Tensegrity Stair Table

(cont. from Summary)

This sculpture is a combination between artistry and science: using tensegrity, this sculpture appears to be floating, showing a futuristic staircase complex. This structure could be used as a cup ledge or a tissue box stand, or it can just be decor. The dimensions of this structure is 6 in x 4.5 in x 6 in( my height is 6 in but can be adjusted to aesthetic preferences).

This was a team project, and my partner’s page can be found here: https://www.printables.com/model/377743-tensegrity-staircase

40lb fishing line: https://www.walmart.com/ip/Big-Rock-Sports-239370-Monofilament-Fishing-Line-40-lbs-Pack-of-4/53942451

Hooks: https://www.lowes.com/pd/Hillman-Brass-Screw-Eye-Hook/3199937?cm_mmc=shp-_-c-_-prd-_-hdw-_-ggl-_-LIA_HDW_126_Fastening-_-3199937-_-local-_-0-_-0&ds_rl=1286981&gclid=CjwKCAiA2rOeBhAsEiwA2Pl7Q7A7AWkY626UHzdtHH4Khu5PiE4nAmQe5EkHMI4MiYMeFgNDQY_GYRoCCUIQAvD_BwE&gclsrc=aw.ds

Problem Statement:  With a partner, you will design and create a single custom Tensegrity Structure of equal complexity or greater as the tables depicted below(as determined and approved by the instructor).

Parts List:

1 Bottom base (Long_bottom copy.3MF)

1 Top Base (Long_top copy.3MF)

4 railings (Long_railings copy.3MF)

1 Longer stair (Long_longer stair copy.stl)

1 Shorter stair (Long_shorter stair copy.stl)

Assembly instructions:

Tools we used: a hammer for punching the hole, pliers, small screwdriver, wire cutters for cutting the string, a ruler to measure the dimensions between pieces, 10 small golden hooks, hot glue gun, 40lb fishing line

Parts printed out:

1. Sand the four railings until they fit into the holes on the stairs

2. Make sure railings fit into the correct holes, then take the railings off for more space to work.

3. Punch holes in all of the marked spaces. Please refer to the picture below to see where the hooks should go, as well as how to punch the holes and attach screws.

4. Put the stairs in the bottom pieces and attach railings back on.

*the stair with the holes on the underside of fourth step from the bottom should be attached to the base that is not cut through, the stair with the holes on the underside of the third step from the bottom should be attached to the base with the through-hole

5. Tie the string to one of the hooks on the bottom step of a stair*. choose the orientation that you prefer (distance between the stairs that look good to you), and then tie the string to the other hook on the stairs. The structure should now be connected by a central string attaching the stairs to each other.

*How to tie the knot: 

1. Tie an overhand knot through the eyelet. Pull tight.

1. String A and B are the tail ends of the overhand knot in step a. Using the shorter  end (B) tie another overhand knot, this time around string A. Pull tight.

6. Tie all strings to the hooks on the top piece. This will make it easier to tie later on.

7. Start with the hooks 1 and 2. Hold the top piece to the right orientation, putting pressure on the central string and make sure it is taut and the top base is parallel to the bottom base. Loop the string through the corresponding hook on the bottom and tie a knot. Repeat for the other side.

8. Repeat Step 7, this time for hooks 3 and 4. The structure should have reached tensegrity by now. If not, tighten all the strings except the central string until the structure does not fall or twist when pressure is applied to the top of it. Make sure that all strings are taut and the bases are parallel with each other.

9. Snip all excess string for a cleaner look.

10. Tensegrity reached! (with failed prototype stairs balanced on top!)

Design changes

Initial Sketches:

We started out with a sketch that was going to look like two staircases stacked on top of each other. The inspiration was this image:

In this next picture, we made a sketch of what our tensegrity version would look like. The side profile is the smaller sketch on the side.

These were the more detailed sketches of the stairs with dimensions and railings. The restraints of the project was that it needed to fit in a 15inx15inx15in box, so the grid was mainly for figuring out the dimension of each step. The teacher said that two railing inserts would be more flexible than if all three railing poles went inside the stairs, so there are only two indents.

After checking in with the teacher, we decided our railings and stairs needed to be thicker so they would not snap. The bottom left one was our final sketch.

The teacher then wanted to challenge us by making us design a more complex design, so we added indentations onto the bases. We knew we wanted a flat top so we could balance things on top of it, so we chose to do an up-down-up-down type of indentations so the base would still be flat overall. We wanted the design to be very geometric to match the uniformness of the stairs, so we chose a square base.

Version 1.0

To save time and material, one of our bases was printed with cutouts of the design, which later made many challenges in the assembly. First, our stair holes were too wide, because originally we wanted it to seem like the stairs led up to the platform. This hindered our ability to connect the stairs and the bases, so we used a lot of hot glue to connect the two. In the pictures below, the circled part shows the globs of hot glue needed to stabilize the structure. Tensegrity was reached, but we had to hold the cut-out base and the stairs together, and it was very fragile.

To fix this, we decided that we would not have the cutouts, and we would eliminate the space between the stairs and the side of the inside hole by making the hole smaller. Instead of three contact surfaces, the new one would have four contact surfaces. Since the fit was not snug in the draft, the length will be decreased by 0.02cm, and the width would be reduced to 0.79cm (thickness of the stairs + 0.04cm). We also made the aesthetic choice that the top base would be closed off so the stairs wouldn’t be visible from the top (example showed in Version 2.0).

this rectangular hole would be reduced

Then, to save material, we decided on making the square top a narrower top and cutting the width of the stairs by 1.74 cm (new width was 5.28 cm).

We also needed to sand down the railings to fit the stairs, so we enlarged the stair holes by 0.04cm on each dimension so the railings can fit inside. This would need to be done on both the long and the shorter stairs.

Version 2.0

Version 2.0 was virtually only a little bit less of a disaster than Version 1. The most noticeable difference was that the bases were rectangular and the stair hole was smaller, like the changes we proposed in the section above, but the whole base was also thinner than we expected, to save material and time. Another change was that the bases now had teardrop shaped holes, also to save material. The picture on the left is the bottom base and the right is the top base, without the through-hole for aesthetic reasons.

The railings fit inside the new stair holes fantastically. However, the stairs did not fit in the stair holes at all, so we spent an entire class sanding the stairs and clipping the inside of the hole with a broken wire cutter blade and the nib of a hot glue gun. The thinness of the base made it even harder for the hole to grip the stair of the base, which meant we had to sand even more.

the hole being too small for the stairs

sanding the stairs and enlargening the hole

Final version thickness vs Version 2.0 thickness

Our teacher then advised us to just fill the hole with hot glue to make it work. We didn’t get enough time with it to assemble it completely.

Version 3.0

Since we were running out of time in the course, our teacher surprised us by printing two full sets of new parts! This time, we were able to fit the stairs right in the stair holes without sanding. The stairs were changed from being completely flat to being curved to assist in the fitting of the hole. The railings on the other hand did not fit anymore, so we had to sand those down a little bit, but it was way better than sanding the stairs.

The base was also returned to its original thickness, which gripped the stairs better. Then, another change was that instead of having both strings be connecting from the bottom of the stairs to the base:

We changed it to this on one side:

For more stabilization.

Tensegrity was reached with little changes besides the sanding of the railings!