Way of the Wind Turbine

Pass around a generator, with an LED on it, and let students practice turning it with their hands. 

Ask how they might turn the rotor without having to touch it, and guide the discussion through the notion of a turbine blade as a combination of two simple machines, the inclined plane and the lever. 

With paper sketches, give students space to consider what number of rotor blades they will have, whether they will stretch out to the maximum length possible, the maximum width, what shapes will guide their design.

• Practical limitations serve to constrain things a bit, so here are a few that might serve:
• Too few blades means that the weight of each blade works against the rotor’s ability to move. Too many blades means they each crowd each other potentially reducing effectiveness to the point of not rotating, despite angle. Recommend between 2 and 12, but if a student feels strongly, let their design be proof.
• Too thin of blades break easy, too thick of blades are heavy, and don’t encourage movement by airflow. Recommend between 1 and 3 mm.
• Too short of blades won’t catch much wind, too long will be impractical to print. Recommend blade lengths between 20 mm and 60 mm.
• Too narrow of blades are ineffective at catching wind, too wide will overlap and interfere with each other. Recommend between 10 and 30 mm
• Angle of incline is critical to functionality, but how much is best? 0° and 90° are demonstrative physical limits, but it might also help students to constrain away from angles that are “practically near” those limits, where the physical effectiveness is indistinguishable from the limit. To that end, recommend between 20° and 70° The demonstration group was constrained to 22.5°
• The shape itself is an important variable, and worth discussing to a point.
• The half sphere stretches to a rotor blade that looks very near the recognizable one in most production turbines.
• The demonstration group also used a triangular wedge, and box.
• Once students have considered and brainstormed a few possibilities, ask them to lock in their choices for shape, count, and other aspects which are open to variability for the learning group at hand.
• The demonstration group submitted their choices in a google form that gave them 3 variable parameters with 4 available selections in each.
• This ensured that every rotor was unique to a student who could feel sufficient agency with the selections they made. 

Phase 1: Hub and shaft-mounting hole. 

• Add a hole cylinder with a height of 12 mm, and a diameter of 3 mm (measure the shaft on the generator component to be sure, we will want a snug fit.)
• Add a solid cylinder with a height of 11 mm, and a diameter of 12 mm (or 4 times the shaft diameter)
• Add one more hole-cylinder with a height of .1 mm, and a diameter of 130 mm.
• Use the align tool to center all of these within each other. 
• They should all rest at the bottom. 
• Resist the urge to group them yet. 

Phase 2: Single blade shape and joining shaft. 

• Add a solid box, and make it 25 mm wide, 6 mm long and 3 mm in height. 
• Next, pick any solid shape, and make it 60 mm wide, 25 mm long, and 3 mm high. (the half sphere works nicely here, as a classic looking shape. Some shapes are inherently problematic, but that’s part of the discovery) 
• Hold the shift key and click the shape of the rotor blade, the box made before it, and the hole cylinder at the center of the hub. 
• Press the L key to activate the align tool, then click the hole cylinder at the center of the hub. 
• Click the alignment tool on the left, then center (front to back) and center (top to bottom). 
• Click an empty space or press escape. This will make sure nothing is selected. Then right-click and drag to orient toward the right side view. 
• Click the rotor blade and use the rotate handle to incline it counterclockwise. (22.5° is the first automatic stop along that path, and is a fine amount to go with, but it needn’t be SO specific.) 

Phase 3: Duplicate and Repeat. 

• Consider how many blades, then divide 360 by that number. Write that down. 
• Select the blade and its box, as well as the large hole disc underneath everything. 
• Hold the “Ctrl” key and press the letter “D” to activate the Duplicate and Repeat tool. Nothing may appear to happen. 
• Click the top of the view cube to view from above, then click the rotate handle which appears normal to the view, and then click the number that appears by it. Change that number to the one written down, and press “enter” to confirm. If this works, the original rotor blade should appear to stay where it was, but a new one should appear rotated about the hub by the number of degrees entered. 
• Hold the “Ctrl” key and press “D” until the chosen number of rotor blades have appeared. Any mistake in this can of course be undone with “Ctrl” + Z

Finalize and Export!

• Click and drag to select the disc, which has also multiplied in this process. Delete all copies of it, so only the completed turbine rotor is left. 
• Select all of its parts, and use “Ctrl”+ G to Union Group them. 
• Click “Export” from the row of buttons at the top right of the workspace,  
• Find the “.STL” button in the menu that pops up, in the “For 3D Print” section. 
• Save the resultant downloaded file for the next step. 

Import the model into the slicing program, and check for things like dimensional consistency.

• We used millimeters for our design dimensions this time to ensure that we exported that way, for this machine.
• It is also possible to design in other units, then convert as needed.

Supports may be needed, depending on the angle of pitch given the rotors.

• If supports are not desired, consider the ways changing the design might render them un-needed, and revel in the power of being the designer.

Configure settings for the machine, and slice.

• These can be dependent on a variety of factors dependent on the machine, configured nozzles, and available filament.
• For best results, prototype with the included example rotor then greet the students with the confidence of proven settings. 

Preview the sliced rendering to ensure that all desired settings have been considered.

• In our case, the program offered a “raft” inclusion to join the supports, so the preview helped to see what that would entail.
• It is also a good way to understand how long each print will take.

Name each file (perhaps according to student, or design variation?), and export to print file.

• Students are unlikely to be able to export directly to the machine even if it supports that, as only one file can be printed at a time.
• Consider having multiple media storage options like flash drives and SD cards, to which student files can be exported.
• It is also possible to have students export to network storage, or send the exported files via email.

Batch and print student files.

• Best practice may include a job-tracking sheet that maps each submitted file to a student, and allows for tracking which ones have been printed, especially considering it may take some time to get them all, and may require coordinating with colleagues to make best use of available printers.
• An example of one is included, which we also used to track each student’s chosen variations.

The Tower:

• Two parts include a long narrow slit, allowing them to be assembled at right angle, with each part fitting into the slit of the other.
• They can then be joined with the rectangular part, interlocking the tabs with complementary slots.
• These parts should not NEED glue, but a little around the base tabs would certainly help keep the assembly firm.

The Generator:

• The generator is then attached using four 3mm machine screws and nuts.
• This part has two installation options that would seem to fit, but one allows the base to continue to support it in “high wind situations” where the other would simply topple over.
• It is an intriguing classroom discussion to let the students make the decision as to which configuration is which.

The Rotor:

•  The rotor should slide onto the shaft, snugly enough that it does not fall off.
• If it is too loose a little tape on the shaft should help.
• If it is too snug, or doesn’t fit, it can be drilled to match the size of the shaft.

LED for Demonstrations:

• For demonstrations the LED can be inserted into two adjacent slots on the connector from the generator.
• LED’s are directional, so it is important that the cathode (short leg) goes into the center slot, with the longer leg going into either of the outer ones.
• There is a hole at the top of the tower for mounting a 5mm LED, and a little adhesive can help it stay in place there.  
• It’s also worth noting that if alligator clips are part of testing leads, they can be clipped to the legs of the LED without removing it.

Attach the test leads to the output, and move the wind turbine into the path of the blower.

Let the number stabilize, and write it down.

After everyone’s designs have been measured, a discussion can be had about what features allowed for the highest values in voltage, amperage, or the wattage that results from multiplying the measured voltage and amperage.

Afterward, the following questions can be used as a summative assessment, or even just exit ticket discussion:

• Outline the steps of the engineering design process. 
• Why is it important to consider shape, size, and material when designing wind turbine blades?
• Describe the features that are important in creating wind turbine blades.
• Why is it important for wind turbine blades to be aerodynamic?
• What factors could affect the efficiency of wind turbine blades in capturing wind energy?
• Identify the components of a wind turbine.
• Explain how wind energy is converted into electrical energy in a wind turbine.
• Describe the role of wind speed in the efficiency of a wind turbine.
• What is the purpose of the rotor in a wind turbine?
• Explain the role of wind turbine blades in harnessing wind energy.
• Why is testing an essential step in the engineering design process?
• Describe the testing environment used to evaluate the wind turbines.
• How does harnessing wind energy through wind turbines contribute to sustainability?
• Discuss one environmental benefit of using wind energy.