Modular Aerial Robotic Systems (MARS) consist of multiple drone units assembled into a single, integrated rigid flying platform. With inherent redundancy, MARS can self-reconfigure into different configurations to mitigate rotor or unit failures and maintain stable flight. However, existing works on MARS self-reconfiguration often overlook the practical controllability of intermediate structures formed during the reassembly process, which limits their applicability. In this paper, we address this gap by considering the control-constrained dynamic model of MARS and proposing a robust and efficient self-reconstruction algorithm that maximizes the controllability margin at each intermediate stage. Specifically, we develop algorithms to compute optimal, controllable disassembly and assembly sequences, enabling robust self-reconfiguration. Finally, we validate our method in several challenging fault-tolerant self-reconfiguration scenarios, demonstrating significant improvements in both controllability and trajectory tracking while reducing the number of assembly steps. The videos and source code of this work are available at https://github.com/RuiHuangNUS/MARS-Reconfig/

Modular Aerial Robot Systems (MARS) consist of multiple drone units that can self-reconfigure to adapt to various mission requirements and fault conditions. However, existing fault-tolerant control methods exhibit significant oscillations during docking and separation, impacting system stability. To address this issue, we propose a novel fault-tolerant control reallocation method that adapts to an arbitrary number of modular robots and their assembly formations. The algorithm redistributes the expected collective force and torque required for MARS to individual units according to their moment arm relative to the center of MARS mass. Furthermore, we propose an agile trajectory planning method for MARS of arbitrary configurations, which is collision-avoiding and dynamically feasible. Our work represents the first comprehensive approach to enable fault-tolerant and collision avoidance flight for MARS. We validate our method through extensive simulations, demonstrating improved fault tolerance, enhanced trajectory tracking accuracy, and greater robustness in cluttered environments. The videos and source code of this work are available at https://github.com/RuiHuangNUS/MARS-FTCP/

Continuous Group Key Agreement (CGKA) is the core of a new generation of End-to-End secure (E2E) cryptographic multi-party applications. CGKA allows the members in a dynamic group to agree on the current state for continuous communicating. The first CGKA protocol deployed in practical E2E applications is Inside-Secure TreeKEM (ITK), in which members use flood broadcasting to transition to the same new state for subsequent communications. However, flood broadcasting requires spread of a large amount of messages, while only a small part of the messages is needed for one specific member. This would incur substantial communication costs. To reduce the communication costs, Server-Aided ITK (SAIK) was proposed. SAIK employs a server to split the whole uploaded messages into multiple pieces, and deliver each piece to a specific member, thereby saving bandwidth of members. However, SAIK relies on a central server and hence is vulnerable to the single-point-of-failure problem. The problem is that if the server is unavailable, it will cause a sharp reduction in efficiency and increasing cost. In this work, we first formalize CGKA with smart contract (ScCGKA), which replaces the central server with smart contracts to solve the single-point-of-failure problem. We give a concrete construction of ScCGKA, dubbed the improved ITK with smart contract (ScITK). ScITK is constructed on ITK and can be deployed in real-world E2E applications. In ScITK, participants collaboratively negotiate and deploy a smart contract on the Ethereum blockchain to perform the splitting-delivering procedure. We give a formal security model to capture security properties that CGKA needs to achieve and a correctness property. The comparison between our ScITK and existing approaches shows that ScITK not only reduces communication cost, but also removes the server’s costs.