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

TL;DR

This work tackles the mobility/manipulation trade-off in aerial robotics by introducing TRADY, a Tilted-Rotor-Equipped Aerial Robot that can autonomously assemble/disassemble in flight and switch between under-actuated and fully-actuated control using $n=4$ units in the single state and $n=8$ in the assembly state. It combines a high-rigidity docking mechanism (magnetic switch plus movable pegs), an optimized rotor configuration, and a dual-model control framework with transition processing to maintain stability during model-switch events, supported by thrust-allocation strategies for both states and a convex-polyhedron-based optimization of rotor directions. A motion-strategy built on a finite-state-machine ensures safe, autonomous assembly/disassembly in mid-air, including recovery behavior for hazardous conditions. Experimental results demonstrate a $86.7\\%$ assembly reliability, $100\%$ disassembly reliability, and up to a ninefold increase in torque in the assembly state, validating TRADY’s ability to perform integrated assembly/disassembly with seamless model switching and practical manipulation tasks such as peg insertion and valve operation.

Abstract

In previous research, various types of aerial robots were developed to improve maneuverability or manipulation abilities. However, there was a challenge in achieving both mobility and manipulation capabilities simultaneously. This is because aerial robots with high mobility lack the necessary rotors to perform manipulation tasks, while those with manipulation ability are too large to achieve high mobility. To address this issue, a new aerial robot called TRADY was introduced in this article. TRADY is a tilted-rotor-equipped aerial robot that can autonomously assemble and disassemble in-flight, allowing for a switch in control model between under-actuated and fully-actuated models. The system features a novel docking mechanism and optimized rotor configuration, as well as a control system that can transition between under-actuated and fully-actuated modes and compensate for discrete changes. Additionally, a new motion strategy for assembly/disassembly motion that includes recovery behavior from hazardous conditions was introduced. Experimental results showed that TRADY can successfully execute aerial assembly/disassembly motions with a 90% success rate and generate more than nine times the torque of a single unit in the assembly state. This is the first robot system capable of performing both assembly and disassembly while seamlessly transitioning between fully-actuated and under-actuated models.

Figures (21)

• Figure 1: The proposed robot platform TRADY: Tilted-Rotor-Equipped Aerial Robot With Autonomous In-flight Assembly and Disassembly AbilitY. (A)The unitary state and the assembly state of TRADY. (B)Task execution capability of TRADY.
• Figure 2: Application example that can be realized with TRADY developed in this work: Valve opening and closing tasks in narrow and complex spaces.
• Figure 3: TRADY's entire design. (A)Female unit. (B)Male unit. (C)Assembled state.
• Figure 4: How the female mechanism works. In (A), since the magnetic force lines of force extend beyond the system, magnetic forces acts on the outside. In (B), magnetic force does not act on the outsinde because the magnetic lines of force circulate within the system. Note that the size of the switchable magnet is exaggerated in the depiction.
• Figure 5: How the male mechanism works. The pegs are driven by the slider-crank mechanism and inserted into female mechanism.