needle or small tack, run the thread that is attached to the cylinder up through the bottom of the balloon.
Once the thread has been pulled through, you can remove the needle/tack.
Step 10: Connecting the Engine to the Axle
Approximately 1 centimeter away from the thread, poke two thumbtacks through the balloon, one on each side of the thread. Next, place the displacer cylinder inside of the can and carefully place the balloon over the can's opening. Use two rubber bands two secure the balloon in place. Insert the engine canister into the engine holder, and use some variety of tape (duct) or glue (hot glue) to secure it in place. Attach the support rods to the diaphragm by pushing the thumbtacks firmly into the ends of the rods. Next, run the thread up to the axle.
Taking a paperclip, form an attachment in order for the thread to spin freely around the axle (shown in picture above). Use snips to cut off any excess material. The paperclip should be secure, yet able to freely spin. Pull the thread tight, and tie it securely to the paperclip mount. Cut off any excess thread with scissors.
Step 11: Heat Source
From poplar wood, cut out two rectangular pieces, 78mm x 40mm.
Glue the two piece together, one on top of the other, and glue them to the base, directly behind the can. These will be the supports for your heat source.
Next, glue two tea candles side by side on top of the support structure. Ideally, the flames should be located very close to the center of the can's base, as shown above. Be careful to avoid burning yourself as you light the candles.
Step 12: Wheel Construction and Attachment
Using a hole saw, cut out four circular pieces of poplar or balsa wood, 12 centimeters in diameter (these will be the wheels of the car). Slide a small washer onto each side of the two axles, and then slide the four wheels into place. Forcefully yet carefully bend over the excess axle length into the side of the wheel, and secure it in place using hot glue or staples.
Step 13: Making the Car Run
Now that you have assembled the car, it is time to make it run. First, light the candles, and allow the engine cylinder to heat up. You will need to kick-start the engine, by giving the front wheels some good, hard spins for 1-2 minutes. Eventually, the engine should kick in and begin to power the vehicle.
This project took a decently long period of time. Most of the time was spent constructing the different parts, while actual assembly did not take as long once everything was repaired.
In terms of cost, this is a relatively inexpensive project. All materials can likely be obtained for a total of less than $30.
A number of improvements could potentially be made. Having a diaphragm balloon that has some slack but still retains some elasticity is of extreme importance. Another improvement could be using a heat source that supplies a more substantial amount of heat (blow torch, alcohol burner, etc.). Also, using a stronger thread would improve results. Additionally, if one were to greatly reduce the mass of the displacer cylinder, it would be able to move more effectively and generate more motion for the car.
Note: I have not yet successfully gotten the car to run. I am submitting this for a school project, and plan to complete the car and make it functional within the next week or two. I intend to upload a video of it working as soon as such is available.
If you have any suggestions, criticism, or concerns, please let me know in the comments. Enjoy!