Shuriken Tensegrity Structure

Summary Continued:

 It can even support up to 3 pounds of weight, so feel free to use it as a phone holder, beverage stand, or whatever else you want. With dimensions of about 14cm x 14cm x 10cm, it’s perfectly portable and easily fits wherever you want.

Link to my partner's page:

Lesson Plan and Activity:

For this project, our task was to design and create a single custom Tensegrity Structure with some amount of complexity while also focusing on collaboration with a partner and utilizing the features of Solidworks.

Parts List:

Modeling Instructions:

Top/Base:

• On the front plane create a constraint box that is 15cm x 15cm with the origin in the center
• Draw a construction circle centered on the origin with a radius of 5cm
• Draw a horizontal and vertical construction line of symmetry that goes through the origin
• Draw 2 more construction lines that go through the origin at 45-degree angles with the other lines
• Draw a construction line starting from the edge of the circle that is perpendicular to the circle and reaches the edge of the constraint box.
• Connect lines from the top of the extruding construction line to the points adjacent to the circle
• Use a construction line to connect these two new points and make them symmetrical.
• Use the circular sketch pattern tool to copy this extruding triangle around the circle 8 times evenly spaced out.
• Use the 3-point arc tool to draw an arc between the points of two triangles next to each other. The arc should point toward the origin.
• Again, use the linear sketch pattern to copy the arcs 8 times around the circle, evenly spaced out
• In a new sketch but on the same front plane, draw a construction line from the tip of one triangle to the end of the triangle opposite to it
• Draw one construction line centered on the origin with a length of 6.5cm and another one with a length of 7cm
• Draw a 1.03 cm x 0.78 cm rectangle centered on these new anchor points on the construction line

Arch:

• Create a constraint box that is 15cm x 15cm with the origin in the center
• Use the  parabola tool to draw a parabola with legs 6.5cm apart
• Then make a 1cm x 0.75cm box down from each side of the arch using the line tool and connect the parabola on the inside which 2 lines on each side meeting at a horizontal line at the top.
• Then extrude the arch 0.75 cm by using the extrude tool
• Then make an engraving of your name onto the arch by using the Sketch text tool, after typing the desired name put it on the arch 
• After, select the name and use the Cut-Extrude tool to cut the piece by 0.1cm

Assembly Instructions:

1. Fit the triangles into the holes of the bases

2. Use a screwdriver tip to poke a pilot hole/divot into the spots where the hooks will go. Don’t forget to put hooks on the arcs as well. You may need to use something heavy to hammer it in a bit to create a big enough divot.

3. Screw 4 hooks into their corresponding triangles with pliers or fingers (None of the hooks should be adjacent to each other, there should be one spoke of the base between each one. We found this process easiest when we held the hook with pliers and placed the tip in the hole, then proceeded to spin the base on a flat surface, therefore, screwing the hook in by spinning the base.

4. Tie a string with a square knot connecting the hooks of the arcs together so they interlock. Make sure they are close enough together that the top of each arc won’t interfere with the bases when put together.

Instructions for square knot: First cross the left string over the right. Next, loop the left string through the hole. Now, repeat the first two steps but cross the opposite string on top.

5. Connect the arcs to their bases by placing the peg in the corresponding hole of each base with a friction fit.

6. Tie a string of medium length to each of the six hooks on one of the bases. The string should hang loose at one end.

7. One by one, tie the hanging end of each string to the corresponding hook on the other base. The tension in the strings should cause the base to stand flat/horizontally. You may need to go back to each string and tighten them after.

8. Cut off the excess string from each knot.

9. Celebrate your Tensegrity Structure

Design Choices: 

The first step in our design process was creating a preliminary sketch in Google Draw.

Next, we moved to paper and pencil and drew a more detailed sketch using rulers and protractors.

We realized we could scale up the size of the overall sketch while still keeping it in the 15 cm by 15 cm constraint box so we redrew the sketch larger to fit itself better. This new sketch contained the holes into which the pegs of the arches would fit when assembled.

After finalizing the sketch, we listed out a step-by-step plan to instruct us during the assembly in Solidworks.

Now, it was time to move over to the computers to transfer our sketch onto Solidworks, the program used to model 3D designs to be 3D printed. I worked on creating the model for the base.

Meanwhile, my partner worked on creating the model for the arch.

Once both models were complete, it was time to add engravings to detail the pieces. We made a copy of the base part, so we both could make our own design.

Next, we decided to extend the arches from a semicircle shape to a parabola to give the structure some height.

I then created some simple engravings on the arch and made an extruded cut of our team name, DOE, on the top.

After all the parts were done, both bases and the arch, we opened a new assembly in Solidworks to mate everything together and see if it would fit when printed.

Then, once the parts were mated in the correct orientation, we added hooks and strings as placeholders to see what they would look like when it was fully constructed.

The parts were printed, and it was time to construct version 1.0 of our tensegrity structure. We laid out our parts which consisted of 2 different bases, and 2 identical arches.

We followed our construction instructions and finished with our first version of a tensegrity structure.

The first problem we ran into was the hooks were repeatedly slipping out of their holes requiring us to take the structure apart and apply glue to the hooks before rescrewing them in.

Another issue with our structure was that it could not support much weight. Anytime too much force was applied to the top of the structure, the inner middle string would stretch causing the outer strings to lose tension and overall lessening the structural integrity of the table.

The last problem had to do with the outer, support strings. Originally, the structure was designed to stand where the arches were perpendicular to each other; therefore, the bases would be slightly off-kilter from each other. Due to there only being six spokes on each base, the strings would have to reach at a diagonal from the top hook to the bottom hook.

However, the physics of the structure forced the strings to stand upright which pulled the arches to a non-perpendicular angle.
 

To stop the inner string from stretching from too much weight, we changed the knot. Rather than tying the string to each hook separately, we looped it through both hooks and tied a square knot in the middle. This made it so that when pressure was applied to the top of the structure, the force would tighten the knot instead of stretch the string.

After realizing what needed to be improved, we listed out the changes we needed to make for version 2.0 and got to work in Solidworks. The first change we made was redesigning the bases to have 8 spokes rather than 6. The first advantage of this change was the strings could line up with both bases so they wouldn’t be at an angle and the arches would stay perpendicular. Also, we now only needed to use four hooks for each base (one on every other triangle) instead of the previous number of 6 hooks.

To solve the problem of the hooks slipping out of the bases, we figured out we had to increase the infill. Unfortunately, it was too costly to up the infill for all the parts to 100%, so instead, we cut all the way through the base on each spoke a triangle shape. Then, we created a separate part that would be added to the assembly and would fit into the base with a tight, friction fit. This separate triangle piece would be printed with 100% infill so the hooks would grip to them better.

There were two modifications made to the arches. Firstly, we changed the shape slightly so there was a horizontal on the inner part of the peak. This allowed the hook a flat surface to screw into compared to a curved one as before. We also stretched the arch a bit to make the structure taller and sleeker.

The base was also slimmed down from 1.00cm to 0.75cm for a sleeker look.

Another addition to the bases was using the mirror tool to copy the designs onto both sides of each base so one side wasn’t bare.

The final change was printing the parts out in black and red instead of grey.

Once these new parts were printed, we followed our improved construction instructions and put together the 2.0 structure.