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Instruments Of Change: The Engineering Behind Bjork's Musical Robots

We take a look at some innovative individuals who don’t follow the usual rules when it comes to equipment. Why buy instruments when you can make your own?

Without the tools to create, where would we be? Listening to the sound of one hand clapping, probably. In this column we’ll be looking at people who invent their own tools—be they musical, artistic, photographic—any sort of bespoke equipment from innovative builders of all disciplines and ages in a celebration of the fine art of invention. This week: Andy Cavatorta and his Gravity Harps

Bjork recently started her latest world tour at the Manchester International Festival. Wearing a giant ginger wig, she took to the stage with a 24-piece all-female Icelandic choir, a Tesla Coil, and assorted multimedia musical trickery. Watched by an audience that featured as many science as it did music journalists, the spectacle explored the concept of biophilia (which sounds wrong, but is actually, according to Wikipedia, “an instinctive bond between human beings and other living systems.”) and judging from the coverage we’ve seen, it apparently lived up to the hype.


This hybrid of nature, technology and music moved one journalist to say “It must be one of the most complex pop shows ever”, and in among the complexity was Andy Cavatorta’s 10ft tall acoustic, robotic pendulum string instruments, also known as Gravity Harps. What are they? Where did they come from? They may look like alien robot totems, but we caught up with their creator to get the real story behind these wild inventions.

The Creators Project: Bjork's renowned for her eccentricity, so when she approached you to make her some musical robots, did you see it as an excuse to experiment and go crazy?
Andy Cavatorta: At first I felt intimidated. When it comes to potential collaborators, the world is her oyster. Check the history—Gondry, McQueen, Cunningham, etc. On one level, I was just hoping to not fall too short of the high expectations. But yeah, I was leveling-up what I thought was possible. Machines that weave musical scores like spiders weave webs, and others that play them like player pianos. Playing strings with water. And of course, the pendulums.

What made you want to combine the properties of pendulum and harp?
Bjork already wanted to do something with a big pendulum and even had the song “Solstice” in mind. She wanted a single huge pendulum to play out the notes of the song. I loved the simplicity of it and how graceful the single slow pendulum would be. But I could never figure out an aesthetically uncomplicated way to do it. Part of the challenge was that the song is full of different phrase-lengths and time signatures and the pendulum is going to swing in just one rhythm. Of course there are complicated ways to do it. But the simple beauty would be far gone.


Demonstration of the instruments on set in Manchester, UK

This was a collaborative effort, so how many people did it actually involve?
I was lucky to have a great production team, mostly friends or friends of friends. I had to have a certain kind of obsessive maker for this. Time was not on our side when we thought we’d start in September 2010. Redesigns made that slip to January 2011. Then our workshop fell through and we suddenly needed to find another. It was mid-March before we were in production. To finish in the three remaining months, we were going to have to work about 100 hours a week. Nobody was going to do this just for the money. There are obsessive makers, who build all day, then go home to make more cool stuff. You can spot them right away when you look at their portfolios. They’re outliers and they’re the ones you want to work with. But they’ll only do it if they LOVE the project.

Marina Porter came on first. She’s a sculptor with great patience for details and fine woodworking. She also has the best musical ear of anyone I know.

Doug Ruuska is a very experienced fabricational jack-of all-trades and adventurer. He also seems to truly enjoy heights and danger, which was a big plus on this project.

Karl Biewald is a designer and mechanical engineer. I was totally sold by the slow-motion car crash sculptures he’d helped create.

Dr. James Patten is a designer and engineer from out of the MIT Media Lab. He made the robot brains. And his scientific approach to problem solving made him the right guy to figure out how to control the unruly pendulums.


Finally, I asked designer and roboticist Ryan Wistort to join me in Manchester as the official robo-sitter for the shows. Things got tough the moment we got there and found we had to create new support structures to fit the venue. He stepped up with metal fabrication, woodworking, embedded system programming, etc. He also kept his cool when I was a sleep-deprived zombie.

How many different component parts did it involve?
Since it’s a robot, there are mechanical, electronic, and computer programming components. Plus the acoustic instruments. A lot of time went into important components the audience will never care about. We invented silent, vibration-insulating bearings of nylon, sorbothane, and milled aluminum to protect the harps from the vibrations of the motors. I wrote an interface full of live graphs to help us understand the relationships between each pendulum’s amplitude, phase and natural period. We created adjustable bridges to correct for the eccentricity of the harps as they warp with changes in temperature and humidity.

Boooooring. But oh-so-important.

How long did the project last from the initial concept to completed instrument?
It’s a bit of a blur. I developed concepts and prototypes for about 7 months. We were in production with the Pendulum Ring for about 2 months. The final product, the Gravity Harps, went from napkin sketch to final prototype in about 30 days. We were already burnt out from the Pendulum Ring build process. So we were just pushing through exhaustion all day, every day. And sometimes all night, too. Atop scaffoldings with power tools and exposed wires… It was kind of dumb and I’m glad we’re all still more-or-less intact (though Doug did pass out with exhaustion while operating a band saw). That could have been tragic. But he got off with just a broken tooth and some head lacerations.


Projects like this—where you start not knowing if the solution is possible—feel to me like navigating a perilous jungle. How deep does it go? Is this a dead end? How wrong is our map? You just have to keep going and going until you find the end.

Bjork's spoken about wanting to "explore nature" on her new album. Did you attempt to manifest that concept into the instrument or was it already complicated enough?
Bjork’s idea of nature wasn’t limited to living things. She wanted to include forces of nature. In this case, the pendulums are a manifestation of gravity. And also of natural oscillators—which change one form of energy into another and back again.

The instruments performing with Björk for the song “Solstice”

You've said on your website that it takes a lot to explain how the Gravity Harp plays a complex song. Any chance you could attempt to summarize that for us?
There are four pendulums, each with a cylindrical harp on the end. As each pendulum swings through its lowest point, a single string on its harp gets plucked. The harp is cylindrical and can rotate, so any one of its eleven strings can be played by facing it to the plucker. There is also an ‘empty’ string position for playing rests.

The four pendulums all have the same periods. But their phases are offset so they play in order 1-2-3-4-1-2-3-4. They could also play other rhythms. But this metronomic setup works really well for the song “Solstice”.

I don't know if you're going to hate me for saying this, but in the video of the instruments on stage with Bjork, they remind me of wood chimes. Maybe this is hinted at by the complex Oriental sound. Did you have a specific idea of what sound you wanted to produce from the very beginning or was it part "voyage of discovery"?
Ahhh, the plinkiness. I’ve since modified that sound by changing the pluckers, so they pluck more gently. The harps now have a much more sweet and resonant sound. In my first meeting with Bjork and her producer, Damian Taylor, I was told that they already knew what these yet-to-be-envisioned instruments sounded like—in that they’d already composed pieces for specific timbres. “Solstice” used a harp-like sample that was undoubtedly heavily altered by Damian. But there seemed to be a mandate that the instrument to play “Solstice” should sound like a harp-like.

Of course the only thing that really sounds like a harp is a harp, and we weren’t going to be using a bunch of pre-built harps on this experimental instrument. But with some experimentation and prototyping, Marina and I discovered how to get that sweet, resonant, harp-like timbre by having the strings meet the soundboard at an angle and by using multiple sympathetic strings.

Beyond that, this entire process has been a voyage of discovery.