This is a derivation of the OpenSCAD project submitted by Matt Larson. This was a project done by a high school physics class investigating the factors that affect the power generated by a wind turbine. This was the first full class 3D printing project that I did.
I've made a couple very minor changes to the OpenSCAD file to make the variable names more intuitive to my students. I also added in some clarifying comments where I thought they would help and cleaned up some Depreciated code.
You may need to add a raft for some designs to keep them from falling over. If your machine can do a brim this would also help.
We used 2 perimeters on our turbine blades.
Clean off the flat rectangle. We used a steady hand and razor blades. We found you had to shave the bottom corners of the base off to fit easily into the hubs. Be very careful as the turbine blades break easily. You could print with more perimeters to increase strength, but then you risk them being too heavy to get turning.
This was made in OpenSCAD from a design originally submitted by Matt Larson.
Each of my two physics classes picked two parameters to vary. We ended up with:
- Angle – Which was really twist
- “Fat Point” – Ratio of top length to bottom length
We created 5 different versions for each parameter. I let the students decide what they wanted to set the parameters to as long as the blade was not absurd.
Overview and Background
A few years ago I managed to find money to buy a Makerbot Replicator for my classroom. It really is like magic. We spent quite a bit of time 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). Then I discovered OpenSCAD. The beauty of OpenSCAD is that you can create or find a program that generates the 3D design. As with many programming languages variables are declared at the beginning of the program. These variables can be made easily identifiable. Students do not need any 3D design or programming skills. All they need to do is change the variables in order to change the underlying design. See my short video above for clarification.
- Students will build a mathematical model of the effect changing a wind turbine parameter has on its output.
- Students will analyze data and models created by other groups to make predictions.
- This project was done with high school physics students at the end of the school year.
- I believe this could also be done in a high school math class.
- If the "mathematical model" was removed and students were only expect to look at graphs made by each group I believe this could be done in Middle School or even upper Elementary.
- High School Physics
- High School Math
- Computer Science
- Upper Elementary or Middle School Science
- NGSS Scientific and Engineering Practices
- Developing and using models
- Analyzing and interpreting data
- Using mathematical and computational thinking
- NGSS Crosscutting Concepts
- Patterns - Analyzing data to determine rates of change. In this case, the constant rate of change in velocity and the varying rate of change in position.
- Scale, proportion, and quantity
- NGSS Core Ideas - Physical Sciences
- PS2.A: Forces and Motion
- PS3.A: Definitions of Energy
- PS3.B: Conservation of Energy and Energy Transfer
- PS3.C: Relationship Between Energy and Forces
Lesson Plan and Activity
- Introduce the project and show students OpenSCAD. Show them how to change the variables and render the model.
- Allow students to play so they can determine what each variable does.
- Have student groups each identify one factor to change, while holding others constant. Note, this might mean two variable must be changed. Changing the "bottom_height" without changing "top_height" would change the total blade length as well. Students might change the ratio of top and bottom heights but keep length constant.
- Student groups share what they want to change with the class for discussion and input.
- Students create 5 different states varying their factor of choice. See my picture above where the "fat point" (or ratio of top to bottom) is changed while all other factors were kept constant.
- Print. It took my printer 3-4 hours to print a full set of blades, That is 3 each or your 5 different designs.
- Clean and mount blades in the hubs.
- Student groups test their blades
8.1 Method One: Press fit the shaft of a small hobby motor into the hole on the hub. Attach the motor leads to a volt meter. Position 20 cm in front of a box fan set to high. Read voltage.
8.2 Method Two: Mount blade on a straightened a paperclip. Position 20 cm in front of a box fan set to high. Use a Vernier or Pasco photogate to measure the spin rate.
- Students create a graph for their data and fit an equation using the regression function on their calculators.
- Students share data, graphs, and mathematical models with the class.
- Student groups use all of the data to design the "optimal" wind turbine blade
- Print and test final blades
- Day one: Steps 1-5 above.
- Print over night
- Day two: Clean and mount blades (step 7). Takes longer than you think.
- Day three: Steps 8-9
- Day four: Steps 10-11
- Print over night:
- Day five: Test and crown the winner!
- Student Skills:
Know how to make an x-y scatter plot
Know how to use the regression function on their calculators
Know how to analyze graph data
- Stuff needed
Test Equipment (dc hobby motor+volt meter or photogate)
Some way to mount. I used a ring stand and attachments found in chemistry room
Rubric and Assessment
I looked only at the finished, optimized blade design. Some students ignored the data and created a design based upon what they thought would make a good design. As you might guess, these did very poorly. The groups that did the best used all of the data collected and changed each of the variables. This became a great teachable moment.