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US Army and University of Maryland create realistic robotic bird

04 June 2013

A robotic bird created by US Army and University of Maryland researchers is tricking real flocks in middair, making it a potential clandestine military tool.

Robo-Raven in flight
Robo-Raven in flight

Robo-Raven glides, soars and flaps like a real bird. Complete individual wing control allows for extreme aerobatics that no other mechanical bird has ever been able to perform, US Army Research Laboratory (ARL) researchers claim. But its ability to hide in plain sight and its light weight is what excites the researchers most.

"It already attracts attention from birds in the area which tends to hide its presence," said John Gerdes, a mechanical engineer with the Vehicle Technology Directorate at the Aberdeen Proving Ground in Maryland.

Seagulls, songbirds and sometimes crows tend to try to fly in a formation near the bird during testing, but birds of prey, like falcons and hawks take a much more aggressive approach toward test flights.

"Generally we don't see them coming," Gerdes said. "They will dive and attack by hitting the bird from above with their talons, then they typically fly away."

With the aggressive manoeuvres they are working on, the perch and stare mission could be possible, and when combined with solar cell wings that the University of Maryland is working on, researchers could land and charge the Robo-Raven then resume a mission.

Robo-Raven is much quieter than the helicopter or propeller, so it could get much closer to an adversary without revealing its presence. It's made out of carbon fibre, 3D-printed lightweight thermal resistant plastic, Mylar foil and foam. The geometrically complex figure is shorter than two feet and weighs less than a can of fizzy drink.

Programmed wing motion helps Robo-Raven's wings maintain optimal velocity during the flap cycle to achieve the right balance at takeoff.

Gerdes began building Robo-Raven in 2008 as part of graduate research at the University of Maryland's Advanced Manufacturing Laboratory that focused on developing a tech demonstrator for manufacturing techniques that morphed into a variety of spinoff research efforts.

Dr S K Gupta, a professor in mechanical engineering, began working on flapping-wing robotic birds nearly a decade ago. According to a University of Maryland news release, Gupta and his graduate students, along with mechanical engineering professor Hugh Bruck, first successfully demonstrated a flapping-wing bird in 2007. This bird used one motor to flap both wings together in simple motions.

By 2010, the design had evolved to more than four successive models. The final bird was able to carry a tiny video camera, could be launched from a ground robot that ARL researchers created called the Lynchbot, and could fly in winds up to 10mph - important breakthroughs for robotic micro-air vehicles that one day could be used for reconnaissance and surveillance.

Inside ARL laboratories, Gerdes tested motors to determine the power curves using a micro dynamometer. He also worked to model the aerodynamic forces generated during flapping. The wings are based on a design he created for his master's thesis project, but have been scaled up to match the more powerful motors the team is currently using.

The robot uses a fly-by-wire approach, so a handheld radio is used to control the flight.

"We were inspired by the capabilities of the bird much more than the anatomy of the bird," Gerdes said. "Our approach was more bio-inspired than bio-mimetic. In some ways this simplifies the design because we can focus on functional aspects without necessarily adopting the same set of constraints that apply to animals."

Gerdes said many of the design features that animals have evolved are a fantastic starting point, which can be seen in their design.

"For example, we use hollow stiffeners to provide a stiff and light-weight structure, and our wing spars have been arranged in a fan pattern to create the desired airfoil shape during the flapping motions," Gerdes said. "At any time, we can transition between these behaviours with total control over the wings."

The way they do this is to separately drive each wing with its own actuator, removing any coupling between the two wings, which has been the traditional approach to 'ornithopter' (robotic bird) design.

"A major challenge in realizing this approach was overcoming the strict weight limitations," Gerdes said.

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