Recently I saw a video of a remote controlled boat powered by a miniature steam engine and was instantly hooked on the idea. After doing a bit of research I found miniature steam engines cost hundreds of dollars or require some very advanced skills and tools to build. Yet looking at the actual mechanism which allows them to run they are really quite simple so I decided to try and make one on the cheap.
The point of this project was really to see how cheaply and easily a miniature steam engine could be built. I built this engine in one day and for under $10 in materials so I think it's safe to call it a success.
This engine is 7.2cm (2.8") tall.
Some Things to Note:
First off I should state that this steam engine is only a steam engine. This instructable does not include instructions on how to build a boiler to produce steam. Instead I run the steam engine on compressed air. If you don't have a compressor a bicycle pump works well too, it's just a lot more work for you. ; )
I should also note that even if you did build a boiler this engine probably wouldn't work well because many of it's major components are wood. In the presence of steam the wood would swell and warp causing problems. A simple solution to this problem would be to replace the wood parts with aluminum ones.
I am a very visual teacher so be sure to read the 'Image Notes' (hover your mouse over the yellow boxes on the images), it will likely make my instructions clearer.
How it Works:
You could read my lengthy description below or you could check out the totally awesome animation by the guys over at www.animatedengines.com, find it here! I should note that this animation is of a "double acting" engine, in that is has ports on both the bottom and the top of the cylinder where mine is a "single acting" engine with ports just on the top. This just means that the engine relies more heavily on the momentum of the flywheel to keep it running but is a lot simpler to build.
This type of engine is called an Oscillating Steam Engine. If you watch the video below you will see that the cylinder on this engine actually moves back and forth as the flywheel turns (it oscillates!), this action is what opens and closes the ports which let compressed air enter the engine and exhaust air leave.
The cylinder has one port at it's top which is pressed up against the main body of the engine. The main body on the other hand has two ports, one for the compressed air and one for exhaust. As the cylinder tilts to the right it aligns with the compressed air port allowing air to flow into the cylinder and push down the piston. This causes the crankshaft to turn, thus tilting the cylinder over to the left and allowing the air to exit the cylinder though the exhaust port as the piston comes back up. Then the process repeats.
Step 1: Materials, Tools, and Plans
Most of the materials and tools for this project you will likely already have around the house. The only things I had to buy were the brass tubing, tubing cutter, and some wire.
• 3/16" Plywood (aprox: 12x8cm)
• Retractable Pen (optional)
• Brass Tubing: (find some at your local RC hobby shop)
13/32" for the piston and 7/16" x 0.014" for the cylinder
• "Tea Light" candle
• Heavy washers with a diameter less than that of the tea light
• 5 Minute Epoxy Glue
• Plastic Tubing (to connect your compressed air supply)
• HomeDepot sprinkler marker flags or piano wire (~18AWG)
• Floral stem wire or piano wire (~24AWG)
• Q-Tips with plastic tube (not paper)
• Small elastic bands
• Plastic Wrap
• Drill (or better yet; a drill press) and bits
• Tubing Cutter ($5) - you should also be able to find one at most hardware stores.
• Pliers and Wire Cutter
• Empty Tin Can
• Razor Knife
• Vice (optional)
Attached are two PDF files. "Parts Only With Measurement" includes a layout of all the parts you will need to cut out of wood as well as the lengths for the wire and brass tubing parts. "Parts Only No Measurements" is exactly the same but without any measurements printed on the page; good for cutting out and gluing to your wood as a guide.
Some people are having trouble opening the attached PDFs, if you are too try the links below. Step 2: Cut the Piston and the Cylinder
Cut the cylinder and piston from two pieces of brass tubing. They do not have to be exactly the same diameters as I used but the smaller one should fit very snugly inside the larger one and still be able to slide freely. Your local hobby shop should have the correct sizes of brass tubing.
The cylinder should be 25.5mm long, and the piston 14.5mm.
Using a Tubing Cutter:
To use a tubing cutter align your cut with the cutters blade and tighten the knob, not too tight though as not to squish the tube. Slowly rotate the tube inside the device tightening the knob every few turns until the blade cuts through the tube. It may take a few practice runs, I ended up squishing the tube too much several times.
Scrape out the inside lip of the cylinder with a razor blade to ensure no burs are left to scrape up your piston.
If you don't have a tubing cutter you can buy one from Harbor Freight for $5.
Step 3: The Piston
First cut the wire (24AWG) for the piston rod (I used a thin piece of floral wire but any stiff wire will do), then make a 90 ° bend 3mm from one end.
Now take some sandpaper and scuff up the inside of the piston.
Next take a small piece of plastic wrap and cover one end of the piston tube, secure it with an elastic.
Mix some epoxy and fill the inside of the piston tube with it. Be very careful not to get any on the outside of the piston, also try to keep the tube pressed to the table so no epoxy will get out under the edges of the plastic wrap.
Now insert the piston rod (bent end first) straight into the epoxy.
To ensure that the piston rod stays at 90° you may want to push it through a piece of ~0.7mm foam first and glue that in along with the piston rod (see Images).
Alternatively you could try hanging the piston rod from something so that it is just 1mm or so above the table, this will ensure it stays perfectly vertical while the epoxy hardens.
Step 4: The Flywheel
Start by cutting the crankshaft wire. It should be a 45mm long piece of ~18 AWG wire. I used the wire from one of those little red flags you see stuck in lawns to mark the sprinkler system. If you can't find one Home Depot sells them. This size of wire is excellent because it fits perfectly inside of the plastic tube that Q-Tips are made of.
To make the flywheel I popped the wax out of a tea light (candle), inserted the crankshaft wire through a few pieces of wood to keep it from pulling out of the wax and glued them to the crankshaft, then I added some metal washers (to add weight). Next I put all this back into the tea light and poured its melted wax back in to hold it all in place. Hopefully the images below will better explain this process.
To melt the wax I put it in the bottom of a tin can which I had bent a bit of a spout into to make it easier to pour. Then put the can in a pot of boiling water on the stove until the wax melted.
Be sure to lay down a few layers of newspaper before trying to pour molten wax, I also wouldn't recommend doing this over carpet. Epoxy could also easily be substituted for the wax, I just didn't have enough epoxy to do it.
If I were to do it again I would drill a hole through the bottom of the tea light and run the crankshaft wire all the way through so that the motor could be easily connected to another device in order to power it. If you do this you should probably make the crankshaft wire a cm or so longer.
Step 5: Make the Wood Parts
The wood parts are to be made from 3/16" plywood. I bought mine from the craft department in Wal-Mart; $3 for a six pack of 7x3" sheets. You could also use aluminum, brass, Teflon, plastic or Plexiglas instead of wood. Just make sure whatever you use it has a nice smooth finish in-between the moving parts. You will find the plans for the wood parts back on the Materials Page.
3/16" plywood is easily cut, even with a razor knife. Cut both sides and go over it with the blade several times until the wood cuts. Sand the edges smooth. To cut the round crankshaft part start with an octagon shaped piece and sand the edges to a circle.
Now start by gluing the part Body 2 to Body 1. Drill the top two holes with a 3/32" drill bit. Drill the central hole the same size as the wire you used for the Cylinder Pivot Wire. Finally Drill the bottom hole the same size as the plastic tube from your Q-Tip.
Step 6: Cylinder Block
To build the cylinder block start by taking the wooden part "Cylinder Back" and sanding down the center gray area of it by about 1mm. This will make a smaller contact area between it and the body, thus reducing friction.
Now drill out the center hole in this part the same size as the wire you will be using for the "Cylinder Pivot" wire. Now drill out the top hole with a 3/32" bit.
Cut the wire for the "Cylinder Pivot" part and make a 90° bend 5mm from one end. Now, on the opposite side from where you sanded down 1mm on the "Cylinder Back" part you must cut a 5mm long grove from the middle hole towards the top hole, just deep enough for the 5mm of wire to rest in when it has been inserted through the wood. This is the side you will be gluing the cylinder to.
Start by drilling out the 12mm hole in the cylinder head before you cut out the square around it, unless you have a drill press such a large hole will be hard to align with a small piece of wood. This also helps it from splitting on you. Now cut out the 2.5mm deep grove in the other Cylinder Head part.
The next step is to glue the two cylinder head parts, the brass cylinder tube, and the cylinder back parts together. You may want to press some foam into the end of the cylinder tube to prevent any epoxy from dripping into it before gluing.
Epoxy the cylinder head to the cylinder then both of those to the 'cylinder back' so that they are centered horizontally and the bottom of the cylinder is aligned with the bottom of the cylinder back. The 2mm deep grove you cut in the second cylinder head piece must also line up with the top hole in the 'cylinder back'.
Step 7: Crankshaft
I added a small circle of wood around the outer hole in the wooden crankshaft part. This gives the piston rod a little more clearance and prevents it from creating more friction rubbing on the crankshaft. See the Image below.
Next drill the outer hole in the wooden crankshaft part the same size as your piston rod wire, then drill the central hole in that part the same size as the wire used for your crankshaft.
Now epoxy the part "Brace" to the flywheel side of the body just under the hole for the crankshaft, I also added a small brace to the piston side of the Body.
Now epoxy a Q-Tip tube into the hole though the body and to the top of the brace. You can now insert the crankshaft through the body, add a few washers made of free spinning Q-Tip tube between the flywheel and the body. Add more Q-Tip washers on the piston side to provide proper spacing so the face of the wooden crankshaft part will be under the center of this piston. This also helps prevent the wooden crankshaft part from accidentally getting glued to the body.
Finally trim off any excess length of crankshaft wire as it will collide with the piston rod if it sticks out at all from the face of the wooden crankshaft part. Now glue the wooden crankshaft part to the metal crankshaft wire (the other end of which is secured in the flywheel), fixing it in place.
Step 8: Finishing Up
First make a 90° bend in the piston rod 20.5mm from where it enters the end of the piston. Now insert the piston into the cylinder, then simultaneously push the cylinder pivot rod and the cylinder rod through the body and the crankshaft respectively. You will likely have to turn the crankshaft to make the hole for the cylinder align with the bend in the cylinder rod.
Now you just need a way to hold the cylinder tight up against the body. I used a spring from a retractable pen held in place with a screw on "prop-saver" from a model airplane. I also found just putting an elastic band around the piston and body worked quite well... if not better than the spring, this option is also much easier to remove than if you glued a cap on the cylinder pivot rod. An elastic or two should really be all you need here.
Lastly you need to connect one of the top two holes on the flywheel side of the body to a compressed air tank or pump. To do this I just glued some plastic tubing to the body; just do whatever works best for you. This motor works quite well for me on ~15psi. Turn on the air and give the flywheel a quick flick and the motor should start, if not try flicking it in the other direction. If you line it up just right the motor will even start without you flicking it. Switching which hole the air goes into will reverse the direction of the engine's rotation.
If your motor does not run first make sure everything spins fairly easily when turned by hand. If it doesn't try figure out what is stopping it. Next make sure that you did not accidentally get glue in any of the holes that supply air to the motor. Lastly try running the motor on higher PSI. Other than that there isn't much more I can suggest. You can try posting any questions in the comments, I'll see what I can do but I'm no expert on the subject.
Over all I am very pleased with how this little motor came out. It runs very smoothly, looks good and was really easy and cheap to build. Some possible improvement include; the use of bearings to reduce friction, waxing the wood where it rubs together, or replacing/coating the wood with a layer of Teflon which would greatly reduce friction and help with the air seal. You might also try making the air input/output holes a little bigger and upping the PSI for more speed.
If you have any comments, questions, or suggestions please don't hesitate to put them in the comments. I'll do my best to respond to them.
I hope you enjoyed my instructable and I wish you a successful build.