Servo - May 2015

bots IN BRIEF

SERVO 05.2015 23

TOSS ME A SUPER BALL BOT NASA’s Super Ball Bot has to be one of the weirdest, yet most effectively innovative robot designs yet. It’s a tensegrity structure: nothing more than a bunch of rods connected by a bunch of cables. It’s almost certainly not what you would picture when you think of a robot — much less one that’s intended to head into space. They’ve been working on this project at NASA Ames Research Center, through NASA’s Innovative Advanced Concepts (NIAC) program.

The primary advantage of tensegrity structures is that they are excellent at distributing forces. Since there is no rigid connection between any of the structure elements of the robot, they’re easy to pack, easy to unpack, and extraordinarily resilient to external forces — since any external stress gets absorbed across the entire structure of the robot. This means you can drastically reduce the mass of the robot and still end up with something strong enough to meet your mission requirements.

Super Ball Bot also features tunable stiffness. By increasing or decreasing the tension on the cable network, the bot can transform from a nearly rigid structure to a squishy and compliant pile of interconnected sticks. The sticks are the muscles of the robot, containing motors that wind and unwind the cables. By making the right cables at the right lengths at the right times, the sticks can make the robot move.

Saying that Super Ball rolls might be a bit optimistic, but it can move in any direction, has no problems with rough terrain, and can even make its way up hills. If you do somehow manage to break something on the robot, it can keep itself going even after 75 percent of its actuators are non-functional, or even if a cable snaps.

For the last year or so, NASA has been working on a much larger and more complex version of the robot, called SUPERball. SUPERball has 12 actuators (the final robot will have 24) — enough to really explore how to make the robot move effectively. It’s also large enough that a scientific payload can be suspended inside to see how it fares, and modular to be able to test out different structural configurations.

Long term, a robot like this could be perfect for exploring a place like Titan

(Saturn’s largest moon) where the atmosphere and relatively low gravity means that you could drop the robot as-is from orbit without any additional descent paraphernalia, and it would make it to the ground completely unscathed.