Introduction: Soup Can Savonius
Here’s my first venture into writing an instructable. I’m not creating much new here, just giving people a cheap first step into making Savonius styled wind turbines and trying out some new ideas. Most of the materials can be found right in your own garage if yours is as filled with junk like mine.
Step 1: Getting Started
Parts to buy or have laying around:
2 Glass sliding door wheels– purchased at Menard’s for about $3
6 Magnets – need to be N and S poled. Purchased mine cheap (about $.60 ea. from Menard’s) Rare
Earth magnets would have been better but I’m cheap.
¼” threaded rod about 24-36” long (depending on your soup can height)
¼” hardware including washers, lock washers and nuts
Clear silicone sealant or epoxy or resin or glue, etc.
Probably have laying around:
2 same sized empty soup cans
Rulers, tape measures etc.
Jig saw, scroll saw or band saw
Drill or drill press
1/4" –3/8” plywood X 3 disks– Thicker would be fine except very heavy. Thinner would be fine except for the bottom layer. Most soup cans will have a finished turbine diameter of less than 8 inches.
Misc. screws, string and other scrap wood for framing and other last minute MacGuyvering.
Glues of various sorts.
Step 1 – Soup is Served
Eat some soup! Just about any sized can will do. The bigger the better. The cans I used were from some large tomato soup. The were about 4” diameter and maybe 6.5” tall. Measure yours. It’s best if it doesn’t have the rounded bottom as it makes it hard to cut off. With a regular bottom, you should be able to just use the can opener on the bottom. Once it’s all cleaned out, place it on a blank sheet of paper. Trace a circle around the base and place soup can to the side. Fold resulting circle in half and mark where the fold line meets the edge of the circle.
Place soup can back over traced circle and mark where you marked the half folds. It’s easiest if the soup can already has a line on it from the manufacture (seam line). Mark top and bottom and use a ruler to connect the marks. Use tin snips to cut can in half. Be careful since sheet metal edges are razor sharp. Best to use leather gloves for this part.
You should now have two soup cans cut in half now. I chose to run the grinder on the edges to make them slightly less sharp but that is optional. You can also tape them by folding some duct tape over the edges. As mentioned before, sheet metal is very sharp and should be handled with care and leather gloves.
Step 2: Some Math… AHHHHHHHHHHHH!!!
Time for some math. As long as you’ve had algebra, most of this should make sense. If not, use a calculator and skip to the final portion of step 2.
If Y=Ending diameter and X=Soup can diameter, Y=2X-.187Y. This comes from some research and other instructables that I’ve read that say the overlap should equal 18.7% of the total diameter.
Therefore: Y=2X / 1.187
Or in layman’s terms multiply the diameter of the soup can your using by 2. Then divide that number by 1.187. This should get you the diameter of your plywood circles you need to cut.
Step 3: Cutting Some Wood
There are a couple options here. (1) You can put a screw in the wood and make a string round a pencil the length of your radius and make your circle on your plywood that way. (2) I used a scrap piece of 1x2 and drilled a screw clearance hole about an inch in from the end. Then measured the radius and drilled a hole centered on the radius for a pencil to fit. Then I partially screwed through the clearance hole into the plywood and traced my circle. I found it to be nicer than the pencil and string for many reasons but mainly the pencil was kept at same angle since it was sized to the hole and not able to angle it like the string method. The other thing that I really liked was that it was easier to get a more precise diameter since I didn’t have to worry about string stretch or tying a perfect knot etc. You will need 3 discs of wood.
Once you have your circles drawn, cut them out with a jig saw or scroll saw or band saw etc. Draw a nice straight line across them through that nice screw hole in the middle. Mark one of each; top, bottom and middle. The middle should have a line on each side, 90deg. from each other. Draw the one line on one side. Draw transfer lines on the side of the wood and draw same line on other side. Then use that to draw another perpendicular. Cross out the transfer lines so you don’t get confused.
Step 4: Layout
Time to trace the soup cans again. This might get a little tricky. Lines on top and bottom of one section should be mirror images of each other. Make sure that in the middle, the soup cans are catching wind in the same direction, just rotated 90 degrees from each other. It’s easiest to start by tracing the bottom, then placing the middle on top of the soup cans so that you get started on that tracing right. If you can wrap your head around it without physically doing it that’s great. I traced inside and out of can. I only used one can for it all.
Step 5: Bring in Reinforcements!
For strength on larger cans, you should make a small groove on your newly traced can lines for your cans to sit into. You can instead add a thin layer of some cheap 1/8” plywood or chipboard etc. cut out where the cans go x 4 for all surfaces the cans touch. I was using thicker plywood since that’s what I had so I cut grooves. This may be unnecessary, but I tend to overbuild things.
Center holes. Drill a clearance hole on all the disks for the threaded rod your using. The smaller the threaded rod the better the airflow through the overlap. There is a purpose to the 18.7% overlap. That is so as the wind pushes on the facing can, some of the air flows through the overlap and pushes back on the other can, adding power and compensating slightly for the wind pushing on the back side of the other can.
Time for the glue. I used Gorilla Glue since it’s expanding and strong for a wide range of materials and I had it laying around. If using Gorilla Glue, probably need some water spritzed on the cans since they’re not porous. You can tack some short finish nails at an angle through the cans or some small screws. Might need to punch a hole before nailing to finished product. Let glue dry for as long as it says on the bottle.
Step 6: Bearings
I’m using the wheels from glass sliding doors (closet doors). I was able to find only at Menard’s, separate wheels. The ones at Depot were attached to something so that’s why I say Menard’s. I got the 1-1/2” ones. The center hole of those is perfect for ¼” threaded rod. That’s the reason for the ¼” threaded rod too.
Now you need to figure out your base materials and sizes. I had to replace a disc brake rotor on my truck a while back and the old one was still sitting in the garage. It’s nice and heavy and has nice predrilled mounting holes. It has a large hole in the center which you will understand later. I’m sure your local auto parts place or tire place etc. will be fine parting with some used unturnable ones. Or you can use a block of wood or blah…blah…blah.
To this I’ll be attaching a scrap piece of 2x10 pine from a bed frame I built. The depth of 2 inches is good for the bearing fitting and the weight helps too. The more stable your turbine is the less chance of it tipping over. Especially weight on the bottom. In that piece of 2x(whatever you use) drill a hole for the bearing outside diameter, in the case of my materials it’s a 1-1/2” hole. Drill it the depth of the bearing plus about a ½ to ¾ inch. Then drill a hole in the center all the way through so that the inside of the bearing, the bottom washer and nut and the threaded don’t ride on the wood and so that the threaded rod can pass through below the wood unhindered. The outside of the bearing can be held in by a layer of Gorilla Glue or some well placed screws drilled through the outer edge of the wheel. If you’re using another type of bearing without a wheel, you probably can’t drill a hole through the outside without screwing up the bearing.
Step 7: Decision Time
If you don’t want to put magnets to your turbine until you make a bigger one, skip the explanation of magnet/coil placement. If you do want to make power with this, how many coils do you want? What materials do you want to use for vertical supports? What scraps do you have laying around for verticals or for the top plate?
The vertical supports. These are what tie the bottom bearing housing material to the top bearing housing material. The verticals are decided on a few things. If you’re worried about airflow in multiple directions, is this something just to show people with a house fan demo, is this going to see high wind speeds, am I experimenting with some ideas that I might want to use in a larger turbine and so need to test some things in various wind conditions, etc.? All these effect if you can scrounge the parts or need to spend a couple bucks at the home center. I have some 3/4” dowels laying around so I’ll use 4 dowel supports. I want to try mine out in some wind around here near the windy city (though it’s not named that for it’s actual wind speeds) so I need something sturdy but not to obstructive. Other options may include angle iron, other scrap wood, metal round stock, pipe with flanges for mounting, etc. Decide a length that suits your turbine. Your bottom spacing should be 1/8” or less between the magnets and the coils. The top should be spaced at least 3”-4” for adjustment purposes. See the mounting procedures for more info. Do not put frame together yet. Leave top bearing housing separate for now.
Step 8: Coil Design
Coils and magnets should be about the same size. Since I have small round magnets I’ll have small round coils about the same diameter and not too deep since my magnets for this are just sucky ones for the home center. I’ll be using cheap plastic bobbins from a sewing machine. Something like $.75 for 4 from Wal-Mart. I’ll be winding them on the sewing machine in the bobbin winder. Radioshack doesn’t carry a great selection of enamel coated magnet wire but it will have to do for now. They carry a 3-pack of 3 different sizes (24, 28 and 30 awg). I think the longest length is 200 feet for the 30 awg. Not much for doing a lot of coils so go to the internet for getting larger lengths of one size. From what I’ve gathered, any of those sizes above should work ok. The more coils closer to the magnet the better. Make sure to mark your inner coil wire and outer coil wire if your making this a multi-coil turbine.
The coils are going to be inset on mine into the base 2x10. The magnets are going to be set into the bottom of the turbine. That way with higher winds there aren’t sharp edges to catch if the turbine starts to wobble on the bearings. Figure out a nice radius away from center that doesn’t interfere with any mounting or cans and is far out enough to fit the 6 magnets (or however many you have). Mark this on both the base and the bottom of the bottom of the turbine. Mark 6 evenly spaced spots for the magnets and mark however many evenly spaced coils you chose. This can be done similar to finding the half of the circle. Trace a circle on a paper to match the diameter your using for your magnets. Then fold circle in half and then in half again. This will give you a center. Use a protractor if you’re using 6 magnets to mark 60 degree marks on the outside of the circle. Then center this paper on your bottom bearing housing and use a nail to make a dot to match the marks you just made. Do the same for the bottom of the turbine.
On mine there will be 3 coils for each of the different wire sizes I have so I can see if there is much difference between them. Choose a drill bit slightly larger than the magnets and the coils, which should be close to the same size. Drill holes into the base and bottom turbine disk just deep enough for the coil/magnet respectively. For the coils you might want to take a dremel, circular saw or table saw and cut some shallow grooves for the wires. You can also have them punch out the bottom of the coil hole just be sure to mark them.
The coils and the magnets have to be as close as possible since I think there is an inverse square relationship to the distance apart. Meaning the farther apart they are the weakness grows quickly. So set them in their holes and shim them to get them as close to flush as possible. Than silicone or epoxy or whatever them in place so they don’t move and so the surface is flush.
Step 9: Mounting
Mount that 2xwhatever to your brake drum or block of wood etc. Make sure you countersink your mounting hardware since raised hardware will make it tougher to get your 1/8” or less clearance.
Place threaded rod through clearance holes in the turbine. Place a washer, lock washer and nut (in that order) on the top and bottom of the turbine and tighten slightly. Don’t bust your turbine glue joints cause you think you’re the hulk. Then on the bottom and top place (in order) a nut and a washer.
Set threaded rod through bottom bearing. Place top bearing housing on top of whole shebang and fasten to verticals. Now time for height adjustments. As long as you have a few inches between the top of the turbine and the top bearing housing, you can easily make adjustments to the magnet spacing. Simply lift rotor a couple inches and move the last nut up or down. When you’ve finalized your spacing, place a washer, lock washer and nut on the threaded rod sticking through the top and bottom of the assembly. So for final assembly it should go from top to bottom on the threaded rod: nut, lock washer, washer, top bearing, washer, nut, nut, lock washer, washer, turbine, washer, nut, nut, washer, bottom bearing, washer, lock washer, nut.
Step 10: Final Thoughts
Now place in windy area or in front of fan and see what you get for a voltage output. You can adjust your height to see if that changes things drastically. To do so, just loosen the nut under the top bearing, loosen the nut under the bottom bearing and slide the whole thing up (remember the few inches above the turbine), adjust the nut on top the bottom bearing to where you want it and then slide it all back in place and tighten it all.
Some final tidbits. If this is going outside, might want to clear coat it with some outside varnish. If your turbine is too heavy, drill some holes in the plywood disks but don’t make it too lopsided. Experiment with different ideas and comment about it so others can learn freely from your challenges. Mine needed some greasing of the bearings. I soaked it with WD-40 (I know it’s not a lubricant) and it seems to work.
“While one person hesitates because he feels inferior, the other is busy making mistakes and becoming superior” – Henry C. Link
There are other instructables on Savonius (search “savonius”) wind turbines that have explanations of 3-phase power vs. single phase as well as instructions for larger turbines. There are also various other Vertical Axis Wind Turbine designs out there too including an instructable on the Lenz 2 Turbine and another website for an involute spiral design (http://www.stiltman.com/html/wind_power.html). This is just a starter and a tester. My next savonius turbine will be built out of the water heater skin I just tore apart in my garage. Hopefully you and I have learned some things from constructing this simplified model that we can use to build more complex or at least larger versions. I haven’t hooked the coils up yet to test voltage of the cheap magnets. I figure if the cheap ones don’t work I can always flip the turbine part over and put good magnets on the other side.