Popsicle Stick Tensegrity Table STEAM Activity - Easy to Assemble!

This is part of a series of Instructables detailing free science kits and activities developed by the spectrUM Discovery Area in Missoula, MT. The kits and activities are for use at home, in the classroom, or in a distance learning setting with teachers.

For more on how our museum shares these activities with students and teachers, see this video on YouTube.

Tensegrity tables and other structures seem to be all the rage these days. They can be relatively simple to build and the effect is wonderful - they look impossible and appear to defy gravity! We thought we would get in on the fun by developing one to distribute as an engineering science kit to kids around the state of Montana. In researching how to go about this, we found a number of other Instructables that demonstrate how to use hot glue, string and popsicle sticks to create a structure that uses tension and integrity to appear to defy gravity. See minniep3's version here and Harman1796's version here.

For our assembly, we wanted to remove the hot glue and need to cut or drill the popsicle sticks, as well as make it easier to build for younger learners that don't have a lot of manual dexterity. The use of rubber bands also takes out some of the tricky aspects of getting the string tension just right with other designs. Follow along to learn how to assemble your own gravity-defying structure and test how much weight it can hold!

This Instructable is entered into the Anything Goes contest, so vote for it if you find it useful or inspirational.

Supplies

• 6 Regular 4-1/2" x 3/8" popsicle sticks (jumbo ones or tongue depressors might work but have not been tested with our custom clip). We like colorful ones from Discount School Supply.
• 6 glue dots or a small amount of wood glue/hot glue or tape.
• 6 mini binder clips - generally the smallest ones you can find at office supply stores
• 3 rubber bands, size #32
• 1 rubber band, size #8 (size #10 works but not as well)
• 2 3D-printed clips
• A piece of paper
• A pencil
• Scissors

Step 1: Advanced Preparation: 3D Print Center Clips or Plan Alternative

If you are doing this in a classroom with students, you'll want to 3D print the attached clips that we designed specifically for this purpose in advance. Each student will need one set. They are pretty quick to print, our printer does a set in 15 minutes and a batch of 10 in about an hour. PLA works great but other strong, stiff plastics like PETG or ABS work as well, low resolution like 0.38mm-1mm is fine and relatively low infill like 10-15% is acceptable.

We spent some time and a number of iterations to design these clips to make our kit easy to assemble for all ages and remove the necessity to modify popsicle sticks for the center support of the table. If you don't have access to a 3D printer, don't worry - you can cut or break a popsicle stick in half at the center at a 45-degree angle to glue down. You'll need to cut or drill a notch on the rounded end or get creative with glue dots/glue and the rubber bands or even a short piece of string where they attach in the center.

If you are planning to use this activity with older students (grades 8-12), it would be a better challenge for them to design this central piece anyways! It would be a great way to introduce how to use a protractor to get the right angle, etc. One tip I have is to mark where you would want to separate the popsicle stick with a pencil, hold that line along the straight edge of a table, then simply break it off - they are difficult to cut with scissors and somewhat dangerous to cut with a razor blade for students.

Step 2: Make Two Triangles

Our tensegrity table is essentially two equilateral triangles, one suspended on top of the other. To start, take three of your popsicle sticks. I like to add a glue dot at one tip, then lay the other over the top of it at about a 60-degree angle. Add a glue dot to the other end of either, add the third popsicle stick. Complete the triangle by adding a third glue dot at the last point of your triangle. You can substitute Elmer's white school glue here, hot glue, or even a piece of tape.

Make a second triangle with the other three popsicle sticks just like the first one you made - they will be exactly the same. It's nice to have the multicolored popsicle sticks to add some color to the structure if available, you can also take washable markers and color your craft sticks or draw on them if desired.

Step 3: Trace and Cut a Top Platform

To make it so you can easily stack items on your table, you'll want to cut and trace a top piece before proceeding. You can use paper, cardboard, cereal box, etc. I like to take one of the triangles we created in the first step and trace the outline on a piece of paper or cereal box. Then, take a pair of scissors and cut out the triangle. Note - if you line up one of the edges with an edge of the paper, you have a bit less cutting you need to do!

Step 4: Add Binder Clips to Each Triangle

Now that we have our top and bottom made, add a binder clip to every tip of each triangle, for a total of six binder clips. If you made a paper or cardboard platform, you can simply lay it on top of one of the triangles and let the clips hold it in place instead of needing to glue it down, etc. It's not shown in some of our photos going forward so we could illustrate assembly, but this is the best step to add it in.

The binder clips are performing an important function here - they keep the triangles sturdy and the popsicle sticks stuck together properly, while also making a nice hook for our rubber bands to attach to.

Step 5: Add the 3D Printed Clips

The real "guts" of the tensegrity table are these two clips. They just need to be attached such that the little notch of each is at the center of the triangle. If you are making your own from something else, be ready for some trial and error.

I find it best to attach one clip at a vertex of one of the triangles very close to where the popsicle sticks are glued and clipped together, and the other to the center of the other triangle's sides. See the above photos. They simply clip in place, no glue necessary. If they slip a bit, you can add some tape as a shim or just glue in place. If they are too tight you can remove some material from the interior with a razor blade or heat slightly with a hair dryer so the plastic softens, then attach to the popsicle stick. I designed them to be somewhat compliant and haven't yet found a popsicle stick they wouldn't properly attach to.

Step 6: Add Rubber Bands and Assemble!

Now, take the three #32 rubber bands and place one under each binder clip of one of the triangles as shown. This is the easiest way to do the tricky part of assembling this whole contraption. Take the smaller #8 rubber band and hang it in the notch of the clip on this same bottom piece.

Take your other triangle and clip the notch over the little rubber band in the center and push down a bit to stretch the rubber band. Then, carefully attach each of the three other rubber bands over the top of its corresponding binder clip on the top triangle piece. You need to hold on to the whole thing while assembling. Don't get frustrated if this part takes a few tries and minor explosions to get right! If you're having a hard time visualizing how this all goes together, see the photos above from lots of angles and think about how you might best orient things to get this all assembled correctly.

Once all rubber bands are hooked in place, your table will magically be floating in the air! You can make small adjustments to the table so that the top triangle sits directly over the bottom one. You might need to wiggle the 3D-printed clips around a bit so they meet exactly in the center, and ensure that the rubber bands are around the little silver wires of the binder clips and not the black body part.

Step 7: Test Your Table's Strength

Now it's time to see what this thing can hold. Start with lighter items like LEGO mini-figurines or small toys, and work your way up to heavier items. If you have something a bit heavier and bigger - like our 3D printed model of the University of Montana's Main Hall, you'll need to get the center of gravity right over where the rubber band in the center is - if it's too far off to one side or the other, it pulls the whole thing too far to that side and the tension of the rubber bands becomes too far off balance, eliminating its integrity. We also have some small weight sets that we can add incremental 50g weights to (up to about a pound/500g) to test out the max capacity, which is a handy way to increase the load until it fails if you are looking to test that.

If you add too much weight or it's not balanced in the center of the table, it will fly apart - don't worry, though, it's very easy to put back together again and again!

Tensegrity structures like the one we've made here work by having a bit of tension pulling in all the right places evenly to suspend pieces in an orientation to each other to create a structure that has integrity. There is an equilibrium of the tension of the three big rubber bands pulling the two platforms together (like the three legs of a stool) and the little rubber band in the center pulling them apart from each other. In our version, the three rubber bands are pulling down on the top triangle equally at all three corners. The center rubber band is pulling the top platform up to suspend it from the hook attached to the bottom platform. If any single one of these four rubber bands gets stretched too far or gets too slack, the whole thing collapses because the tension of the others pulls on the structure unevenly. They all work together to pull the structure into place in three dimensions.

For a great description of how tensegrity structures work and a few nifty applications, see this video on Youtube from Steve Mould or this one from the Action Lab.

Step 8: Questions to Ponder

Here are some things to think about and ask your students about when facilitating this activity in the classroom:

• A bicycle wheel is an example of tensegrity in everyday use - the hub is suspended in the center of the rim by the spokes pulling equally in all directions away from it towards the rim. Can you think of some other examples?
• You can use string or wire instead of the rubber bands in our model. What things might you need to consider when getting them to the right length and tension? How might you attach them?
• There are other tensegrity structures that you can build, some of which are just about as simple as ours and some which are much more complicated. See this website for some great examples of other structures.
• NASA is designing robots - like the Super Ball Bot - that are a tensegrity structure which varies the length of the cables to "walk" across a surface. Can you design something similar that uses this concept to move? What might be some challenges?
• If you were to build a bigger version of this table, how might you go about designing it? What materials would you use?
• It's possible to make 2-dimensional tensegrity structures similar to ours. How might they look? What things might need to be modified or simplified to make them work in only two dimensions instead of three?
• What was the hardest part about building this structure? How might you change things to make it easier for yourself or others to assemble?

If you'd like to print the instructions for this activity for a classroom or yourself, see the attached .pdf on this step to download and print. This is laid out for short-edge printing to fold in half for a booklet that can be stapled (or not).