Your Alternative Energy Resource
LENZ II - Vertical Axis Wind Turbine:
Before we began building our vertical axis wind turbine, we set forth a list of rules and regulations to keep the project manageable and on schedule. The main criterion was to construct a VAWT that was kept reasonably simple so that the average farmer or homeowner could easily follow our lead. We also wanted to use parts that can be found at a local hardware store to give hope to others that they too have access to these items to construct such a device. One of the most important aspects in all projects is the cost and we felt this needed to be kept at a minimum so that the average person can afford all of the pieces that make up the entire windmill.
PROBLEM STATEMENT:
COIL WINDING DEVICE & STATOR:
There are two main components of this VAWT that are required to generate power. The first is the stator; which will be covered in this section and the next component is the rotor and magnet assembly, which will be discussed in the following section. The first piece that was built for this project was a coil winding device made from ¼'' plywood, which can be seen in figure 1 below. In order to get the same ½'' height of each coil a brass ½'' spacer was cut and placed over the bolts and the 14 gage copper wire was turned over the spacer. Specifically it had to be able to repeatedly produce triangular coils which were around 2" tall and 1.5" wide at the base. The coil winder was used to make a total of nine coils to fill the stator.
Figure 1: Coil Winding Device
After the coils were wound, they were placed in a stator mold made from ½'' plywood, as seen in figure 2. Due to the triangular shape of the coils the mold was made to be a perfect circle. This would also reduce any excess rotational weight. The coils were set into the mold and then taped into a perfect circle so that any slack would be removed. The coils were then labeled, " I, II, III, I, II, III, I, II, III". This would make for three loops of three coils, thus improving efficiency. The coils were soldered in place using a 3 phase wiring pattern and terminal buttons were attached to each of the loops, as seen in figure 3.
Figure 2: Coils Placed In Mold
Figure 3: Coil Terminal Buttons
Once cleaned and prepared, the mold was filled with a two-part epoxy resin sandwiched in between fiberglass cloth for improved strength. Blue pigment was added to the epoxy mixture for looks alone. The resin was added until level with the center of the mold. Then the top plate was bolted down tightly with 8 bolts positioned every 45 degrees and one in the center to ensure an equal distribution of the epoxy resin. The mold was allowed to cure for over 48 hours. Upon removing the stator from the mold no defects were found and the dimensions were near perfect, as seen in figure 4.
Figure 4: Final Stator
ROTORS & MAGNETS:
The other half of the VAWT's power generation ability lies in the rotors and magnets. The rotors used were cut from 1/8" steel plate and had a 9" diameter. The rotors were marked every 30 degrees until 360 degrees; this was done so that the magnets could be perfectly positioned around the rotor and ensure optimum efficiency. The magnets were attached to the rotor using a two part epoxy. Twelve magnets were placed on each rotor, in a north south, north south pattern. This layout can be seen in figure 5.
Figure 5: Rotor With Magnets
Figure 6: Rotor-Stator Assembly
The magnets chosen were arc shaped providing an increased magnetic surface area and made of Neodymium. They are considered rare-earth magnets and are the strongest non-electromagnets available. Once mounted to the rotor the magnets create a very powerful magnetic field. So strong in fact, that if a lighter steel would have been used for the rotors the magnets would have bent the two rotors together. An aluminum spacer is attached to the bottom rotor, as seen in figure 5 above. The stator is then laid on top of the bottom rotor and then the top rotor is placed with the magnets facing the ones on the bottom rotor (seen in figure 6). Caution must be taken in this step because of the large magnetic attraction. Wood blocks were used to gradually lower the top rotor onto the spacer.
Once the previous step is completed, this homemade alternator is nearly ready. The last few steps are to secure the stator perfectly between the two rotors without any contact and to fix the stator from rotating. A tri-star was mounted to the rotor which holds the spokes linked to the airfoils. Then the stator and rotors were then attached to a 1'' outer diameter steel shaft which acts as the center of rotation for the entire windmill . Now the VAWT is ready to generate electricity.
AIRFOIL SHAPE & DESIGN:
The airfoil ribs were taken into consideration and researched based on our problem statement. The overall goal was to find a shape or contour that allowed the windmill to self-start at fairly low wind speeds as well as easy to fabricate. Simply what this means, is unlike the Darrieus Rotor which needs a small push to begin the spinning action, our design will be able to start on its own, thus begin producing electricity in a wider range of wind speeds. The airfoil shape was dawn in AutoCAD (shown in figure 7 below) to provide a conceptual model and printed to scale for a perfect cutting template allowing for minimal error.
Figure 7: AutoCAD Airfoil Rib
As seen from the model above, we chose a baseline rib that has no camber, but allows the user to vary the angle of attack of the entire airfoil using the drilled center hole. The rib was made from ¾'' 11-layered plywood which contains three slots which are used for the 4' horizontal wooden spruce stabilizer bars. The figure 8 below is one of the actual airfoil ribs used in the construction of our project.
Figure 8: Wooden Airfoil Rib
Once all nine of the airfoil ribs and stabilizer bars were cut, the skeleton of the airfoil could be formed (shown in figure 9 below). Mounting blocks were used and positioned so that each of the three airfoils could be lined up the same way. The horizontal bars were then screwed and glued in place and the airfoil was ready to be wrapped. The wrapping material we chose was thin aluminum sheeting providing light weight, easy to bend, and great strength. The aluminum was bent at a 90 degree angle and slipped into the crack between the airfoil rib and stabilizer bar for improved support. From there, the sheeting was rolled to form the contour of the leading edge and was mounded to the wood using wood screws positioned every few inches. The process of wrapping the airfoil can be seen in figure 10 below.
Figure 9: Airfoil Skeleton
Figure 10: Wrapping The Airfoil
This process was done two more times for a total of three airfoils. Each airfoil end cap rib was then slotted to allow for a variable angle of attack between 0 and 20 degrees. This was done by drilling a half-moon arc and positioning two bolts, nuts, and lock washers in each rib to secure the airfoil in place at a given angle. The airfoils were then ready to be mounted to the spokes and the true size of the windmill can be seen in figure 11.
Figure 11: Tri-Airfoil Layout
BENEFITS OF WINDMILL PROJECT:
There are many benefits of this project, for it provides a cost-effective way to build windmills and produce energy from the wind. The components are easily produced and maintained allowing for the "average" person to set up and generate their own electricity. Components are available commercially from automotive, marine, and/or hardware stores meaning that any repairs will be cheaper and simpler. Using today's technology such rotors could provide a better efficiency as before and using commercially available wind turbines provides various pros and cons to real world application. One of the greatest benefits of this windmill project is to reduce our need for fossil fuels, thus cleaning up our environment to provide a healthy and smart future for the next generations.
Figure 12: LENZ II Windmill Prototype
