Masynmachien says, "For my latest workshop in my daughter’s school, I wanted to let the children each make a wind turbine. It wanted it to be functional, powering a small light, and it needed to be cheaper than 6 Euro a piece, which ruled out any commercial kits. The workshop was for 20 kids, which ruled out scavenging hard discs motors or stepper motors and such. Low cost 'toy' motors, on the other hand, need really high rpm to light up a small bulb or a led. Fortunately, the type of motors used in solar cell driven toys and kits work better. And these are still available for under 2 Euro. An LED worked with a turbine and a single step 6 to 1 gearing, but only at really high wind speeds. But I wanted the kids to see it functioning, without having to wait for a strong wind. Our good friend the Joule Thief came to the rescue. With this little circuit added, the LED lights up at a breeze. Moving the wind turbine by hand easily lights up the LED. I estimate it starts at wind speeds below 10km/h. And everything still holds up at strong winds." Since originally posting this project, masynmachien notes that he has also built these turbines with these geared motors instead of a Joule Thief.
Materials and Tools
The turbine blades are made by sawing three of the balsa squares as shown. Keeping the turbine very light makes it very forgiving for inaccuracy’s and unbalance, but to help make the blades all the same size, I did make sawing templates. Three of the skewers are cut in half (it is a good idea to cut of a couple of mm of the sharp point, to limit the risk of anyone hurting herself or himself). Take care of the grain of the wood. It should be close to perpendicular to the cut, or the blades will break easily. The forth square and skewer are kept aside for the tail vane. With some cellotape the skewers are provisionally attached to the blades as shown. The assembly is laid down on some anti-stick paper and some superglue is run in the joint, (something I do myself for the younger kids). When the glue has set the rest of the tape is bent over and attached. Now is a good time to decorate the blades.
The 27 cm piece of 20mm diameter PVC tube is prepared to be the central “support” onto which all other parts are attached. This means first some drilling has to be done. All holes are 3 mm Only one hole needs to be in an accurate position from one other, the others holes are not critical. First the hole for the motor/generator mount is drilled about 5 cm from and goes completely through. The motor/generator mount is attached with a bolt and nut. There's a little trick to that: first the mount is attached hand tight, with the curve of the metal following the curve of the tube. When it is twisted to its final position the spring metal provides tension, locking the assembly into place. Now comes the critical hole. It needs to be drilled perpendicular to the first one, and at a distance along the tube determined by the gears and motor/generator used (18 mm with the Opitec parts mentioned above). The motor/generator mount can be bent a little to adjust for small errors, but taking care with this drilling will avoid this. Therefore a template fitting the tube and motor/generator mount was made as shown. This hole goes completely through also. Now five holes are drilled near the top of the tube, roughly in the pattern shown. These holes need only to go through the tube wall once (don't worry if they go through completely). I adapted the template to help positioning these holes, but that was an overshoot.
The generator Joule Thief 1
The basics of making a Joule Thief are described in a number of Ibles, so I won’t go into detail, but stick to explaining the solderless construction used here. It is helpful to check out the circuit at Evil Mad Scientist to have some idea of what connections you are making. Obviously the motor/generator replaces the battery. Prepare the double wound toroid by coiling the pair of twisted wires. Four to five windings should do it. Loosen the wire ends and put two opposite ends back together (twist them together for now). Put the pinion gear onto the motor/generator and put it in the clamp as show (pinion facing the other side than the five holes pattern).
The generator Joule Thief 2
The electrical connections are made by inserting the right wire ends in the pattern of five holes and fixing them with the small brass screws. Not only is this an alternative for soldering, we also do not need to strip the wire. The thread of the screws cuts right through it, making the connection. If you are not sure which one is the positive one, just go ahead and check for what rotating direction the LED lights up after finishing all connections. Switch the motor leads after step 7 if it happens to be the wrong direction. At the workshop it showed the first insertion of the screw was difficult when connecting more than two wires. This is easy to solve by enlarging the hole slightly with a bradawl. To test it after assembly, turn the pinion gear quickly as shown in the video in the introduction. You might need to check both directions of rotation to find one working.
Mounting the turbine
Put in the axle screw in the turbine gear from the side of the blades. With 4 washers in between screw it in the tube, taking care the gear aligns with the pinion on the motor/generator. Again, slightly enlarging the hole with bradawl might help. When the screw reaches the second hole, on the other side of the tube, take care to guide it nicely through the hole, or the gear will not be angled correctly. Check if it runs smoothly and adjust. The gears should have a fairly loose grip on each other. Check if the LEDs light up by moving the assembly through the air by hand (as shown in the video in the introduction). Again, check the other direction if the first one does not work. The correct direction of rotation is the one with the turbine facing downwind from the tube. If it only works the other way around, switch the motor/generator leads.
Glue one end of the 30 cm skewer to the last 10 by 10 cm balsa square, taking care of the direction of the grain of the wood. The skewer should be glued across the grain of the wood, protecting the balsa from snapping along the grain. Attach the other end of the skewer to the bottom of the tube with two tie-wraps in cross. Align the tail vane in such a way that it keeps the turbine facing down wind.
Installing and ideas for improvements
Put a marble on the top of this tube and slide on the turbine assembly. The axle screw inside the tube, resting on the marble provides a bearing for the turbine to turn smoothly into the wind. Obviously the wind turbine should be positioned vertically for that. This basic junior wind turbine works well, but can use some improvements. One idea is to in weather proof all electrical connections with something like Plasti Dip. Do not worry about the motor/generator to much. Most toy motors resist rain quite well. To make sure you can put some grease to the axle and all openings. Varnishing the blades or replacing them with plastic sheet and possibly also the skewers will make it more durable. Although the bamboo skewers and balsa keep quite well. A furling tail vane could turn the turbine out of too strong winds. A classic furling vane mechanism with counterweight should not be too difficult to make. A bearing that keeps the turbine attached to the long tube could be helpful in strong winds. A longer 20mm diameter tube would help already. Another idea is to put the marble on a large screw inserted in a plug into the top of the 16 mm diameter tube. Then a small screw is inserted through the wall of the outer tube, locking just under the head of the large screw. An alternative attachment/bearing with a phone untangler could allow for the generated power to be transferred to an application separated from the rotating turbine. Another idea is to store the energy in a rechargeable battery, to power the LED(s) at windless evenings.