Solar-Powered RoboBee X-Wing Flies Untethered

Just this week, in this very galaxy, X-Wing achieves liftoff

Solar-Powered RoboBee X-Wing Flies Untethered
Photo: Harvard Microrobotics Lab
The new RoboBee X-Wing features solar cells, an extra pair of wings, and improved actuators, and it can fly untethered for brief periods of time.
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The first generation of robotic bees were designed to be very bee-like, featuring two flapping wings at bee scale. After all, bees can do a lot with two wings, so why can’t robots? Turns out there are a lot of reasons why little winged robots can’t do what bees do, at least for now—things like yaw control has proved to be somewhat tricky, which is one reason why less explicitly bee-like designs that use four wings instead of two are appealing

We saw some impressive research at ICRA this year showing that yaw control with two wings is possible, but four wings have additional advantages— namely, more wings means more power for lifting more stuff. And with more lifting power, it’s possible to have a completely self-contained robot insect, even if it’s slightly weird looking.

In Nature this week, researchers from Harvard’s Microrobotics Lab, led by Professor Robert J. Wood, are presenting a four-winged version of their RoboBee platform. They are calling this version RoboBee X-Wing, and it’s capable of untethered flight thanks to solar cells and a light source that would put high noon(s) on Tatooine to shame.

We should point out that this is not the first light-powered self-contained winged robot insect that we’ve seen take flight. Last year at ICRA, a group from the University of Washington demonstrated a two-winged robot that could take off when a laser was directed at its solar cell. The Harvard researchers say that the flight of their robot is “sustained” rather than just a “liftoff,” which is open to interpretation to some extent, but there’s plenty of room for exciting innovation in this space, so being the “first” to do whatever is (in my opinion) less important than just making it work in the first place.

Anyway, RoboBee X-Wing is 5 centimeters long and weighs 259 milligrams. At the top are solar cells, and at the bottom are all of the drive electronics you need to boost the trickle of voltage coming out of the solar panels up to the 200 volts that are required to drive the actuators that cause the wings to flap at 200 Hz. The reason the robot’s bits and pieces are arranged the way that they are is to keep the solar panels out of the airflow of the wings, while simultaneously keeping the overall center of mass of the robot where the wings are. The robot doesn’t have any autonomous control, but it’s stable enough for very short open loop flights lasting less than a second.

The reason for the solar cells is that the robot can’t lift the kind of battery that it would need to power its wings, so off-board power is necessary. And if you don’t want a tether (and seriously, who wants a tether!) that means some kind of wireless power. UW used a laser, but X-Wing makes due with the sun. Sort of. Three suns, actually, since one isn’t enough, and the researchers emulate that with some powerful lamps. This means that X-Wing isn’t yet practical for outdoor operation, although they say that a 25 percent larger version (that they’re working on next) should reduce the number of suns required to just 1.5, which means that maybe it would work on, like, Venus, or something.

In its current version, RoboBee X-Wing does have some mass budget left over for things like sensors, but it sounds like the researchers are primarily focused on getting that power requirement down to one sun or below. It’s going to take some design optimization and additional integration work before RoboBee X-Wing gets to the point where it’s flying truly autonomously, but what we’ve seen here is a substantial amount of progress towards that goal. 

“Untethered Flight of an Insect-Sized Flapping-Wing Microscale Aerial Vehicle,” by Noah T. Jafferis, E. Farrell Helbling, Michael Karpelson, and Robert J. Wood from Harvard University, appears in the current issue of Nature.

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