Harvard’s George Whitesides and Alex Nemiroski, a former postdoctoral fellow in Whitesides’ Harvard lab, have created a type of semi-soft robot capable of standing and walking. The team also created a robotic water strider capable of pushing itself along the liquid surface. The robots are described in a recently published paper in the journal Soft Robotics.
Unlike earlier generations of soft robots, which could stand and awkwardly walk by inflating air chambers in their bodies, the new robots are designed to be far nimbler. Though real-world applications are still far off, the researchers hope the robots eventually could be used in search operations following natural disasters or in conflict zones.
Inspired by arthropod insects and spiders, scientists George Whitesides and Alex Nemiroski have created a type of semi-soft robot capable of walking, using simple materials such as drinking straws and inflatable tubing.
“If you look around the world, there are a lot of things, like spiders and insects, that are very agile,” said Whitesides, the Woodford L. and Ann A. Flowers University Professor at Harvard. “They can move rapidly, climb on various items, and are able to do things that large, hard robots can’t do because of their weight and form factor. They are among the most versatile organisms on the planet. The question was, how can we build something like that?”
The answer, Nemiroski said, came in the form of your average drinking straw.
“This all started with an observation that George made, that polypropylene tubes have an excellent strength-to-weight ratio. That opened the door to creating something that has more structural support than purely soft robots have,” he said. “That was the building block, and then we took inspiration from arthropods to figure out how to make a joint and how to use the tubes as an exoskeleton. From there it was a question of how far can your imagination go? Once you have a Lego brick, what kind of castle can you build with it?”
What they built, he said, is a surprisingly simple joint.
Whitesides and Nemiroski began by cutting a notch in the straws, allowing them to bend. The scientists then inserted short lengths of tubing which, when inflated, would force the joints to extend. A rubber tendon attached on either side would then cause the joint to retract when the tubing deflated.
Armed with that simple concept, the team built a one-legged robot capable of crawling, and moved up in complexity as they added a second and then a third leg, allowing the robot to stand on its own.
“With every new level of systems complexity, we would have to go back to the original joint and make modifications to make it capable of exerting more force or to be able to support the weight of larger robots,” Nemiroski said. “Eventually, when we graduated to six- or eight-legged arthrobots, making them walk became a challenge from a programming perspective. For example, we looked at the way ants and spiders sequence the motion of their limbs and then tried to figure out whether aspects of these motions were applicable to what we were doing or whether we’d need to develop our own type of walking tailored to these specific types of joints.”
While Nemiroski and colleagues were able to control simple robots by hand, using syringes, they turned to computers to control the sequencing of their limbs as the designs increased in complexity.
“We put together a microcontroller run by Arduino that uses valves and a central compressor,” he said. “That allowed us the freedom to evolve their gait rapidly.”
Though Nemiroski and colleagues were able to replicate ants’ distinctive “triangle” gait using their six-legged robot, duplicating a spider-like gait proved far trickier.