Big step forward in 3-D robot design
whether they could use 3-D printing to build a material capable of sensing its environment — to measure the surrounding temperature, for instance, and to notice if it was struck or being squished.
Once they met that goal, they added another. “We started to think, in addition to sensing, why not make it move?” Zheng said.
And they still wanted to do it all in a single step.
Ordinary 3-D printers work like a machine that adds icing to a cake. They build up thin layers of plastic, metal, glass or other materials to produce an endless list of products such as jewelry, tools, prosthetics and even pizza. But they can only print one component at a time.
To print an entire robot at once, Zheng and his colleagues needed a versatile material. So they created one out of silicon carbide, which supports the robots’ structure; electrodes made of copper and gold, which carry current; and piezoelectric ceramics, which change shape in response to an electric field.
Each part contributes to a whole new “metamaterial” that can bend and flex, stretch and squeeze, as well as twist and turn, said Huachen Cui, a postdoctoral researcher in Zheng’s lab who spearheaded its development. And the metamaterial can be 3-D printed in one go.
The new material required a custom 3-D printer, so the team built one that takes up the space of an office desk. The way it works is similar to flash-freezing a design in a glass of water and draining away the rest of it, leaving an intricate ice sculpture behind. But instead of water, the printer alternates between vats of the three ingredients, then uses ultraviolet light to solidify each layer of the metamaterial lattice as the robot takes shape.
The result is basically like a muscle. “It has everything integrated from structural components, sensing components, all the way to motion and electronic control,” Zheng said.
In other words, MacCurdy said, it’s a truly functional object: “When it comes out of the 3-D printer, it doesn’t require additional assembly.”
Cui put a robot through its paces by placing it on a table between a pair of pipes. A set of wires tethered the robot to a power source. When the power was switched on, the robot sparked to life with an uncharacteristic bright green flash accompanied by wisps of smoke. But soon it was moving with the soft buzzing hum of an electric shaver.
The three parts of its Nshaped body form a muscle that flexes faster than the eye can discern, propelling it forward with ease. It can even jump over tiny hurdles about 1 millimeter high.
The design was inspired by nature.
“I wanted to make it agile and very fast — the first thing I could think about was a leopard,” said Cui, who was the study’s lead author. “You just need to hit the ground and move forward. That’s it.”
The robots rely on ultrasound to sense their surroundings, like bats. But instead of using echolocation, the machines employ a 3-Dprinted remote sensor that bounces radar pulses in various directions. The way they bounce back alerts the robot to obstacles in its path so it can adjust accordingly.
The machines, which are small enough to fit on a penny, can carry more than 13 times their own weight. When Cui dropped a bolt into a basket affixed to the top of the robot, it jolted and started moving faster. The impact, meant to mimic falling debris, was its cue to make a quick escape, he said.
Zheng said it wouldn’t be hard to make the robots bigger — all they’d need is a bigger 3-D printer. The real challenge is to make the robots smaller, and capable of operating in water.
This is something that excites Sochol.
“I think biomedical applications, particularly drug delivery, is an application where this could really have a legitimate use,” he said. He envisioned a scenario in which a tiny robot carries a dose of medicine to a particular location in a blood vessel. Once it’s in position, doctors could “hit it with an electric field” to get it to release its payload.
Zheng’s lab is already outfitted with a small tank on the floor to test a future generation of aquatic robots. If a leopard inspired the original version, the new ones will be designed to mimic the swimming and crawling abilities of shrimp.