Experimental Savonius Rotor Experiment:
By jimpep, Section Wind Posted on Sat Jun 25, 2005 at 06:04:22 PM MST
I am looking for feedback on my VAWT experiment.

Over the last year I constructed a VAWT saronius rotor with the hope of improving efficiency with slight design changes. I constructed it completely with sweet equity and scrap metal from my workplace with the exception of bearings, paint and wire to this point. The rotor is made of oil barrels cut in half. I started using jig saw blades but ended up using a plasma cutter to save time. I also cut away all but ~3/4" of the barrel ends because I have no center shaft. I did this because what written stuff I have seen points to lower Cp because having a shaft blocks the airflow through the center. I used 4 stages of 2 barrels halves to maintain suggested configurations of a Dr. Modi.They are set at 45 degree offsets. The dividers and made of ~20 gauge ss cut out with a plasma cutter. I read that the dividers should be 5% larger then the laid out barrels which was ~44" with an 8" overlap in center for air flow. In the building process I decided to cut the trailing ~6.5" of barrel which I bent to give a more aerodynamic shape. At this point I welded my first 2 sections which I then realized spanned the whole divider since I had now stretched it out some. The next 3 dividers were then resized 5% larger then the original 2 dividers. ( Obtaining scrap stuff is kind of like sharks in the water...hit or miss...who ever gets there first.) The effect of this is to have 3 larger top sections dividers.This slightly tapers the bottom section down. The bottom/top dividers have bearing mount plates installed. The top for a good feeling sedan spindle/bearing and the bottom for a 95 grand am drive spindle/bearing . I then cut the drive shaft off with cut off wheels so I could insert the splined shaft through the spindle bearing which goes through the plate for my electrical rotor attachment. I made templates for the bearing plates by taping out the splined lug nut studs for accurate transfer punching. I later reinserted the studs when it was time to attach it to the mounted bearings in the tower. I then welded and drilled out the end dividers . The tower is 21' pallet racks, 5' of which is in the ground with welded piped cris crossing in all directions for support. One side is slightly lower which has caused me to shim the bearing mounts so that they were level. The completed rotor was just under 12' long and ~44" wide. After mounting the rotor I let her freewheel. To my horror (and delight to know it turned) in a ~15 MPH wind, it freewheeled apparently out of control and bent in the middle sending periodic sparks in the darkness in faster gusts of wind.  The center stage divider had worn a ½" slot in the tower by the time I stopped the rotor. I then locked it down and over the course of a couple of months added 4 - 1x1 square stock bars to give it support. I did the best I could to balance it by welding on pieces of stainless flat stock. Usually I leave it locked down but on some days with winds below expected 20 MPH winds I let it freewheel but in general do let it exceed ~210 RPM at (~20 MPH) which time it starts to cause tower vibrations. I left 2 sides open for more free air but I think I am going to add at least 4 more cross pieces to strengthen the tower and cut vibration hopefully at faster speeds. My company uses magnet canisters in its food safety program and when they don't reach a certain pull test they are discarded. Guess what they are...Neo(S) abet on the small size. My electrical rotor plate is just over 23" in diameter of ½" thick steel cold rolled plating and I am using 40 discarded 15/16" dia by 7/8" high neos. I have 17 others of the same size. I also have a few dozen more of larger and small sized neos. I have tinkered with only 3 coil designs. One was with lengthwise coils which didn't work to well. Then I tried a spool which did a little better and then I did a round coil which is the best so far. I am testing 21 gauge wire starting with an ID of 3/4" out to over an inch. 68 ohms of wire. I developed an unacceptable 1.25 Volts ac @100 rpm on 1 coil but I can obviously increase my turns to get more voltage and improve the shape. I can also make an extension and have a dual rotor which I am leaning towards. ........so here goes the questions : ) Coil spacing should be the size of the magnet. What kind of problems can be made by squeezing in a few more coils or overlapping coils ? ) Do I have to keep the magnet spacing the same diameter as the magnets or can I take extra neos and squeeze them into the circle or does cancellation negate any benefits ? ) How much would I lose if instead of a dual rotor I doubled up on my magnets on the single rotor and put laminations on the stator ? ) Would it be economically worth it to scrap my smaller neos and install larger ones. ) Any other comments to help me pull as much out of this project as possible. It may me that it will just be a property ornament and staging for a Darius Experiment or HAWT on top of the tower. My neighbor asks "what's that twirlly thing in your field ? " Thanks Jim from Vermont

Experimental Savonius Rotor Experiment: | 20 comments (20 topical)

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#1) by Norm on Sat Jun 25, 2005 at 12:37:12 PM MST

I rhink you would have been better off with a center shaft  I don't think a shaft would make it that less efficient.  A large disk brake the same size as one of your disks should stop it easily.  A power take-off pulley and you could be doing useful work while you are building an alternator for it...would be fun to watch it lift a heavy weight to see how much torque it had...you could collect some data to figure what size alternator that you could couple efficiently to it....               What a neat little 'toy' ....wish I had the location like you have for one of those!                 ( :>) Norm. ( :>) Norm

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#2) by Nando on Sat Jun 25, 2005 at 01:35:43 PM MST

REPAIR the mill, INSTALL a strong shaft. Make sure that the shaft is truly centered to the barrels At the base install a 2 inch thick 24 inch wheel, using the wind give it a groove for a belt to have ways to experiment. Coil resistance is too great, I will let those have have played a lot with magnets and axial generators to give you a good guide. Nando .

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#3) by hvirtane on Sat Jun 25, 2005 at 01:57:57 PM MST

Looks nice. I hope that you will get it fixed soon. I think that you can do without any belt drive for the generator, if you'll make the diameter of the magnet disks really big. You might use for them rims of a farming machine, for example. - Hannu

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#12) by jimpep on Sun Jun 26, 2005 at 04:51:35 PM MST

That was the original intent. I was going to make the mag/rotor so large that I might not need any belts for gearing and hence no power loss to friction ETC. Thanks Jim [ Parent ]

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#4) by georgeodjungle on Sat Jun 25, 2005 at 02:38:06 PM MST

to cool, and a nice niegbor. paint it up like flag just in case. looks like you have about 30 sq foot of swept area. i could feel the power from here. so will say 20 just for fun. i'd say with the right pulleys or cogs you could get an 800+ watt to smoke at 10 to 15 mph. less friction & bla bla bla. some way to stop it would be goog  but all that work you got in it now. got to get more power out of it jim ! sorry i couln't resist.

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#9) by jimpep on Sun Jun 26, 2005 at 01:38:55 PM MST

Thanks for the input. 800+ watts would be excellent. My coil making is in the infant stages so I will not draw any conclusions yet. Jim [ Parent ]

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#5) by veewee77 on Sat Jun 25, 2005 at 02:43:54 PM MST

15/16"x7/8" isn't really a "small" neo magnet!  If you do decide to replace them with larger ones, I'll take those old ones! Looks good, though.  Balance is going to be very tricky on it though. Since it is in 4 sections, I would assemble each section and balance that section individually, and then bolt the sections together and balance the whole thing. The whole thing could be balanced as a whole but each section in itself could be out of balance and cause vibration once it is rotating. I have been thinking about doing a similar (but smaller) version with 5 gallon buckets. Doug

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#6) by veewee77 on Sat Jun 25, 2005 at 02:46:35 PM MST

P.S. Put in the shaft, too. . . It'll be sturdier. . . and there won't be much measurable effect anyway. [ Parent ]

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#7) by wildbill hickup on Sun Jun 26, 2005 at 04:22:04 AM MST

Jim, WOW, Nice machine, usually when I read one of these posts I look for the pictures first, then I go back up and read the post. When I saw the first photo I thought, I've seen that somewhere, and low and behold at the bottom of your text there it is, your in Vermont. I live in the Northeast Kingdom, Sutton actually and I swear I've seen your machine somewhere. Where are you? Email me if you wish. Just a few thoughts (not that I'm any expert) First like others have said, judging by the size I think a center shaft is a must and won't affect air flow that much. On your rotor it looks like you have plenty of room for more magnets, if you could collect enough of the same size for 40 more (23, You said you had 17) you could place them just inside the exsisting ones (aligned on the angle spoke the same, but closer to the center) and make a bigger magnet then wind your coils twice the size(or the same number of turns with bigger wire) in an oval shape. You could even use the smaller magnets to taper this 'bigger' magnet down towards the center, and make your coils even bigger (in a wedge shape). I would recomend that each set of magnets be the same size though(for balance mostly)  In any case larger wire is needed and if the 'big magnets'(made up of sets of 40 progressivly smaller magnets) is longer you can use more turns of wire in each coil. Or you could use sets of 40 of the smaller magnets you have and put a second and or third 'phase' of magnets on the rotor and coils in the stator progesivly closer to the center, on each spoke. I hope that makes sense. That might keep you from haveing to use tree trunk size wire for your outputs, It would be like having 2 or 3 altinators in one(each producing 1/2 or 1/3 of a total output). The wiring and phase guys could give you more exact info on this than I can. Just my two cents, and I love to see that up close and for real, again nice work, you have the potentail for a real powerhouse there. Wildbill

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#13) by jimpep on Sun Jun 26, 2005 at 05:02:54 PM MST

Hi Wildbill: I live in Georgia Vermont. Maybe the rotor you remember was between Johnson and Jeffersonville Vermont. It is a dual- 6 stage unit that I used to watch spin as a kid on trips between Burlington and Newport.It no longer turns because the dividers were made of plywood and the metal is all rusted away. If you look closely in the first picture you can see the edge of 100 sq feet of used solar panels that I got in Barre for $800.total.( 4 panels) The system has been working great. Let me know if you want to come up and I will leave directions. Jim [ Parent ]

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#15) by wildbill hickup on Sun Jun 26, 2005 at 08:44:23 PM MST

Georgia it does sound somewhat familiar but I can't place it. I looked on yahoo maps and niether have they. The zipcode listing in the phone book doesn't even list it. Must be a big town :->. Not surprizing though I lived in this area for 10 years before I learned of a village that's actually part of East Burke called Texas. I guess you'd better give directions. I really would like to take a for real look at your creation one of these days. Do you know where Sutton is? Near Lyndonville? Since I have no idea where I'm going you might as well give directions from Lyndonville. You can post here or email me if you prefer that, a phone # might be good too so we can discuss dates and times. Wildbill [ Parent ]

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#19) by jimpep on Tue Jun 28, 2005 at 03:25:36 AM MST

I have a sister in East Burke and some of my wifes more distant relatives settled in the Wheelock/Sutton areas if I remember right. Georgia is South of Saint Albans, North of Milton and West of Fairfax. Give me a shout at jkpep@msn.com if you want to come over and take a look. Jim [ Parent ]

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#8) by zubbly on Sun Jun 26, 2005 at 04:30:34 AM MST

Hi Jimpep! I often wanted to try making one of those myself, perhaps some day i will. But here is my 2 cents worth. If you do use a new shaft from one end to the other as some here have suggested, it will provide you with an excellent way to balance the unit. Once the shaft is installed, i would suggest mounting the unit horizontaly on 2 V blocks (one one each end). This will allow the unit to find its own heavy spot and should greatly increase your chances of a good balance. The most accurate way is to balance each section at a time as you really need a 2 plane balance because of the length to width ratio, so mounting one section, balance it, then add the next section, balance it and so on will give you each section statically balance. Its a good way to do it when the equipment for a 2 plane balance is not available. hope this helps ya!  have fun  :) zubbly

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#10) by jimpep on Sun Jun 26, 2005 at 01:49:05 PM MST

I kind of did this.When the rotor was on the ground I installed the 2 end bearing and plates and raised the whole thing a few inches off the ground. I spun it around and welded balance pieces on so that it would never stop in the same place. It went fairly well. I think a drawback is that a 4 stages rotor is just a pain to balance. In the rotors vertical state it never stops at the same spot which may or may not be related to its total weight. Thanks Jim [ Parent ]

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#11) by jimpep on Sun Jun 26, 2005 at 04:45:27 PM MST

The barrel halves are all welded and heavily spot welded to the dividers and the 4- 1x1 bars are all welded into the 1x1 slots into the dividers. Everything is quite sturdy. I don't think adding a center shaft at this point will add much to the structure. If I cut all of the barrels away it would ruin barrels and damage the dividers. Hence I would have to start from scratch.Everything is triple primed and triple painted except the bars. At this point I want to set up the PMA to start making some power with the rotor I have constucted. Thanks Jim

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#14) by jimpep on Sun Jun 26, 2005 at 05:20:12 PM MST

Well I think 210 RPM is whipping for this rotor. I really want to load it to slow it down. I think one of the reasons it starts to vibrate at that speed is the way I bent the barrel's trailing edges down into a more aerodynamic shape.I didn't have a torch so I bent them this way. First I poured a 22 OZ homebrew. I then stepped lightly onto the barrel halve and using the beer as a counterweight for balance I pushed my weight onto the barrel bending the edges that I had cut. After bending 2 barrels halves I would then drink the beer. Even though they are all welded at the same spot I think there is a slight difference in the shape. Below is a picture of the not fully carbonated cousin of the same homebrew I was using last fall. Jim

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#16) by DBGenerator on Mon Jun 27, 2005 at 10:21:50 AM MST

I like it.  It might be cool if you could paint something artistic on it.  Maybe an add for Mail Pouch tobacco.  That's a joke.  Actually, you should send it to the oil companies.  You found something more worth while to do with the 55gallon drums instead of wasting the drums on the overpriced oil.  Get them to produce more energy there as a wind turbine than if they were filled with oil. As far as your magnets and coils, I think you could probably fit a few more magnets on there and the size of them is big enough to produce enough electricity.  Definately worth using.  The center diameter of the coil should be the same as the outer diameter of the magnet.  I'll try to attached an image that someone posted earlier here... Dave

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#18) by jimpep on Tue Jun 28, 2005 at 03:19:38 AM MST

I actually thought of painting something that would appear to move at a certain rpm. Runner joging, fish swimming or maybe just colors. Back to the PMA.... The magnets diameters are the same size as the spacing. If I add more magnets then I am violating the "ID of the coil should be the OD of the magnet rule" ? At the least I would have to elongate or make my coils smaller if I add more magnets and if I understand things right. Why does a coil ID have to be the size of the magnet ? Why can't the coil ID be 1/4" to conserve space ? This would allow for more windings and hence more voltage ? Notice I have one spare neo toggled up against one of my other neos for more BR. I haven't explored that yet either. I also have thought of adding my larger Neos on the plate which would mean a multilevel stator but it would be nice to iron out the base 40 neos first. I was hoping for some input from some PMA experts : Windstuff ED, ECT. Thanks Jim [ Parent ]

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#20) by kitno455 on Tue Jun 28, 2005 at 07:14:34 AM MST

Jim, consensus seems to be that you dont want both legs (sides) of the coil over the same mag at the same time, cause they will cancel. if you try to cram alot of small coils in there, you will get just that, and be wasting alot of the wire. now, that said, because the coil legs have width, it is not actually possible to make the coil the optimum size, most folks seem to shoot for the average lap of the coil to be the same size as the mag, others like the hole in the coil that size. the coil size is also related to the spacing to the next mag. try to get the average lap to hit the next mag, just as it's back leg is leaving. this implies that there is a relationship between the spacing of the mags and the mag size as well. but, when you have the option, multi-phase machines will work better. that also changes the relationship, but generally in an easier way, by making less coils, which helps with the fact that they have a finite thickness. i think danb puts his mags a bit closer, to try and get more flux in the space. i agree with others who have said to get a second ring of mags inside the first, or switch to bar mags on the lower rotor, and move the second ring of rounds to the top. be very careful with the truing on these rotors if they get very large, they will tend to become floppy with all the mag pulling on the edge. some strengthening ribs welded to the back maybe? allan [ Parent ]

Re: Experimental Savonius Rotor Experiment: (3.00 / 0) (#17) by DBGenerator on Mon Jun 27, 2005 at 12:44:05 PM MST

Here is the image.......

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