# Fun with a 3D Printer – Physics Wind Turbine Project

Almost a year ago I managed to find money to buy a Makerbot Replicator for my classroom. It really is like magic. Most of the year we’ve really just been playing. Printing out cool stuff from the Thingiverse and a few project enclosures for electronics projects.

I’d been wanting to do a cool design project with my physics students, but never really knew what it should be. 3D design is not a skill in the wheelhouse of virtually any of my students (our CAD program died a few years ago). It turns out there is a cool program that lets you create 3D designs programmatically. It’s called OpenSCAD. The beauty of this is that you can create or find a program that generates the 3D design. Then all you need to do is change some of the variables to get a new design.
I decided to give this a try in my physics classroom. We’re in the time of year after the seniors are gone and now the juniors feel like they should be gone as well. I found a cool Mini-Wind Turbine model on the Thingiverse that was created in OpenSCAD. I played with it a bit to figure out exactly what the variables did and then introduced it to the class. Next year I’ll let them figure out what each of the variables does for themselves.
Each of my two physics classes picked two parameters to vary. We ended up with:
• Length
• Width
• Angle – Which was really twist
• “Fat Point” – Ratio of top length to bottom length
We created 5 different versions varying our on parameter. I let the students decide what they wanted to set the parameters to as long as the blade was not absurd.
Actually we did end up with an absurd blade when it came to twist, but the group that wanted it were convinced it would be the best. So I went ahead with it.
I asked students to graph and find the relationship for each of our four parameters. Unfortunately none of the parameters gave us very good mathematical relationships. I think we might have needed bigger variation in some and more data points in between in another. Next year I may have students fill in some of the gaps.
Once data were analyzed I asked them to design the perfect wind turbine. Some groups relied on their data and some did not. It should really come as no surprise that the groups that relied on the data did the best. Of these most just picked the one best data point in each and put them together. The very best one extrapolated from their data to predict a better solution. It’s nice when things work out the way the should like that.
The best part for me was how surprising our results were. We all had the image of the big majestic wind turbines in our heads. This, however, was not the shape that we found to be the best. The one we found to be the best looked the least like our pre-conceived notion. It had fat stubby wings rather than long and thin.
Some nuts and bolts details:
• 3D Pinter costs \$2000ish
• Plastic is fairly cheap. If I had to estimate, I used between \$10 and \$20 worth of plastic on this project.
• One full set of 15 blades (3 each of five different states) takes between 3 and 4 hours to print. One set all by itself  40 min to an hour. Time varied depending on the design.

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