If NASA plans to send robots to other planets, it's going to need some new designs: ones that are easy to land, easy to move around, and easy to fix. That means they probably won’t look like a bipedal T-1000 chasing the one hope for mankind. They probably won’t even look like the four-legged galloping critters Boston Dynamics is building. Nope. Those robots will look like a hexahedral tent stripped of its fabric.
With support from NASA's Innovative Advanced Concepts (NIAC) Program, engineers are developing just such a machine. They call it the Super Ball Bot: a robot made of metallic rods and cables that can extend and retract on command. It looks a little bit like a tangled mess of toothpicks and dental floss, but in space, that manipulable structure is ideal---it can expand and compress to absorb impact on landing, squeeze into tight spaces, and even move across the surface of a foreign planet in an odd crawling-slash-tumbling motion. The robot's creators, Vytas SunSpiral and Adrian Agogino, will have the latest version of the Super Ball Bot presented by members of their team at the IEEE International Conference on Robotics and Automation (ICRA) 2015 in August.
The pair first realized the potential of the squishable structure when they were playing with a six-bar baby toy, strung together with wire. Agogino threw it up in the air, and SunSpiral (yes, his name is SunSpiral) noticed how well it absorbed impact when it landed. SunSpiral recalls: "I said ‘Ah ha! It’s a landing robot!'"
It turns out the principle behind that baby ball has a name: Tensegrity. The term—a portmanteau of “tension” and “integrity”—was coined by the legendary designer and inventor Buckminster Fuller in 1955, to describe a structure of compressed components that create a net of continuous tension. (He first used it to explain Kenneth Snelson’s “X-Piece.") "Tensegrities have only rods and elastomers," says Agogino. By balancing compression and tension, the structure's elements distribute stress and impact throughout the structure, making it super-robust.
Agogino and SunSpiral built the Super Ball Bot based on Fuller's concept, with one crucial extra feature thrown in: the ability to retract or extend its cables. That's what really makes their robot ideal for space. "That combination of compressive and tensile elements makes form finding or shape shifting possible," says Agogino. A tiny tweak in the cable network's tension converts the robot from a rigid, resilient mass to a fluid, flexible form. When those cables tighten or loosen in specific ways, the robot’s legs move in a controlled direction. It’s not exactly graceful, but it works well enough, and avoids some of the major pitfalls of exploratory robots: balance and weight.
Most of all, the Super Ball Bot’s ability to collapse lets it fit in tiny spaces. When launching objects into outer space, every cubic foot matters, and it’s a great asset to be able to launch a robot that's essentially, as SunSpiral says, “a bundle of sticks.” The whole idea behind the Super Ball Bot is that you can cram it into a small space craft, drop it from a high elevation and land it onto a planet’s or moon’s surface like a bouncing beach ball.
NASA isn't the only group capitalizing on tensegrity. These kind of structures existed in nature long before Fuller slapped a name on them—in muscular systems of vertebrae, in tendon networks in hands, and all the way down to cytoskeletons in eukaryotic cells. “It makes a lot of sense why nature wanted to use this concept,” says SunSpiral. And it make sense for roboticists, too. Alice Agogino, the head of the Berkeley Emergent Space Tensegrities Lab at the University of California-Berkeley (and Adrian's mom), is currently working on a tensegrity robot inspired by the structure and flexibility of the human spine, in order to walk up stairs more easily. Similar bots could also have applications in search and rescue operations that require nimble movement.
The biggest difficulty in developing tensegrity robotics is actually a matter of perspective. “We’re accustomed to building rigid and linearly connected systems,” SunSpiral explains. “And we don’t have as many computational tools to develop tensegrity systems. [Super Ball Bot] breaks so many rules of conventional engineering.” But he's encouraged to see more and more of his peers tinkering with experimental designs that move away from humanoid movements and actions. Most of all, he thinks the advancements made in computational power have finally allowed many robotics engineers to test designs that were impossible to build even 10 or 15 years ago.
So in the future, if humanity ever does become enslaved by its robot creations, don't be surprised if those nightmarish machines look like something resembling abstract geometric art. The world will end not with a bang or a whimper, but a clank of metal rods.
