The Defense Department is pursuing the development of bird-like and insect-sized flying robots to give troops more overhead surveillance options in future conflicts. By 2015, the Air Force intends to field an avian robot that can operate semi-autonomously for a week to detect harmful chemicals and explosives. It will have a two-foot wingspan and the ability to perch to collect video data and recharge onboard batteries.
Scientists have figured out how to make small aircraft fly and even hover by using flapping wings. But enabling those drones and their fixed-wing counterparts to alight safely on rooftops and phone wires remains one of the toughest technical hurdles.
"The important part is the landing gear," said Bhargav Gajjar, president of Vishwa Robotics and Automation LLC, a firm based in Brighton, Mass. Under a contract with the Air Force Research Laboratory, he has developed bird-like feet and claws to do the job.
Drawing inspiration from Leonardo da Vinci's study of birds and flight, Gajjar investigated the muscles and tendons in avian feet.
"It's all about muscles," he said. "How do birds' muscles grab this quickly? How do they stay perched? "
Gajjar began copying the structures into robotic mechanisms composed of gears, springs and levers that could operate without electrical motors.
"The entire idea is to use mechanical systems instead of electrical systems to perch, but use electrical systems to unperch and walk around," he said.
Mimicking how birds land has proven difficult.
"Ever seen a bird perch? They do these high-stall maneuvers, where they lift their heads up with their wings out, and they gently perch," Gajjar said.
"It's easy to perch when you fly very slowly," he pointed out. The trick is landing when the robotic bird swoops in at high speeds.
"The control involved is very non-linear and it's very fast, even too fast for a small microprocessor," so the only option is to crash land the robot, he said. Gajjar tackled the challenge of making lightweight landing gear strong enough to withstand the crash and also allow the vehicle to "stick."
Over a period of six to eight months, he built 20 different foot-and-claw prototypes, many as long as the palm of' the human hand. He incorporated everything from small hooks to sticky pads that would allow a bird-sized air vehicle to decelerate and stop in a given area.
"If you use hooks, you cannot grab onto circular objects very well. …