A transformable tethered aerial platform for robot-environment interactions

Improving the adaptability and versatility of micro aerial robots is crucial for expanding their application range. In this paper, we present a transformable tethered aerial platform composed of two bicopters tethered together with a cable, which is capable of mid-air transitions and robot-environment physical interactions. The platform can operate in three modes: free-flight mode, tethered-flight mode, and quadcopter mode. These modes are enabled by changing the tension and length of the cable, without the need for additional reconfiguration mechanisms. To fully exploit the capabilities of the proposed system, we derive the dynamic model of the platform and develop the control methods for each mode. The developed controller ensures stable flight in each mode and also enables the platform to operate with limited position feedback. We validate the feasibility of the transformable design through a series of experiments, demonstrating stable transitions between modes and effective physical interactions. Notably, by using the cable as an end effector, the platform can exert forces and torques on the environment through cable tension, eliminating the need for extra grippers or actuators and showcasing the versatility of the system in real-world tasks.