It was a late afternoon in August when Elizabeth Farrel Helbling, PhD '19 and Noah T. Jafferis saw a major breakthrough in their Harvard Microbotics Lab.
Helbling is a graduate student and Jafferis her postdoctoral fellow from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), the Graduate School of Arts and Sciences and The Wyss Institute for Biologically Inspired Engineering.
Six years of sweat, blood, and tears finally paid off, and they even caught the ground-breaking moment on camera.
Helbling counted down. “Three, two, one, go,” and up went the Robobee on its very first solo flight. The bright halogens turned, and the solar-powered mechanical bee lifted into the air.
At first, he flew straight for the lights as he had no on-board steering and control, but Helbling caught the tiny robot just in time by cutting the power. Thankfully, the Robobee’s Kevlar safety harness kept it from falling.
In the short clip you hear Helbling laugh nervously and note, "That went really close to me."
Jafferis excitedly responds, "It went up!"
The feat of these two scientists is revolutionary. The Robobee is the lightest vehicle to ever achieve untethered flight! It took 6 years of work and an additional pair of wings, but it finally worked.
"The change from two to four wings, along with less visible changes to the actuator and transmission ratio, made the vehicle more efficient, gave it more lift, and allowed us to put everything we need on-board without using more power," said Jafferis.
Some have begun to call Robobee X-Wing instead, like the four-winged starfighters from Star Wars.
"This is a result several decades in the making," said Robert Wood, Charles River Professor of Engineering and Applied Sciences at SEAS, Core Faculty member of the Wyss Institute and principle investigator of the Robobee project.
Powering flight is something of a Catch-22 as the tradeoff between mass and power becomes extremely problematic at small scales where flight is inherently inefficient.
It doesn't help that even the smallest commercially available batteries weigh much more than the robot. We have developed strategies to address this challenge by increasing vehicle efficiency, creating extremely lightweight power circuits, and integrating high efficiency solar cells."
It was the addition of the second pair of wings that allowed Helbling and Jafferis to finally cut the power cord and untether the Robobee, attaching solar cells – the smallest commercially available weighing 10 milligrams each with .76 milliwatts per milligram of power when the sun is at its fullest intensity – and an electronic panel which resides underneath the belly about 3 centimeters above the wings instead.
In order to fly, Robobee needs the power of about 3 earth suns which means outdoor flight is not a possibility yet. For now, the two researchers simulate the necessary level of sunlight within the lab.
These solar cells are attached underneath the bee to an electronics panel, converting low voltage signals into high voltage drive signals in order to control the actuators.
The robotic bee weights 259 milligrams altogether and uses less power than one single bulb on a string of LED Christmas lights – 120 milliwatts of power, to be exact.
"When you see engineering in movies, if something doesn't work, people hack at it once or twice and suddenly it works. Real science isn't like that," said Helbling. "We hacked at this problem in every which way to finally achieve what we did. In the end, it's pretty thrilling."
"Over the life of this project we have sequentially developed solutions to challenging problems, like how to build complex devices at millimeter scales, how to create high-performance millimeter-scale artificial muscles, bioinspired designs, and novel sensors, and flight control strategies," said Wood.
"Now that power solutions are emerging, the next step is onboard control. Beyond these robots, we are excited that these underlying technologies are finding applications in other areas such as minimally-invasive surgical devices, wearable sensors, assistive robots, and haptic communication devices -- to name just a few."
The researchers will continue to develop and transform the Robobee, and Harvard is looking for ways to commercialize the results. What they’ve accomplished so far, however, is described in more detail in Nature.
National Science Foundation and the Office of Naval Research supported this research, and it was co-authored by Michael Karpelson.