Design, Control, and Motion Strategy of TRADY: Tilted-Rotor-Equipped Aerial Robot With Autonomous In-flight Assembly and Disassembly Ability

In this airticle, we introduce a novel aerial robot unit called TRADY, which is a tilted rotor-equipped aerial robot with autonomous in-flight assembly and disassembly ability. One TRADY unit can be combined and separated from another TRADY unit in the air autonomously, thereby extending or reducing the degree of control freedom of the aircraft. This robot is controlled by under-actuated model as a quadrotor in the unitary state, and when the two units are assembled, they are controlled by fully actuated model as a single octorotor. This system is achieve by tilted rotors with optimized tilt angles and the docking mechanism capable of both doking and undocking with high precision. Furthermore, we present a novel system configuration that allows to switch controllers between under-actuated and fully-actuated in the air, including the state transition method to compensate for discrete changes during system switchover. In the experiment with the real mahine, TRADY is able to perform aerial assembly and disassembly motion with a success rate of about 90% by using a new motion plan that employed recovery behavior from hazardous conditions. We also confine through task execution experiments that, by assembling two units, TRADY can control transition and rotation independently, and it produces more than 9 times the torque of a single unit moreover. To the best of our knowledge, this work represents the first time that a robot system has been developed that can perform both assembly and disassembly while seamlessly transitioning between fully-actuated and under-actuated models.