Prototype anemometer / wind powered generator

6 generators page	magnet notes	hand cranked gen	AC to DC	more soon	back to 3D page
4-way cross 4 way.stl file 4 way.g file 4 way.scad file	main and coil 3D .stl file 3D .g file 3D .scad file	base 3D .stl file 3D .g file 3D .scad file	3-way cross 3D .stl file 3D .g file 3D .scad file	more soon	back to 3D page

These are some notes on a simple anemometer or 4-cup wind powered generator. This is not ment to be a state-of-the-art device; I have made it so that it easy to understand, so you can clearly see what's going on and, if required, easily modify it to your requrements. The local "99p" store had a pack of four of the metal cups which I thought would be an inexpensive starting point for the project. I built a prototype using magnets, coils of wire, wood and perspex and used a band saw and a router. It made about 5V in a good breeze (it requires a rectifier circuit but more on that later). Thinking that many people don't have skills using (or access to) power tools etc. I thought it would form a great 3D printer project. Science students at a school who have an art or design department with a 3D printer can now create a working device ... they can then focus more on the science involved (Faraday induction etc.) rather than spending time developing the practical skills required to make one by hand. I hope it will make an interesting science fair project for high school students who wanted to a make a device that could charge their phones, run an LED light etc.

4 cup cross

Some of the 3D printed parts: the 4-way cross peice, the main unit and the square coil former lip.
The later part clips on to the other piece to form a bobbin to wind the coil.

The four cups are fixed by 3mm nuts and bolts to a 3D printed cross piece that also has a central hole for a shaft (3mm threaded bar). The wind turns the cups which rotates the shaft. The shaft goes to a magnet enclosed by a coil of wire. The magnet is a rare earth one and is unusual that it has the magnetic poles at the sides rather than top and bottom. It is important that you get the right magnet as a standard one will not work. When the magnet rotates, the change in magnetic flux created in the coil, generates a current / voltage (by Faraday induction). Note: there will be no change in flux through the coil when a standard magnet rotates so no current will flow in the coil, see 'magnet notes' link. This is an alternating current (AC) generator and so it needs a rectifier and capacitor circuit to smooth into DC (see AC / DC link). The theory has been covered in the links (above) so I wont go into more details here.

The 3D printer has a distinct advantages over making the device by hand. For example the shaft channel that takes the 3mm threaded bar on the main 3D printed device is not an easy thing to drill accurately parallel but the 3D printer of course simply lays down the plastic creating a perfect channel. With a 3D printer you can print out as many versions as you need to, to get a really perfect fit for the particular magnet you intend to use. This is easier for a beginner to do using software (which can be adjusted to an acuracy of ca. 0.1mm) rather than trying to make everything new by hand.

Three photos, left: The 4-cup gen, middle: close-up of the magnet housing and right: photo of a 3-cup support version of the cross piece.
You can just see a hex nut in a 3D printed counter sunk hole. There is also an extra nut on the shaft that can be tightend up onto the counter sunk nut to get a tight fit.

modifications / hints and tips
The cross piece that holds the cups will rotate when the wind interacts with the cups. The cup orientation will determine the direction of rotation (irrespective of the wind direction). It does not matter which way the generator turns but the wrong rotation direction will tend to unscrew the nuts holding the shaft! So you need to make sure the cups are the correct way around (you can work it out by trail and error and the photos will help). I put a bit of thread-lock glue on the nuts at the cross piece.

The magnet sits very neatly into its square hole. You have to fit it in place and then carefully screwing in the thread from above while holding the top nut in place above the magnet. As the thread goes in it will eventually emerge from the bottom of the magnet and you can then add the final nut (its a bit tricky). I applied thread-lock glue to the nuts and also into the shaft going through the magnet.

Once the magnet is in place you can pop on the square coil former via the four 3D printed pins that locate into the 'chimney' on the other piece. A dab of super glue on the pins will help. Then wind on the wire in the bobbin that has been created. I used 500 turns of 35 SWG wire in the prototype. The internal resistance of finner wire will we greater and so you will get greater power loss. However if you just want to use the device to show the principles of wind power to simply light an LED for example, a 1000 turn coil (easier with finer wire) will light the LED with less wind speed.

Once the magent is in place and coils wound, you can fit the 4-way (or 3-way, see below) cross piece on the shaft and see if it all turns ok. You might have to adjust the nuts around the magnet and the nut that holds the shaft at the top of the main 3D printed unit. A little light oil in the shaft channel will make it rotate easily. You can simply wire in an LED to the two coil wires or wire up a rectifier and capacitor to create a DC output (see links in table).

In the bottom couple of photos you can see a 3D stand I made so that it can sit on a table - you can use it as a demonstration model etc.

I noticed that the 99p shop near me stopped selling the cups for a while. They have now brought them back but in packs of three not four ... they also seem thinner. I guess I am the only person who is actually happy about this, as the lighter they are better! So I have built a 3-cup version. The 4 cup may have more power / torq. than a 3-cup but the later will probably spin faster. The simple coil-magnet generator is a 'velocity' device - in other words the faster the rotation the greater the voltage - so the faster speed is better. I also built-in a counter sunk hexagonal hole into the 3-way cross piece. This makes it much easier to get a tight fit to the shaft.

You can see in the last photo (bottom of the page) that the coil lies to one side of the center of the magnet. In principle you can add another coil set to the free side to double the power (wire the coils in series but be carefull about the phase / wiring otherwise the voltages will cancel instead of add). Note: it may be much more difficult to directly 3D print a double coil and you might simply make another piece that can be fitted on.

In this very simple design the cups are connected directly to the magnet. As the generator creates a voltage proportional to the speed the magnet rotates it would be a good modification to use a pully system drive from the shaft to the magnet to speed it up. This would of course make the design more complex and less robust but it would mean that you could in principle create more voltage at lower wind speeds (provided the gearing does not stall the movement of course).

I plan to record the AC voltage created by the generator for different wind speeds (against a calibrated wind speed meter) so that we can make this simple wind powered generator into a working anemometer. Watch this page ....

The 4-cup device on its base

A 3-cup version of the device. This should spin faster than the 4-cup and so should generate more voltage in the coil of wire (see text above).

THE CREATIVE SCIENCE CENTRE

Dr Jonathan Hare University of Sussex, Brighton.
e-mail: j.p.hare@sussex.ac.uk

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