It’s the ultimate DIY robot, a machine that assembles itself out of a single sheet and then rolls away — all without need for an onboard motor or even wheels.
The so-called rollbot, described this week in the journal Science Robotics, demonstrates the power of origami-inspired automatons. One day, these robots could serve as environmental sensors, interplanetary explorers or as medical devices in the body.
As robots have become increasingly ubiquitous, scientists and engineers have been developing ways to make them softer — allowing them to interface with squishy humans without hurting them, or to react to unpredictable environments without breaking. But strength and durability have traditionally come from metal limbs and mechanical gears, and it’s hard to get the same performance with squishy parts.
Soft and functional robots certainly exist, but many of them come with a few drawbacks. For one thing, they usually have to carry their power source, which means having more hard parts on board.
“You’ll see highly functional soft robots that for example can crawl, can jump, but normally they’re not fully soft,” said study co-leader Arda Kotikian, a materials science graduate student at Harvard University. “And if they are, they’re usually tethered to their power source. You can think of this tether essentially like a leash — so you need your very bulky power supply to be following your robot at all times.”
Origami robots have provided a potential solution to these problems. Inspired by the Japanese art of paper-folding, scientists have begun to carefully print, cut and fold sheets of material that can exhibit remarkable qualities or even perform small tasks.
Although they’re not exactly squishy, these origami bots also count as soft robots because they are flexible, yet they remain strong thanks to the flat, rigid planes between each fold.
“We kind of get the best of both worlds, in that sense,” Kotikian said.
To make a robot that could change shape and move without needing to be tied to a power source, the scientists 3D-printed sheets made of several different materials.
The flat, unbending parts were made of a passive polymer while the folds, or hinges, were made with liquid crystal elastomer, which can dramatically expand and contract when exposed to the right temperature. The thicker they made these elastomer-filled folds, the more torque the hinges produced.
The researchers used two different elastomers, each of which reacted at different temperatures, so that they could control the sequence in which the origami bots folded and unfolded.
They created several moving shapes, including a twisty square and a triangulated polyhedron. But their coup de grace was the rollbot.
When placed on a plate heated to about 200 degrees Celsius, the flat sheet measuring about 4 by 8 centimeters would curl itself into a pentagon, pop out its flaps and slowly roll across the platform — no battery pack required.
The invention was made possible by the shrinking divide between material and machine, said Caltech mechanical engineer Chiara Daraio, a co-senior author of the study.
Traditionally, engineers build a device out of a set of materials and then program it. Here, she said, the materials themselves are programmed — by modifying them, combining them into novel composites and arranging them in complex patterns and shapes.
“The project really started as [a way to] challenge the fundamental limit of materials,” Daraio said.
The rollbot won’t be winning at wind sprints anytime soon. But Kotikian said they may be able to speed up the robot’s motions if they can make its hinges heat up and cool down faster.
Such a device could be designed to respond to a variety of different stimuli — not just temperature but light, electricity, humidity or even differences in acidity, for example.
These robots could serve as environmental sensors or even, if miniaturized, be used in the body to perform such tasks as monitoring and maintaining a healthy gut, Daraio said. They might also be deployed as exploratory robots, Kotikian added.
Tim White, a materials scientist at the University of Colorado at Boulder who was not involved in the work, praised rollbot and its siblings. In the future, he said, such robots could become capable of adapting their responses to changing environmental conditions.
“The next step in robotics is embedding autonomy,” White said.