e-mail: bob@sc4geography.net


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Building a windmill can be dangerous. You might end up hurting yourself or someone else. Take all precautions. The following is a description of what I did. If you follow these descriptions, you might still get hurt. The following is merely a description. I am not attempting to direct or instruct anyone. There are no promises for success.

The biggest advantage to building your own windmill is the fact that you can do it for much less money than buying a manufactured model. However, if you tried to buy all of the parts for your windmill new off the shelf, then you will probably end up spending more than the price of a manufactured model. The good news is that many parts are available as salvage material. It takes some creativity and a willingness to perhaps run around town getting the parts that you need in order to build your windmill.

Another advantage to building your own windmill is that it can be incredibly fun to do. Whether the cost of your windmill is high or low, you should enjoy the ride no matter what. Of course, try not to kill anyone with your windmill in the process (or your marriage). The process can also be very educational for you or anyone else who might be watching (kids can become especially interested in a project like this).

I started the process by purchasing an unused treadmill motor on eBay. The motor was never used but was about 6 or 7 years old. Any DC motor can be used as a generator if spun backwards. It produces direct current (DC). The motor is rated as 260 volts at 5 amps (5100 RPM). The output of electrity is rated at 180 volts (5100 RPM). With my windmill, I can get approximately 500 RPM in a 20 mph wind using a gear ratio of 8 to 1. This produces approximately 40 volts DC.

The DC motor that I purchased has brushes and therefore will probably not last as long as a brushless model. Also, my DC motor is not weatherproof. I paid $39 for this DC motor because I was interested in getting the windmill completed in a timely manner. If you take the time to look a little harder, you can find brushless motors that are more weatherproof. You might try tearing into salvaged items such as washing machines, sewing machines, battery powered tools, treadmills, etc.

The next step involves designing the windmill blades. This process can be very educational and you can get carried away with this if you are not careful. If you are looking for the perfect design, stop right now. After 3000 years of windmill technology, there is still no perfect design. There are advantages and disadvantages to every design (in my opinion). If someone talks poorly about your design, take it with a grain of salt. Afterall, you are harnessing the energy of the wind and converting it to electricity. So what if you are losing 10% or 20% of your potential, it's all free. And you might have to spend an extra $100 or $200 to get that extra 10% to 20%. You need to come to these decisions on your own. Cutting energy losses AND cutting expenses are both very important goals and it can be frustrating trying to decide exactly how to do it.

If you want to test different blade designs, try to do so with material that is inexpensive or disposable. For instance, I used 4-inch and 8-inch PVC plastic pipe and also 8-inch cardboard tubing (for cylindrical cement foundations). After all of this, I ended up using flat blades in stead of curved (two-foot radius). All of my testing was educational for me and I am confident about my decision to use flat blades (balancing costs, efficiency and time). You might come up with a different result.

A three terms that you will become familiar with in studying blade design are "start-up wind speed", "swept area" and "solidity".

Start-up wind speed is a crucial number. It refers to the lowest wind speed that will start your windmill in motion. When an object is at rest, it likes to stay at rest. Therefore, it can be difficult to get the windmill going. You want to reduce the start-up speed as much as possible. However, doing so will cause you to sacrifice energy production at higher wind speeds. Blade design has a lot to do with it. So here again, there is no absoultely correct way to do it. It is an art form. There is lots of literature out there regarding start-up wind speed for windmills.

The swept area simply refers to the diameter of your windmill. The larger the diameter, the larger the swept area. The larger the swept area, the more energy you can theoretically capture from the wind. However, you need to remember two important facts. First, extending the length of your blades also adds weight to the windmill and therefore increases the amount of energy needed to make it turn. A figure skater spins faster with arms pulled in and slower with arms straight out. Secondly, extending the length of your blades also requires better engineering to make sure that you blades don't go flying off in a high wind. If you are building a windmill that is less than four feet in diameter, you don't need to have much technical skill to get the job done. If you are building anything larger than this, you should have a professional take a look at it. Remember that these windmills can hurt people if they start to fly apart. You don't want to be responsible for anything like that. Play it smart.

Solidity simply refers to the amount of swept area that is filled with the actual blades. The old style farm windmill has high solidity (approaching 1.0) because the swept area is filled almost entirely with blades. These windmills are used for pumping water and therefore need high torque. The large commercial windmills that generate electricity have only three narrow blades. These windmills have a low solidity value (approaching zero). Lower solidity usually equates to higher RPM, but you can easily do some of the testing yourself on your own machine. Remember, it is important that you feel good about your design. When you look out in your backyard and see your windmill spinning, it should be a good feeling.

Of course attaching the blades to your generator (DC motor) can be a trick in itself. The testing you do with your blades will probably be accompanied by the testing of various hub designs. Getting the hub attached to the generator spindle can be difficult. You might have to go to a metal shop or a tool & die shop to have a part made. Or you can use plywood or even masonite to test various designs. If you go to your local hardware store or supply store, you can purchase paneling or pastic bathroom lining in 4'x8' sheets at a relatively low price. You can use these materials at many different stages in the windmill building process. Have them cut it into four smaller pieces if you can't get it into your car. It is also easier to work with these smaller pieces in your shop or garage.

I ended up using an old bicycle wheel to mount the blades. The bicycle wheel also provides me with a pulley system that allows me to gear up the generator. I was leary of the idea at first because I thought I had to mount both sides of the bicycle wheel axle to some sort of frame which would restrict the size of my windmill blades. I wasn't sure that bolting only one side of the bicycle wheel would provide enough support for my blades. In the end, I found that bolting only one side of the bicycle wheel was enough as long as it is a rear bicycle wheel with coaster brakes. The reason it needs to have coaster brakes (brakes inside the wheel hub) is that there is a steel brake arm that provides critical support for the bicycle wheel. This brake arm creates a triangle of support between the bicycle wheel and the windmill post. I also took the bicycle wheel to the local bike shop and had them remove the brakes from inside the hub (less friction). They had the parts to replace the brakes. It was worth the effort-- the wheel spins fast and long.

I wasn't the first to think of using a bicycle wheel as a windmill pulley. Ted Baer also has a design that utilizes a bicycle wheel and he came up with the idea before me. Click Here to see Ted's project. His blades are mounted in a different manner (read on).

The windmill blades can be attached to the gear on the bicycle wheel itself. Afterall, the gear drives the wheel when you ride your bike-- simply replace your leg power with wind power. You might need to design something out of plywood or masonite to get this done. Try bolting the plywood or masonite to the teeth of the gear. You will need to drill tiny holes in the plywood in precisely the right spots and you will need about 3 or 4 hands and some extra tiny fingers to get it bolted. It can be frustrating-- hang in there. Then mount the blades to the plywood or masonite. Make sure that your windmill blades are oriented so that your bicycle wheel turns forward (clockwise as the gear is facing you). If it turns counter-clockwise, the wheel may not turn properly with the windmill blades.

Then you can mount your generator to the post just below your bicycle wheel. Remember that your generator also needs to pivot in the wind along with your windmill blade assembly (more below). You will need to get a fan belt to connect the bicycle wheel to the generator. Try to reduce the amont of friction by utilizing a thin belt. You might even try nylon string to start out. You can experiment wth different belts after the windmill is finished.

Once you have the generator and the hub and the blades ready to go, you should decide how to mount your windmill. Do you want a lawn decoration that is only three feet off the ground or do you want an 80-foot tower (or something in between)? The higher the windmill, the more wind it will catch.

Once you decide on the height of the windmill, you will need to come up with a design that allows the windmill to pivot in the wind. Initially, I used a piano castor swivel mounted on top of a 3x4 post (remove the wheel, invert onto the top of the post and utilize the swivel plate for your windmill). You can buy a swivel castor new for about $15, but you can easily salvage one too. Be creative! There are lots of swiveling items out there that can work. It doesn't have to spin as fast as a top. It just needs to be able to turn in the wind.

Now you need to double-check that your windmill is safe. Is it so close to the ground that someone might hit their head on the blades? Is the tower so tall that it might topple over in a high wind. Again, if you are building anything over 6 feet, get a professional to check it out for you. Most local ordinances require that a windmill tower needs to be able to fall on your property. In other words, if you have an 80-foot tower, then it needs to be at least 80 feet from your property line.

Do your neighbors like your windmill? Even a small lawn windmill can anger your neighbors. Talk with them. Love thy neighbor.

If you have any questions at all, please feel free to e-mail Bob Hunckler at the following address: bob@sc4geography.net

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