Unmanned Systems Technology 025 | iXblue DriX I Maintenance I UGVs I IDEX 2019 I Planck Aero Shearwater I Sky Power hybrid system I Delph Dynamics RH4 I GCSs I StreetDrone Twizy I Oceanology Americas 2019

10 Platform one April/May 2019 | Unmanned Systems Technology Researchers at Yale University are looking at using perching to help small UAVs extend their mission time by saving battery power (writes Nick Flaherty). Most strategies for UAV perching require complex manoeuvring for landing and specific structures to land on, such as rough walls for latching on to or tree branches for grasping. This can take more time to achieve and so use up more battery power. The researchers are therefore looking at an approach called ‘resting’. This uses a modular design for landing gear that allows the UAV to perch and rest on a range of structures. The approach allows rapid prototyping with additive manufacturing to produce different claws for perching on various structures. Actuators allow switching between different modes of perching and resting during flight, and enable perching by grasping, allowing a UAV with a large payload to rest on structures such as street lights or the edges or corners of buildings and so extend its mission time. The landing gear consists of an actuated gripper module and a set of contact modules that are mounted on the gripper’s fingers. The gripper is mounted on the underside of the UAV and, for its weight and size, is compliant with a wide range of off-the-shelf UAVs. If a horizontal surface is available, the gripper is opened and its fingers are used as landing skids, similar to a bird landing on a flat roof. If a cylindrical structure is available, the UAV approaches it from above such that the gripper can grasp the structure, then all motors can be switched off to save power. For other types of structures such as the edges or corners of a building, struts or street signs, modular contact modules can be matched to the specific structure, with corresponding control software for the structure. The team added the landing gear to a DJI F450 quadcopter and tested it in different scenarios, from rods that replicate branches to the edges of buildings. The carbon fibre base and gripper fingers were 3D-printed using TangoBlackPlus to minimise weight, and the environment was perceived using an external Kinect One sensor, which provided point clouds to detect structures that would allow perching and resting. Once the contact locations are identified, the UAV can be autonomously navigated on the basis of localisation provided by a Vicon system. The gripper module consists of servomotors, a set of three fingers and a base platform attached to the bottom of the UAV. To ensure sufficient grasping forces, three servomotors are used to actuate the fingers separately, but all the fingers can be actuated by a single motor as long as the torque provided is sufficient for the grasping. When the gripper is opened, the fingers enable normal landing and take-off from the ground, because the fingertips are in a level position under the UAV. Airborne vehicles Perching power-saver Outline design of a UAV’s landing gear to allow perching and resting (Courtesy of Kaiyu Hang) The landing gear consists of an actuated gripper module and a set of contact modules that are mounted on the gripper’s fingers