  Modular self-reconfigurable robots (MSRRs) offer enhanced task flexibility by
constructing various structures suitable for each task. However, conventional
terrestrial MSRRs equipped with wheels face critical challenges, including
limitations in the size of constructible structures and system robustness due
to elevated wrench loads applied to each module. In this work, we introduce an
Aerial MSRR (A-MSRR) system named BEATLE, capable of merging and separating
in-flight. BEATLE can merge without applying wrench loads to adjacent modules,
thereby expanding the scalability and robustness of conventional terrestrial
MSRRs. In this article, we propose a system configuration for BEATLE, including
mechanical design, a control framework for multi-connected flight, and a motion
planner for reconfiguration motion. The design of a docking mechanism and
housing structure aims to balance the durability of the constructed structure
with ease of separation. Furthermore, the proposed flight control framework
achieves stable multi-connected flight based on contact wrench control.
Moreover, the proposed motion planner based on a finite state machine (FSM)
achieves precise and robust reconfiguration motion. We also introduce the
actual implementation of the prototype and validate the robustness and
scalability of the proposed system design through experiments and simulation
studies.
