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At a Glance
Researchers at Colorado State University have developed a compliant bistable gripper designed to enable perching and grasping capabilities in aerial robots. Introduction of the feature affords aerial quadcoptors the ability to perch on trees, powerlines, and the like, enabling these devices the invaluable feature to rest and recharge while maintaining desired heights for monitoring (without flying).
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Aerial robots with multiple rotors (e.g., quadcopters) are widely used in various civilian and military situations. However, multi-rotor based aerial robots face a critical bottleneck: limited flight time. In fact, the flight time for commercial quadcopters is usually less than one hour due to the low aerodynamic efficiency and high energy consumption. One possible solution is to allow aerial robots to land or perch on an object (e.g., trees, power lines, or roof) so that they can save and even harvest energy instead of hovering in the air; meanwhile, they can still monitor or surveil an interested area. However, successful perching for aerial robots is challenging since it involves several important parts including mechanical perching mechanism design, flight state estimation, motion planning and control.
The compliant bistable gripper mechanism is made up of four main parts: (1) three fingers (upper and lower), (2) three soft silicone tubes, (3) a base with three vertical beams, and (4) a contact pad. A bistable mechanism was employed as the gripping mechanism needed the ability to remain at two stable states without power input. This key feature of bi-stability allows the mechanism to change from one state to another with an activation force – specifically contact velocity.
Uniquely, the bistable mechanism for perching and grasping is constructed of a lightweight 3D-printed Polylactic acid (PLA) material and commercially available silicone tubes for compliant joints. Such a design allows for rapid and economic exploration of different size and characteristics of variations in mechanism. The mathematical models established for the bistable mechanism characterize the activation forces necessary for proper operation. These models also formulate basic design guidelines to achieve desired activation forces based on expanded requirements from perching and grasping.
Figure 1 (Left) Perching system. The bistable gripper is installed on the Crazyflie with open state. The Crazyflie can close the gripper and perch on horizontally hanged object. The motor driver and resistance wire are used to release Crazyflie from perching
- Easy to close: activation force is small enough for small aerial robots to exert
- Stable to hold: activation force at closed state is (1) large enough to hold the weight of an aerial robot during perching, and (2) strong enough to grasp the weight of various payloads
- Easy to adjust: the gripper is easily adjusted for both differing sizes of aerial robots and payload weights
- Light weight and economical: made of 3D-printed material
- Energy efficient: perching allows for rest and recharging of aerial robots
- Versatile installation: Can be installed above or below the aerial robot depending on application
- Civilian and Military applications
- Search and Rescue