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.
A small flashlight bulb was actually easier to get to glow than lighting a LED, when driving a 6 to 1 gear on a “solar grade” motor by hand. But it required too much torque for a small and simple wind turbine.
A LED worked with a turbine and a single step 6 to 1 gearing, but only at really high wind speeds, needed to get a high enough voltage. But I wanted the kids see it functioning, without having to wait for a strong wind. To apply a higher gear ratio in one step needed a larger gear wheel which I could not find at a low price. A two step gearing gives to much friction with the cheap and simple construction techniques suitable for a kids workshop (remember we are talking about gearing up, which is more critical to build quality).
But 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.
Apart from attaching leads to the motor/generator in advance (“solar” motors are often sold with leads anyway) the circuit is built up without soldering, as I prefer to avoid that when working with 20 kids aged 6 to 12.
All that was left was making some “templates” for the steps that need accuracy and gathering the materials and I was ready for the workshop. Check the result in the video below and read how we built the wind turbines in this Instructable.
My special thanks goes to Emma, for her assistance when taking extra pictures showing the detailed construction steps.
Thanks for the votes for this entrie in the MakerBot Challenge!
Step 1: Materials and Tools
1 piece of 2mm thick balsa 10 cm by 40 cm or 4 pieces 10 cm by 10 cm
4 bamboo (meat) skewers 30 cm long, about 3mm diameter
some cellotape, at least 19mm wide
large gear (about 60 mm diameter, Opitec part 840088)
a piece of scrap wood, 3 cm thick and about 6 cm by 6cm in size.
some non-stick paper,
1 small stick of hotmelt glue (low temp type when working with kids)
a cabinet screw with an unthreaded part, fitting loosely the gear hole (4mm for the gear mentioned above), about 35 mm long. A brass screw will last longer in humid conditions, I found out screws with a nominal diameter equal to the gear hole, actually fit loosely.
4 washers fitting the screw
paint and varnish (optional)
For the generator:
a “solar grade” toy motor with 7cm leads (FF 130 “solar motor”, Opitec part 224176 works great, but needs leads to be soldered to the motor. The RF 300, Opitec 224154, comes with leads, but is less resistant to rain)
a small pinion gear of the same module as the large gear (Opitec 841187 with adapter 842022)
a (steel spring) clamp fitting the motor/generator (Opitec 225074)
a 25 mm long bolt and nut. I choose M3, allowing for all drilling to be done with a 3 mm bit.
For the Joule Thief:
a ferrite toroid (e.g. Conrad 507997 or 508039)
a 2N3904, BC 337 or equivalent transistor
a 1kOhm resistor
1 to 3 LEDs (the clear ones are easiest to see lighting up in sunlight)
2 times 20 cm of insulated thin gauge electrical wire (twisted strands from telephone or network cable are perfect)
5 small cabinet screws, preferably brass (more durable contact). I choose shortest 3 mm diameter ones I found, allowing for all drilling to be done with a 3 mm bit.
For the mast
a 27 cm piece of 20mm diameter PVC electrical tube
a 75 cm to 1 m long piece of 16 mm PVC electrical tube
2 tie-wraps (pretty small ones are OK)
a junior hacksaw
a flat working surface (theoretically 31 by 31 cm, but take double to work with some comfort)
a hotmelt gun (low temp type when working with kids)
a drill (preferably column-type) and a 3mm drill bit
screwdrivers fitting the screws and bolts used
some templates can be made out of scrap wood as explained in the following steps
Step 2: Making the Turbine Blades
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.
Step 3: Turbine Construction
Make sure all the blades are pointing the same direction (clockwise or counter clockwise) and touch the flat working surface with their tip. This is obviously very important to get a good angle. Now, pour hotmelt glue in the hole, taking care not to spill any on the gear's teeth (see how a piece of scrap cardboard can be used the help prevent that). Check if all blades are in the right position and let the glue set, before removing the screw.
You might want to reinforce the glued connection on the other side, but to my experience that is not needed unless the turbine is accidently dropped or something like that.
Step 4: Drilling
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.
Step 5: The Generator Joule Thief (1)
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).
Step 6: The Generator Joule Thief (2): Electrical Connections
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.
Step 7: Mounting the Turbine
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.
Step 8: Tail Vane
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.
Step 9: Installing
Step 10: Ideas for Further Developments
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.