A team of researches with members from the U.S., China and Sweden has developed a new kind of foot landing structure for drones to allow them to perch on tree limbs or other elongated objects. After grasping atop the object, the drone can deactivate one or more of its rotors, saving battery power, but the camera aboard can still function allowing the drone to continue its mission, for example, monitoring conditions below. The paper published in the journal Science Robotics describes the new landing gear and details of experiments.  

In most cases quadcopters are used for monitoring and other missions where drones perch at relatively high altitudes that people cannot reach. But flight endurance of modern electrical UAVs usually does not exceed half an hour, whereas IEC-powered hybrid drones carry less payload. As a rule, engineers resolve this problem by increasing capacity of the batteries.

A team of researches headed by Fu Zhang from the University of Hong Kong came up with a way to extend the flight time of a drone by reducing the power consumption of its rotors, being the main power consumers. The researchers used another approach, inspired by birds and other flying animals, because in normal conditions low power consumption causes loss of thrust and can make a drone fall down. They proposed to equip drones with “feet” that allow them to grasp atop tree limbs, edges of building structures and other objects that can be exploited as a force support for deactivating one or more rotors.

Such “feet” require no specifically invented drones and can be mounted on the bottom side of most standard COTS UAVs. The landing gear design consists of a base and three fingers. Different contact modules attached to the fingers (two hook-shaped and two L-shaped contact modules) allow a drone to grasp itself on other structures. The drone can hook on thin objects and turn off its rotors completely. L-shaped contact modules below the center of the drone are required for maintaining the balance, when some of its rotors are turned off. In addition, the drone can grasp around elongated objects, such as tree limbs, turn off all its rotors and turn over.

Landing gear elements and ways of the drone’s stabilization on various objects

Kaiyu Hang et al. / Science Robotics, 2019

The researches demonstrated advantages of their approach, having measured power consumption of the drone in the perching and resting states. When a drone grasps or hooks around structures, it can turn all rotors off. In the rest modes it still consumes some power, but the consumption rate is much less. For instance, when resting on a support structure two rotors can be turned off completely or all motors can remain turned on with their thrust reduced significantly. As demonstrated by the experiments, the land gear design allows to reduce power consumption of a drone in several times as compared to normal hovering in the air. In addition, it makes drones more stable that can be useful in case of filming a video

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In 2016, Japan engineers designed a drone equipped with two robotic arms, but those were used for different tasks. The developers proposed to use such drone to ease grasping and carrying operations in cargo delivery. Each of two arms can carry a maximum payload of 10 kg (22 lbs.) with the total maximum payload of the drone being 20kg (44 lbs.).

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