Introduction: Demo Wave Model Kit
Here are instructions on how to build a maker kit and your own private wave model. The project was designed to keep the costs of material and preparations down and be simple enough for anyone that can tie a knot and use a glue gun to build.
Step 1: Getting Started
I was challenged to come up with a project that would showcase multiple maker technologies at Maker Faire and would be accessible to kids of all ages. I originally was going to go with the mini-Wave Model by The Oakland Toy Lab, but as an engineer, even an electrical engineer, the uses of a thread joint where the force is perpendicular to the direction of the screw didn't sit well with me.
We decided to modify the design to make something that utilized laser cutting and required minimal manual steps to create. The first designed included a number of bolted joints, lots of acrylic and took over 10 minutes per model to cut on the laser cutter. We eventually settled on a design that provided a simple way to tighten the string and leveraged 3D printed bases.
What follows are the instructions on building this Hands On Demo Wave Model. You can make one or dozens for an event.
Here are the tools you'll need:
- Laser Cutter
- 3D Printer
- Hot Glue Gun
Here are the parts needed to build 1 wave model:
Step 2: Laser Cut Acrylic Spine
The base of this wave model is a simple laser cut acrylic spine. We used 1/4" acrylic cut on a laser cutter featuring notches that enable tightening of the string once tied.
A single model is about 3.25" x 12" or you can laser cut a dozen out of a 12"x24" sheet of acrylic using the provided DXF file where the duplicate vectors have already been eliminated. On a 75W Universal Laser Cutter, I was able to cut a sheet of 12 wave model spines in 12:30 minutes, so just over a minute per spine.
When you are ready to assembly the wave model, peel the protective coating from the acrylic.
Step 3: 3D Print Bases and Nut Holder
Using the Base STL file, you can print the two bases you need for the wave model. The STL is for a single base, so you will need to print it twice. The bases are designed to snugly fit 1/4" acrylic. If you decide to use a different thickness, you may need to tweak the design.
I generally print it with a layer height of 0.2mm, 20% hexagonal infill and 3 walls. Play around with it as you can probably get by with much quicker settings. The model prints in about 35 minutes on my Dremel 3D20 printer.
I made this simple wrench to hold the hex nuts while I thread in the lollipop sticks. I recommend 3D printing it too. Unless you have extra helpers to assemble, you'll only need one nut holder.
Step 4: Tie Twine Around Spine
Tie the string around the wave model at the lowest notch in the spine. Tie it as tight as you can without putting too much strain on the acrylic. I found that tying the knot at one end enabled me to pull and hold the first part of the knot tight with friction while I made the final loops to secure it.
Once secured, you can slip the string up one notch at a time to tighten even further. When you are done with the model you can loosen or tighten the string by sliding it up or down and see how that impacts the propagation of the wave.
Step 5: Mark the Middle of the Lollipop Sticks
We will need to know where the center of each lollipop stick to glue that to the strings. I've found it easiest to line up all the lollipop sticks and then mark a line down the middle with a ultra-fine tipped sharpie.
Next I'm going to design a simple 3D printable tray for marking the middle of the lollipop sticks.
Step 6: Measure and Mark the String
Starting at 1" from the inside edge of the acrylic spine, mark the string every 1/2" until you get to 1" from the other end. I ended up with 15 marks. You will glue the lollipop sticks later one. You can make them a little closer together, e.g. 1/3" inch, but too close and the hex nuts will bump, or wider as you desire.
You want to keep the 1st and last lollipop sticks an inch or more from the edge of the spine so that it can swing through without hitting the spine when the wave reflects at the ends.
Step 7: Thread on Hex Nuts to Lollipop Sticks to Make Lollipop Dumbbells
Using the 3D printable special purpose wrench (nut holder STL), thread the lollipop sticks into the hex nuts (one on each side). The 8-32 hex nuts were sized to screw onto the particular sturdy lollipop sticks I had. If you get different sticks for your model, you may need different nuts or you can hot glue the nuts to the end of the lollipop sticks.
Try to be as consistent as possible so each stick is balanced about the center mark you made earlier.
Step 8: Hot Glue Lollipop Dumbbells to Strings
Hot glue each lollipop stick dumbbells at the marks you made earlier centering the center mark between the two strings.
I've found putting a drop of glue between the strings and attaching the lollipop dumbbell and holding in place for 5 seconds works well. You may need to help balance it while you are attaching the subsequent lollipop dumbbells
Step 9: Send a Wave!
Once you've hot glued on your lollipop dumbbells onto the string, you are ready to send your first wave. Tap down one of the hex nuts and see how the wave propagates down the string. Does it reflect? What happens if you start it from the middle?
Does this wave model demonstrate longitudinal or transverse waves?
What would you do to improve this demo project?
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