In March, the Harvard University researchers behind the RoboBee project wrote an article in Scientific American that detailed the challenges of building a swarm of bee-sized robots. The effort breaks into three loose categories: first, you have to figure out how to build a insect-sized robot that can fly (and build a lot of them—no fancy custom jobs when you’re trying to crank out robots by the thousands). In addition, you have to give these robots enough intelligence to get them to do what you want them to do—to “see” their environment and respond to it appropriately. And third, you have to get them to work as a colony, to coordinate thousands of individuals as they work together towards a shared goal, dividing work even when there’s no centralized authority.
Today, the team checks off one important box: as they report in the journal Science, they have managed to build a RoboBee that can hover:
As the authors describe in Scientific American, the flight mechanics of a coin-sized robot isn’t at all like any other kind of robot flight:
The most obvious challenge in creating a small flying robot is figuring out a way to get it to fly. Unfortunately, the steady progress that has been made in miniaturizing robots over the past decade is of little help to us because the small size of the RoboBee changes the nature of the forces at play. Surface forces such as friction begin to dominate over volume-related forces such as gravity and inertia. This scaling problem rules out most of the mechanical engineer’s standard tool kit, including rotary bearings and gears and electromagnetic motors—components ubiquitous in larger robots but too inefficient for a RoboBee.
The researchers solve the problem by relying on so-called artificial muscles...
...piezoelectric materials that contract when a voltage is applied. The wings can move in two ways—stroking back and forth and rotating their pitch. Instead of the up-and-down motion characteristic of bird flight, think of how you would tread water in a pool with your arms. Muscles control the flapping, but rotation is passive—determined by wing inertia, the interaction of the wing with the air, and the elasticity of the wing hinge.
As you’ll notice in the video, the RoboBee has a small wire hanging down from its underside. The wire is necessary because a robot with a mass of just half a gram doesn’t have much room to carry its own power source. As the researchers admit,
To overcome the demanding energy requirements of flight at small scales, much of the bee’s mass must be taken up by the main actuator and power unit (think “battery,” although we are also exploring the possibility of using a solid-oxide micro fuel cell). The power question also proves to be something of a catch-22: a large power unit stores more energy but demands a larger propulsion system to handle the increased weight, which in turn requires an even bigger power source.
So while we’re not yet at the point where we might expect to see a swarm of thousands of bees take flight, the researchers estimate that within a decade or two, your might imagine the following:
Consider a rescue worker with a box full of 1,000 RoboBees—a package that would weigh less than a kilogram. The RoboBees could be released at the site of a natural disaster to search for the heat, sound or exhaled carbon dioxide signature of survivors. If only three of the robots accomplish their task while the others fail, this is a success for the swarm. The same cannot be said about the current generation of $100,000 rescue robots.
Image and videos courtesy Kevin Ma and Pakpong Chirarattananon, Harvard University