Rope and Sound Interactive Tensegrity Sculpture

A unique interactive musical harp using electronic sensing rope technology. 

This piece originally appeared as part of the Extreme Textiles exhibit at the Smithsonian's Cooper Hewitt National Design Museum in 2005.  During 2006 it was installed in the main lobby at Pixar.

This piece is currently seeking a new home in a museum or similar location!
Please email dan-at-MonkeyLectric-dot-com if you can help.

HOW TO PLAY THE HARP

• Grip any blue rope near the center of the rope
• Pull hard to make a sound!
• Each rope makes a different sound (listen to the mp3 file below)
• Watch the display screen when you pull

ABOUT

• Conductive fibers are braided with traditional fibers to produce a patented rope technology that is capable both of carrying a load and monitoring the weight of that load.  The rope acts as its own strain gauge, monitoring tension constantly while the rope is in use. In this installation, changing the tension in the blue sensing ropes creates an electrical signal that modulates the music that you hear through a synthesizer. Just as the human muscular-skeletal system is a tensegrity of muscle and bone, the ropes and aluminum tubes form a tensegrity of tension and compression, pushing and pulling, weightlessness and gravity.
• Based on Tensegrity structures. The three main struts are held in place only by the tension of the ropes, they are not attached to each other or to the floor. A "standard" three-strut tensegrity of similar form has nine ropes required to hold it up. Here we have replaced each of those nine ropes with a spline of twelve, resulting in 108 total ropes. The resulting structure is surprisingly sturdy, it can easily support hundreds of pounds from the top end of each main strut with negligible deformation.

SIZE

• 9 feet high, 8 feet wide, 8 feet deep (dis-assembly is possible for transport)
• approximately 300 pounds
• three main struts are 12.5 feet long, 5.5 inch diameter.

MAKE YOUR OWN!

You can build your own non-musical model of this structure in just a couple hours.  All you need are 3 sticks, a roll of string and a drill.  (see the last step of the instructable)

This instructable is intended to show you the inner workings of the sculpture and some of the challenges involved in building it. 

The exhibit features our patented electronic sensing rope.  I visited a yacht rope manufacturing facility and worked with their engineers to produce the rope specially for this project.  The rope integrates electrical fibers into a standard polyester double-braid yacht rope.  Below are some photos and videos of this process.

Rope braiding machines are fun to watch!

The electronic sensing rope is cutting edge technology, it had never been done before this exhibit.  So we tested our electrical measuring system end-to-end before proceeding with the tensegrity build.  Here's some videos of the testing:

The tensegrity structure we envisioned had never been built before to our knowledge.  At first we weren't even sure it was going to be stable, and then we weren't sure it would be viable to construct even if it was. 

I started by making models.  The first model used 3 foot long wood rods and only a small number of strings.  It was similar to a normal tensegrity shown in the photos here.  It seemed to work so then we made the 2nd model using 12 foot long wood 2x4's.  The 2nd model we strung together using standard 1/4" yacht rope with about half as many rope segments as the final.  This helped us arrive at a mathematical model of the design, and also gave us a good understanding of the construction challenges.

Our structure replaces each of the single ropes shown in the "normal" tensegrities below with an entire spline of 12 ropes.  From building the models, we learned that tensioning all the ropes equally was difficult.  We needed to build a tensioning mechanism into our structure.

In our structure, each rope starts inside a tube, goes through 2 holes in a 2nd tube and then to a tensioner at the center of the 2nd tube.  So, there are 3 holes for each rope total.

Making a model like this can be done in a couple hours, you can make a small one yourself at home!  See the last step of the project.

• The 3 main tubes are 12.5 feet long and 5.5 inches diameter.  They are made from 6061 aluminum with 1/4" thick walls.  Our local metal supplier didn't have too much trouble getting them.
• The sculpture uses 108 total ropes. Each rope passes through 3 holes total, so we end up with 108 holes per tube.
• The tricky part is to calculate the location of all the holes.  The holes are spaced equally along the length of the tubes, but the angular locations need to be calculated using some non-trivial math.
• After calculating the exact angular position of every hole, we translated that into a machining jig.  The machining jig was a semi-circle of wood that cradled the main tube.  The semi-circle had angular marks on it showing the position of every hole and distance from the end of the tube.  So, we positioned the jig and tube under a drill press and went down the length drilling all the holes at the proper angle.
• Then we deburred all the holes.  Many of the holes have black press-fit plastic glands also, so the rope slides better.

• Each main tube has a tensioning disc at its center.  The tensioning disc is about 10 inches diameter and made from 3/4 inch thick aluminum plate.
• Each tensioning disc has 36 holes where ropes will attach to it.  One end of every rope attaches to a disc.
• We cut the tensioning discs and their holes with a CNC waterjet cutter
• The tensioning discs are pegged to the main tubes with 5 steel pegs
• Each main tube also has a metal plate at its foot.  These are screwed into the main tube.
• Each main tube has an additional 12 holes near the tensioning disc where we will make electrical connections to the sensing ropes.  The location of these is cosmetic only.

The tensioning hardware uses:

• 8" long threaded steel U-hook
• locknut
• spherical washer pair.  this allows the hook to exit the plate at an angle up to 5 degrees from straight, without bending the U-hook.

We'll tie the ropes to the threaded U-hooks, and then we can tension them by turning the locknuts

3 feet are a simple round disc of aluminum with 1/2" of rubber glued to them.

We also made lead weights that slide inside the base of the main tubes for extra stability.  This proved to be totally unnecessary but we had already made them by the time we figured out we didn't need them.  To make the weights we cut a 2 foot section of the same tubing we used for the main tube.  We capped the ends and filled it half way with molten lead.  no joke!

After the machining but before any of the electricals were installed we did a test assembly with all plain rope to make sure there were not any problems.  Actually i'm sure there were some problems but I don't recall what anymore.  So we fixed those problems and went on to the final assembly next..

The soft-circuit sensing ropes need to connect to regular wire at each end.  We create a flexible and high-surface-area connection using a segment of copper braid.  Watch the photo sequence with photo notes to see how it is done.

• Each main tube has one end of 36 ropes installed in it.  12 blue sensing ropes and 24 black non-sensing ropes.
• By only attaching 1 end of the ropes, each of the 3 main tubes is separable for transportation purposes.
• The photos are looking into the ends of the tubes.
• The electrical wires from the 12 blue ropes all go to the bottom end of the main tube.

the 2nd end of the rope doesn't get attached until we assemble the sculpture, but we prepare the wire connections for it now.

A single black wire enters at the bottom of the main tube, inside the tube it splits to 12 wires, 1 for each of the 12 connection holes near the center of the tube.

The end of each black wire has an insulated spade connector on it, and the 2nd end of the blue ropes have a mating connector.  When we assemble the structure we'll just plug them together.

We used brass fittings at the 12 connection points.

The control box is disguised as a spool of rope, haha!  Inside it includes:

• mini-size Windows XP computer and 15" LCD monitor
• 64-channel Data Acquisition (DAQ) card - we used a Measurement Computing PCI-slot card.  It has 64 analog inputs and about 1M samples/second.
• Wiring and electrical interface between the sensing ropes and the DAQ card.
• Power distribution to the computer, monitor and speaker

There are 36 blue sensing ropes total.  Each has a wire going to a separate sense channel on the DAQ card.

to set it up, we made a wooden jig to hold everything in about the right place.  We need to attach 12 of the ropes before it will self-support in the proper shape.

Check the photo-notes for more.

Although the strings make sounds when pulled, we also put a LCD screen to show a more detailed view of the signal data.

On the computer we have custom software that translates the data from the DAQ board into MIDI events.  The MIDI is sent to Ableton Live which plays samples from a set of 36 out the sound card and to the speaker.

One big lesson I learned:  if you want to be able to show your work a lot, it better be easy to transport and set up!  Once assembled this piece is too big to fit through most doors.  It takes 2 people about 10 hours to assemble it and another day to break down because you need to tie and untie all 108 ropes.

If you have big doors at both ends It can be transported fully assembled.  My next sculpture I planned much better for transport - that one sets up in 90 minutes.

Colin Bulthaup, Squid Labs - Design
Dan Goldwater, Squid Labs - Design, Electronics, Software, Rope, Project Management
Saul Griffith, Squid Labs - Design, Structural, Mechanical, Rope
Ben Recht, MIT Media Lab - Design, Sound
Eric Wilhelm, Squid Labs - Design
Matilda McQuaid, Cooper Hewitt National Design Museum


original project page:
http://squid-labs.com/projects/tensegrity/index.html

You can make your own non-musical model of this structure at home!  It only takes a couple hours. 

• Find 3 straight, equal length wood sticks
• Drill a row of 12 (or 16) holes into each stick, equally spaced.  your holes should be just big enough for your string, so that if you put a knot in the string it will not pull through the hole.
• Drill 2 more rows of 12 (or 16) holes right next to the ones you just made, so you have 3 rows total.  this is because 3 different strings connect to each stick at each location.
• Cut 9 equal-length pieces of string about the length of your sticks
• have a 2nd person hold the 3 sticks in about the right position (see photos below)
• attach the 9 pieces of string like in the small model photo below.  its ok if things are a bit loose and sloppy at this point.  now you've built a basic tensegrity!
• once your basic tensegrity is stable, you can start making the special version like ours.  look closely at the larger model photo below that i'm standing next to.  the purple rope is a single continuous piece, fed through holes in the wood.  it's a bit like lacing a shoe.
• you need 9 long pieces of string, each long piece will create a laced spline pattern to replace the corresponding short piece of string you used to make the basic tensegrity.  to make the structure rigid you will need to lace these in a bit loose first, then go around tightening them.