Is that a bird or a drone watching you from the telephone wire? A drone with legs can perch just like a bird – or land and walk on flat surfaces. Bhargav Gajjar of Vishwa Robotics in Brighton, Massachusetts, designed the legs as an add-on for small US air force drones.
Small drones generally lack landing gear. Many rely on a controlled crash-landing, a somewhat crude approach compared with the elegant precision landing of a perching bird. Gajjar studied dozens of bird species and recorded their landings using a high-speed camera. His drone's legs are based on those of the American kestrel.
The drone perches in an upright position with a powerful gripping action from an electric motor. Its claws are extremely sharp so that its grip is difficult to break.
A remote computer uses footage from a camera fitted to the drone to control flight and get the drone into the correct position for landing. Just like a real bird, the drone has to brake sharply just above its landing site and perform a controlled stall in order to touch down. Birds' legs also act as shock absorbers, and the mechanical version mimics this.
Gajjar's perching legs can waddle short distances, so the drone can explore indoor spaces.
Stealthy watcher
A perching drone can occupy any convenient vantage point, making it stealthier and giving a closer view than one circling overhead. Perching uses no power, and a perching drone recharging from solar cells could operate indefinitely. Gajjar has flown his legs on fixed-wing drones, but is using a quadrotor inside the laboratory.
Copying animals in ways like this appeals to Justin Thomas of the University of Pennsylvania's General Robotics, Automation, Sensing and Perception (GRASP) Laboratory. "Such a biomimetic approach would have advantages in extending the working time of an aerial robot by allowing it to perch and save energy," he says. His team has previously created a drone that can grab objects on the ground
"This could be particularly advantageous for applications such as environmental monitoring and establishing temporary communication networks, such as in the case of a natural disaster," Thomas says.
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