Quadcopters these days very precious. They take off and hover, take pictures or whatever, then land, recharge — and blah. If these drones were birds, they would be prey. But the Nature-Inspired Grasper Aircraft, or SNAG, will be their apex predator. This new quadcopter has foot, each equipped with four 3D-printed nails that lock around anything that comes in contact with them, be it a tree branch to rest on or perhaps, one day, other drones flying in where they are not allowed. That’s right, it’s a drone that can hunt drones.
Over the years, quadcopters have dominated the skies, but the landings aren’t so much: A drone can flip and land its propeller on a moderately uneven surface. Birds, by contrast, can wrap their feet around almost anything, clinging to their toes and claws, which they can afford thanks to the roughness of the branches. “Everything is a landing spot for a bird,” said David Lentink, a biologist and roboticist at the University of Groningen in the Netherlands and co-author of a new work. paper describe the robot in the diary Robotics Science. “For us, this was really inspiring: The whole idea that if you just design different landing gear, you could park it anywhere.”
SNAG is specifically inspired by the peregrine falcon, a predator among predators. This raptor dives and drops bombs at speeds up to 200 miles per hour, slamming into other birds in the air and pressing its claws into their flesh. It is the fastest animal on earth and an absolute threat in the sky.
At 1.5 pounds, the SNAG is actually about the size of one, although it has no wings and significantly more propellers. When one of the SNAG’s legs comes into contact with a tree branch, it begins to collapse, flexing like you would when you bend your knee. The impact lengthens the tendons in the leg, pulling the cord on the underside of each toe. The more the leg bends, the more tension is put on the tendon, until the quick release mechanism activates the spring to pull the tendon tighter, increasing the grip force. Both the claws and toe pads, which are made of deformable rubber coated with duct tape, help the SNAG to hold tight.
Basically, the robot’s legs converted the energy of its impact with the tree branch into grasping energy in just 50 milliseconds. “The robot has Inertia— it doesn’t look like a helipad,” said Lentink. “It was a dynamic landing, a controlled collision.” After landing, an accelerometer on the SNAG’s right leg will check the robot’s balance, and a hip motor will correct its posture if necessary. To release the grip, another motor relieves tendon tension. Because of the elastic band at the tips of the toes, the numerals automatically roll back to the open position when this tension is released, allowing the SNAG to fly away.
In this video you can see the robot’s legs work to capture “prey”, the way a falcon might attack other birds from above. When objects come into contact with the foot, the energy of that impact is converted into energy that the robot uses to grip its claws.
And this is the take-off in slow motion. The SNAG relies on its propellers to generate lift, just as a hummingbird relies on rapid flapping of its wings to take off. (A real peregrine falcon would flap and shove with its powerful legs to get off the ground.)
One of the current limitations of SNAG is that it is not autonomous. To carry out these experiments, a pilot had to control the robot remotely. But Lentink and his colleagues are finding a way for the robot to locate a branch, calculate how to approach it, and land itself.
The SNAG isn’t the first quadcopter with legs. DrOne Caltech’s Aerial Robot (aka Leonardo), due out in 2019, has limbs to rest on the ground; It is designed to better explore Mars. However, both SNAG and Leonardo pursue the same thing: energy efficiency. Making a drone hover in place to track an area quickly drains the battery. (NASA has send a helicopter to Mars, but it has no legs, so its flight time is very short.)
