A Modular Aerial System Based on Homogeneous Quadrotors with Fault-Tolerant Control

TL;DR

The paper tackles the limitations of standard quadrotors' under-actuation by proposing IdentiQuad, a modular aerial system built from homogeneous quadrotor modules that can reconfigure to provide up to six controllable DOF. It introduces a general, configuration-aware geometric controller with energy-balancing optimization and a fault-tolerant strategy for in-flight rotor failures, validated in physics-based simulations across multiple assembly configurations. Key contributions include (1) a modular homogeneous architecture enabling full actuation, (2) a universal controller that balances energy across modules and adapts to rotor faults, and (3) a fault-tolerant framework that preserves essential task-space tracking under degraded actuation. The findings demonstrate that the modular assembly can achieve complex six-DOF trajectories, maintain position tracking under failures, and extend operating time through energy balancing, highlighting significant practical impact for reconfigurable aerial robotics without complex heterogeneous hardware. Future work points to real-world field trials, validating wrench capabilities, and extending fault tolerance to configurations with fewer than four controllable DOF.

Abstract

The standard quadrotor is one of the most popular and widely used aerial vehicle of recent decades, offering great maneuverability with mechanical simplicity. However, the under-actuation characteristic limits its applications, especially when it comes to generating desired wrench with six degrees of freedom (DOF). Therefore, existing work often compromises between mechanical complexity and the controllable DOF of the aerial system. To take advantage of the mechanical simplicity of a standard quadrotor, we propose a modular aerial system, IdentiQuad, that combines only homogeneous quadrotor-based modules. Each IdentiQuad can be operated alone like a standard quadrotor, but at the same time allows task-specific assembly, increasing the controllable DOF of the system. Each module is interchangeable within its assembly. We also propose a general controller for different configurations of assemblies, capable of tolerating rotor failures and balancing the energy consumption of each module. The functionality and robustness of the system and its controller are validated using physics-based simulations for different assembly configurations.

Figures (8)

• Figure 1: An assembly of $7$ IdentiQuads, where the rotor marked with a red circle fails at time $t=1s$ and the two rotors marked with dark blue circles fail at time $t = 5s$.
• Figure 2: Design of an IdentiQuad module. Left: All four connectors have the same relative angle $\alpha$ to the frame. Right: A relative angle $\beta \in [0, 2 \pi)$ can be achieved by aligning magnet $1b$ with different magnets from $1a$ to $4a$.
• Figure 3: An overview of the proposed general controller for $n$-IdentiQuads assembly with energy balancing among modules and fault-tolerant in case of in-flight rotor failures.
• Figure 4: Left: A $3$-IdentiQuads assembly tracking three-dimensional figure-eight trajectory while maintaining its orientation. Middle: A $4$-IdentiQuads assembly tracking a five DOF trajectory with the desired roll angle $\phi_d$ range from $0$ to $2 \pi$, achieving a full circle angle tracking. Right: A $5$-IdentiQuads assembly start with different battery voltage, the dark blue marked module start with $70\%$ of its full battery voltage. The red circle marked rotor fails at time $t=5s$.
• Figure 5: Simulation results of the $3$-IdentiQuads assembly tracking a six DOF trajectory.