Recently we wrote about a drone with wings modeled after dragonfly wings. Now engineers at Draper lab have taken bio-inspired drones a step further, by developing a micro aerial vehicle that combines an actual dragonfly with electronics. They call it DragonflEye.
Draper’s invention fits a living insect with a tiny “saddle” of electronics powered by a photovoltaic cell. The real breakthrough, however, is in directing the bug where to fly.
Dragonflies were selected for the project for many of the same reasons aerodynamicists and others study them: “They’re just very, very amazing flyers,” says Jesse Wheeler, a biomedical engineer leading the project at Draper. According to Wheeler, a dragonfly can hover, negotiate winds up to 30 mph, and tolerate accelerations up to 9-Gs. “And they can carry quite a bit of weight for their little size.” A typical dragonfly weighs anywhere from 600 milligrams to 1 gram. The saddle adds 200 milligrams (about as much as a dried maple leaf), or up to a third of the insect’s own weight.
Dragonflies have been around for 350 million years, but neurologically they have remained quite simple. The Draper project takes advantage of that simplicity by stimulating only 16 nerve cells of the thousands in the insect’s spinal cord. These 16 cells are known as “steering neurons” because they control the dragonfly’s direction of flight. While Wheeler believes other insects have similar neurons, they haven’t been identified. “That’s another reason the dragonfly was interesting to us.”
He and his team guide DragonflEye with pulses of light, which requires that they first genetically modify the steering neurons with a protein known as an opsin. Naturally found in the eyes of most light-sensing creatures, opsins can be selected for sensitivity to specific colors. The opsin stimulates its steering neuron when light pulses of a particular color are shot into the dragonfly’s nerve cord.
“This nerve cord we’re trying to stimulate is only about 300 micrometers in diameter. So it’s like the size of a thick hair,” says Wheeler. Because the nerve cord is so small, “typical optical fibers just aren’t going to cut it.” So Draper developed a new material they call Draper Waveguide. This new material is smaller and much more flexible than glass-based fiber optics, and it doesn’t leak light.
Nerve stimulation by light has a big advantage over electrical stimulation using implanted electrodes. “If you were to put in an electrode, and drive even the tiniest amount of current,” says Wheeler, “you’re gonna activate lots of different neurons. And that’s not beneficial because you’re activating everybody.” Light-based stimulation can be much more selective.
Because DragonflEye is an internal Draper project, it isn’t driven by commercial or military requirements. But its organic nature and tiny size means it would be highly stealthy to radar and difficult to detect. Among its possible aerial missions, says Wheeler, are temperature monitoring and chemical detection. Video surveillance and other sensors are also on the horizon. “Right now,” says Wheeler, “we’re just focusing on getting the navigation data out. We’re not focused on pulling out any other sensor data.”