Scientists Showcase a Solid-State Ornithopter Design — But Lack the Materials to Build It
Bird-like flapping-wing robots with no motors or gears have been proven in simulation, but materials science needs time to catch up.
Scientists have made a big step towards building solid-state robots that fly like birds, without needing any motors, gears, or mechanical linkages — now they just need to discover the materials that will bring their simulations to life.
"Things that need to move fast must be lightweight. That's why bird wings are delicate structures, and aircraft wings mimic bird wings," explains co-author Onur Bilgen of the thinking behind the team's work into solid-state bird-like robots. "We don't want to just mimic nature. We want to exceed what nature does. We want to achieve flapping flight without bone-like structures or muscle-like actuators, flapping in a much simpler way."
Most flying robots today use propellers, either in a quadcopter-like formation or to drive a more traditional fixed-wing aircraft body. In an ornithopter, lift and propulsion are handled through bird- and insect-like flapping wings — but they are still powered by a motor. In a solid-state version, though, there are no motors at all, just materials that act like a bird's muscles — in the case of the researchers' work, macro-fiber composites (MFCs) which curl and twist in response to the flow of electricity.
"We apply electricity to the piezoelectric materials, and they move the surface directly, without extra joints, extra linkages or motors," Bilgen explains. "The wing is a composite including a piezoelectric material layer and a carbon-fiber layer. Apply voltage to the piezoelectric layer, and the whole composite flexes. The carbon fiber acts like feathers and bone, and the surface-mounted MFCs act like muscles and nerves."
There's only one problem: while the team has proven the concept in simulation, no presently-known material can handle the task. "Today's piezoelectric materials are not capable enough," Bilgen admits. "However, our mathematical model allows us to look into the future with reasonable assumptions. We've scientifically demonstrated that this type of ornithopter can be possible when we make certain material assumptions. We can show the feasibility of designs that are not yet physically possible."
The team's work has been published in the journal Aerospace Science and Technology under closed-access terms.