Engines powered by ions are currently carrying satellites outsides of our solar system, but here on Earth, this futuristic propulsion could power miniature robots.
Daniel Drew, an engineering student at the University of California, Berkeley, found himself inspired to study miniature robots from the science fiction he devoured as a child.
Miniature robots inspired by insects could someday be used to search confined spaces for survivors after a disaster, monitor air quality and even fill in as pollinators for real-life insects that have been wiped out of an area.
"Imagine a world where we could tap into the sensory input of every single insect on Earth," Drew said. "That's the kind of high-resolution data we can get."
But as well as these bioinspired prototypes seemed likely to work, Drew said, they ran into a problem that their real-life inspirations didn't face—energy. Unlike an insect, a miniature robot needs a source of power, and that usually means a battery of some kind. But batteries can only get so small, and putting a larger, more powerful battery on a microrobot means the entire robot needs to get larger, defeating the purpose.
Drew said his adviser, however, thought a vintage solution might solve this modern dilemma—ion thrusters. Dating back to the experiments of rocket pioneer Robert Goddard, these engines exploit the simple electrostatic effect familiar to most people who’ve pulled socks stuck together out of the dryer. In essence, ion propulsion works by shooting an electron into a chamber filled with a gas of some kind. When it hits an atom of the gas, that electron knocks an electron off the atom, making it positively charged. A negatively charged grid near the end of the chamber then draws that atom out of the thruster. The force of that atom flying out the thruster propels its craft forward.
That force is as small as an atom, however, and ion thrusters pale compared to the power of fuel or battery powered engines. Attempts to scale up ion thrusters to make them like the engines in Star Wars or even work with hoverboards have been unsuccessful because of how weak the force is. Ion engines have been relegated to the vacuum of space, where satellites using them face no resistance from air and efficiency matters more than speed.
But Drew realized that for all their faults on the macroscale, ion thrusters could work wonders on the microscale.
He designed small-scale versions of ion thrusters, and began working to integrate them into miniature robots. These "ionocraft" are roughly half an inch square, and fly via a tether. Future versions might use tiny on-board batteries to get up to 10 minutes of flight, and Drew hopes to see them become even more efficient. He demonstrated one of his robots at a conference last month in Montreal, Canada. Currently, the craft can’t be steered, but Drew and his team are able to control its altitude, making it akin to a basic quadcopter with its four engines, he says. With its lack of moving parts and silent propulsion, Drew says that onlookers have described the ionocraft as “spooky” and “like a UFO.”
Drew is now working to improve the thrust on his microrobots to make them move faster and more powerfully, as well as thinking about how these ionocraft will be steered one day and even how humans will interact with them psychologically as these devices start to enter everyday life. He envisions VR simulations that would pair humans with a swarm of these microrobots that one could encounter.
"Microrobotics is such a young field," Drew said. "You have to push on every aspect of it to make progress."
An earlier version of this article incorrectly stated that the ionocraft fly via battery. Currently, the craft are tethered to a power source, but future versions may use battery power. Smithsonian.com regrets the error.