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Forum Index : Windmills : VAWT Idea - input wanted
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| skgtheblij Newbie  Joined: 14/10/2011 Location: EthiopiaPosts: 8 |
Hello, I am currently working on an idea for a VAWT, and I think i'm stalled. I would just like to throw it out there to see if i'm missing something before I give up on it. If someone can provide input towards the issues I have with it, I may build it, but as of now, I'm not planning on it. The basic idea is a pivoting sail, which on one side is perpendicular to the wind, and on the other side rotates to be parallel with the wind in order to reduce resistance. The idea is that torque would be produced even in low wind. The biggest issue I am having right now though is harvesting that torque in a useful manner. The design which I am basing my calculations on has 3 4 meter high 6 meter long sails. So given a 5 MPH wind, and assuming that the system rotates such that the tip moves at exactly 5 mph, that is less than 4 RPM, which is EXTREMELY slow. But it should be generating a theoretical 181 N-m of torque (133 ft-lbs)(or with a 15 MPH wind, 10 RPM and 1600 N-m) 
This is a mockup of the windmill. In this image, the wind is coming towards the viewpoint, offset to the right a little bit. Two of the sails are tracking directly into the wind, while the third is perpendicular to the wind, driving the assembly in a clockwise direction. The problem I have is that I can't think of a way to efficiently harness this power. I could use a transmission system with an enormous gear ratio, but I'm not sure how to build one and I think I would lose a lot of power. I was originally thinking of buying a Missouri Wind and Solar PMA, but I don't think that even with a huge RPM up-conversion that it would be practical. The site where I would build this has usually 5-15 mph winds. Any input/insight whatsoever is highly appreciated! This is a good learning experience for me regardless of whether or not I decide to go through with it. |
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| electrondady1 Senior Member  Joined: 12/02/2009 Location: CanadaPosts: 208 |
remember when you put a load on the mill it will slow down yours is a different animal than what's typical but for a loaded drag mill a tip speed of .6-.8 of wind speed is considered ideal you could harness the torque for the same thing they have done with verticals since the dawn of civilization. grinding grain, sawing wood, pumping water. electricity? dc motors are as common as dirt. put a wheel on the shaft of the motor you could just set one up on the circumference and let it spin. not sure if all that was helpful or not. |
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Tinker Guru  Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
From your description I cannot follow how this arrangement is supposed to work. Perhaps if you describe a compete cycle of what the 3 sails? do and what happens to the central shaft (simply rotates or what?) during that cycle. If your mock up could be animated it would be a big help. Klaus |
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| electrondady1 Senior Member Joined: 12/02/2009 Location: CanadaPosts: 208 |
the down wind side presents its full width to the wind the up wind side rotates to present a reduced profile to the wind. this reduces the energy required to drag the next sail into a position were it can harvest. |
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| skgtheblij Newbie Joined: 14/10/2011 Location: EthiopiaPosts: 8 |
Thanks for the replies. First, a reply to Electron. Attaching a motor to the circumference is a great idea that I had not thought of, and I appreciate it. (in fact I could attach a couple DC motors) but the issue is that the device does not have a constant (or even circular) circumference as the sails are always rotating. My initial idea was to attach a 1 m wheel at the bottom and use it as a pulley to drive a Missouri Wind and Solar PMA, but with a 1 m wheel and a 10 cm pulley, that is only a factor of 10 and would only give me 30 RPM (using your ideal tip speed)Do you know of a DC motor that would produce useful power at such low RPMs? The issue here is that if i'm going to build it I will go all out, and it will be kind of expensive. I really want to have a solid plan for power generation before I commit. And Tinker, it's a little tough to explain but Electron has it right. A complete cycle of the three sails, starting from how it is in the image (and letting the sails be A, B, and C from right to left) would be: 1. as it is in the image; the C sail is perpendicular to the wind and is driving the assembly in a clockwise direction because the frame of the sail is pressing against the arm of the assembly. A and B sails point directly into the wind because they are attached offset from the center of the sail, like the tail of a windvane. 2. B sail rotates to a point where it can no longer track the wind as its frame is in contact with the arm of the assembly. C sail is still driving the assembly, and A sail is still freely following the wind. 3. C sail reaches a point where it is just beyond perpendicular to the direction of the wind, and the wind is blowing on the backside of the sail. It does a 180 degree rotation about its pivot, and the edge which was closer to the inside is now on the outside, and it is again perpendicular to the wind, leading into the wind with it's shorter edge. B sail is now driving, and A and C are tracking the wind. 4. The A sail can no longer freely rotate, and it is helping the B sail drive. 5. The B sail goes beyond the 180, and does it's 180 degree pivot, and begins tracking the wind. A sail is driving. etc etc. I hope you get the idea. Thanks again for the help! |
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| skgtheblij Newbie Joined: 14/10/2011 Location: EthiopiaPosts: 8 |
What if I were to use a gearmotor like this: http://www.ebay.com/itm/6-RPM-12-VOLT-DC-HIGH-TORQUE-INLINE- GEARMOTOR-5-1748-/270685929761?pt=LH_DefaultDomain_0&hash=it em3f06238121#ht_1578wt_1037 Do you think I would see decent results? Also, how would I calculate the torque necessary to turn the thing, and what my power output would be? Thanks! |
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| Air Bender Senior Member Joined: 25/01/2011 Location: AustraliaPosts: 206 |
Hi skgtheblij, I can see the main problem in your design being the part of the rotation where it does its 180 degree pivot, in sailing terms this is called a gybe, it is when you turn the stern of the boat through the wind and the boom crashes from one side to the other it can be very damaging if not handled well. It may work if you can dampen this 180 degree swing down a bit or cushion it somehow. Maybe we can harness the force of the gybe for making power. All the best Dean. |
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| skgtheblij Newbie Joined: 14/10/2011 Location: EthiopiaPosts: 8 |
Thanks Dean I hadn't even really considered this as a problem. I suppose my plan would be to cushion the gybe, as I was planning on having as low friction as possible in that joint in order to reduce friction during the wind following stage. Perhaps something similar to the device which keeps a screen door from slamming but causes little resistance for small adjustments? Theoretically, the gybe-ing sail might not hit anything, as it would pivot only until it is pointing directly into the wind, but realistically its moment of inertia could carry it beyond that point and cause it to slam into the front. |
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| Air Bender Senior Member Joined: 25/01/2011 Location: AustraliaPosts: 206 |
Hi skgtheblij, I think if you have the pivot point on the front of the sail and not part way back it may swing around without hitting anything but if you have anythig in front of the pivot it will slam into the rotor arm. You will find that when it swings around it will swing around with a lot of force. Maybe this extra force could be harnessed like a turbo boost using hydrolic or air pistons. you could have your stator conected to the pole and the rotor conected on the spinning mill but sped up by the extra force of the gybe. I am on a long night shift at the moment and my mind tends to become a bit overactive. All the best Dean. |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Yes, I see how it works now, the vanes (sails) are individually pivoting. I should think it might make a noisy wind mill if you let the sail gybe freely. Even if it does not hit something there will be a 'whoosh' as it flips over. Perhaps some shaft friction dampener might reduce that. The other thing is there would be a jerk on the shaft each time sail flips over so this thing might not have a smooth drive on the alternator shaft. As you say, keeping the revs as low as practical sounds a good idea. Klaus |
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| skgtheblij Newbie Joined: 14/10/2011 Location: EthiopiaPosts: 8 |
Thanks again for the input. Bender, your idea of putting the hinge all the way out is a good one. My only concern is the moment on the joint to the shaft gets significantly bigger. However, I think that will be okay because I can join all the arms to the shaft at the top as well, and they can pull off each other. I'm working on modifying my model now. Tinker, sound isn't so much of a concern, but you're right that there will be a jerk on the shaft. That will be something i'll need to work on. I think that my motor(s) will hang off the end of the driveshaft and be loosely connected in such a way that the stators can't spin (but can move up/down, side to side a little) My new burning question is with these DC motors how to charge a battery bank. Do I need a charge controller? And charge would only happen above 12v (for a 12v battery) right? Caleb |
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| electrondady1 Senior Member Joined: 12/02/2009 Location: CanadaPosts: 208 |
there is an old expression killing two birds with one stone. adding a large diameter ring to the base of the mill, and using that as a platform to locate and strengthen the pivot points for all three wings , will also provide a large diameter drive wheel for any dc motor you place on it. |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Caleb, I had some thoughts about your 'flip wings' today, being a sailor the following suggestion comes to mind: 1. make the 'flip' pivot location adjustable on your model. Start with a location as close to the center of the wing area as possible and still get reliable 'flip' over. Doing that makes the area of the downwind heading part just slightly larger as the one heading upwind and the upwind going area dampens the whole process. Gybing the sail on my yacht can be violent as its hinged right at the mast. Older type rigs (like junk rig sails) have part of the sail forward of the mast and gybing these is much more gentle. 2. charging, Wind generators require a load at all times so any charge controller you use would have a provision to connect the whole output to a dump load (a heating coil capable to absorb the windmill's storm output without burning out). 12V batteries require around 14V to charge so your DC motor must be able to output that at anticipated RPM. The controller senses when the battery is full and then switches over to dump load. Klaus |
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| skgtheblij Newbie Joined: 14/10/2011 Location: EthiopiaPosts: 8 |
Many thanks to those of you who replied. Tinker and Bender both have very different but good ideas on how to deal with the Gybe problem. Bender says move it to the end, so however violent it can't damage anything, and I was considering making the system taller and skinnier and doing just that until I read Tinker's comment, which is to move the pivot closer to centre, an idea which I think I actually prefer. And Electron, your idea is also brilliant, and it would kill two birds with one stone. My main hesitation with that would be making the ring, as I don't have that great of a shop. I'll definitely be looking into it though. I think I plan on using this gearmotor from surplus center. I will then buy a couple different sized pulleys from the same place to test out different RPM loads. And i'll buy a charge controller as well. Thanks for all the help! Caleb |
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Oscar4u Regular Member  Joined: 23/02/2011 Location: New ZealandPosts: 42 |
Hello Caleb a most unusual design! I do not completely understand it. Three sails? They are equally spaced, ie 120 degrees apart? each sail can pivot on its mount? how will you regulate this pivoting? my experience is only with waterpumps but am very cautious of the idea of the idea of having pivoting blades. To make a design that works is one thing. To make a design that gives you trouble free motoring for ten years is another. When eventually I make a power generating windmill I will try to design something that will give trouble free motoring. My suggestion is to rather make something less efficient but larger. Having said that your suggested size is fairly substantial as it is. Because you have such a slow speed i think it would not be that difficult to make a flat pulley to power your generator with a v belt. It should not be too difficult too make a two meter or larger diameter flat belt. Because you would not get it perfectly round, you will need a tensioner or to spring load the generator. This is possible but vee belts are notorius for robbing an appliance of power. If I were to do something like that i would use a gearbox running very light oil. If you used a second hand car gear box you could change gears and experiment which ratio is ideal. I suspect a car gearbox is not the most efficient but they are very plentifull and cheap. That 6 rpm gearmotor you are looking at is rated intermitant use. I am suggesting on a windmill it might not last very long before something goes wrong. Possibly gearbox before motor. keeping oil in gearboxes is a continuous problem. Because this runs slowly my pesimistic view might not be waranted. I will look forwrd to where this thread heads to. Best wishes Oscar Oscar4u - for all your rotary cowshed repairs |
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| Air Bender Senior Member Joined: 25/01/2011 Location: AustraliaPosts: 206 |
Hi Caleb, I think gearing will be your bigest obstical. I have been working with 24V dc motor which is probably not the ideal motor to use but I had it lying around in the shed and replacments motors are cheap and easy to get. I have not run a rev counter on it, but I am esimating the it is spinning between 800 to 1000 rpm to get an output good enough to charge a 12V battery. Somthing Like a dc treadmill mptor seems to be what most people use. I have heard that you need to spin them at around 350 to 400 rpm to get any decent power out of them. You might be able to set up something like govertical is working on but with a bit bigger gearing on each set of pullys. All the best Dean |
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| Air Bender Senior Member Joined: 25/01/2011 Location: AustraliaPosts: 206 |
I had a look at the gear motor but what I saw in the specifications is that at 6rpm it makes more amps than what it does at 12rpm which dosnt seem quite right. If it puts out what what it says it looks like it would be an easy set up for your mill, but how long it will last only time would tell. If you do use this gear motor I would be interested to hear how it goes. All the best Dean |
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| Air Bender Senior Member Joined: 25/01/2011 Location: AustraliaPosts: 206 |
Back again, What you need to check with that gearmotor is that it is a permanant magnet motor, otherwise it may not work as an alternator. I had another look at the specs and the amps are how much power it uses to turn a certain load. I dont know if those specs are any thing to go by if you use it in reverse as an alternator. All the best Dean. |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Dean, if you change "makes more amps" to takes more amps it makes perfect sense to me. Remember, the nameplate on any motor gives its specs running as a *motor* and not as an alternator as is intended. I have doubts the gearbox stands up to being *driven* from its shaft for long if that is possible at all. For example, if there are two worm gears inside then its a one way gearbox only. The box would rob a lot of windmill power with such a high gear ratio. Klaus |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I would give gear motors a big miss. The problem is that the pinions are usually very small diameter. While that works fine driving a much larger gear, it will be hopelessly inefficient where the large gear tries to drive the very small diameter pinion. Cheers, Tony. |
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