Assistant Professor Sameh Eisa and his team at UC’s College of Engineering and Applied Science have designed a flapping-wing drone modeled after the unique flight mechanics of moths. These insects exhibit remarkable flight capabilities, including the ability to hover steadily in one place, fly backward, and perform nuanced adjustments to compensate for environmental disturbances such as wind or moving obstacles. Mimicking these abilities, the drone maintains a stable distance and orientation relative to a moving light source, much like moths instinctively navigate toward a flame. The key to this capability lies not in heavy computation or sophisticated AI but in an extremum-seeking feedback control system that continuously optimizes flight performance through simple, biologically plausible feedback loops.

Prior research has extensively explored fixed-wing and rotary drones, but the tiny flapping-wing drones represent a relatively nascent field, influenced heavily by the biomechanics of insects and hummingbirds. What sets this new mothlike drone apart is its minimalistic control strategy. Traditional autonomous drones rely on global positioning systems, preprogrammed flight paths, or onboard AI to navigate. In contrast, the University of Cincinnati’s model operates by evaluating performance in real time and making incremental adjustments to wing flapping frequencies and amplitudes. This extremum-seeking feedback allows the drone to stabilize itself and pursue the optimal flight state, dynamically responding as if it were a living creature with an embedded natural controller.

Flapping-wing drones control their three-dimensional orientation—roll, pitch, and yaw—through independent wing movements. However, these wing beats are so rapid they blur to the human eye, resembling the frantic motion of a hummingbird’s wings. By modulating these subtle wing motions, the drone adjusts flight vectors instantaneously, maintaining equilibrium and position relative to its target. The extremum-seeking framework exploits this fine control to minimize deviation from the target state and optimize stability without the need for complex algorithms, sensors, or external positioning data.

The research team’s findings build upon mathematical modeling and experimental studies conducted in Eisa’s Modeling, Dynamics and Control Lab. Here, doctoral student Ahmed Elgohary and graduate researcher Rohan Palanikumar have demonstrated through simulations and live experiments how an extremum-seeking control system naturally replicates the hovering prowess of various insects, including moths, bumblebees, dragonflies, hoverflies, and even hummingbirds. This system operates in a continuous feedback loop, measuring flight performance metrics and using measured perturbations—such as the intentional wobble introduced into the drone’s flight—to assess and improve its positional accuracy in real time.

The implications of this research extend beyond mere biomimicry. By distilling insect flight control to this elegant extremum-seeking principle, the researchers open new avenues for the design of autonomous unmanned aerial systems capable of stable flight in cluttered, dynamic environments. These drones, with miniaturized and efficient control architectures, have the potential to revolutionize covert surveillance, environmental monitoring, and search-and-rescue operations, offering flight capabilities and maneuverability far surpassing conventional rotorcraft.

Importantly, this advancement challenges long-held assumptions about the necessity of complex brain functions in small flying creatures to achieve agile flight. The study suggests that the nervous systems of these insects may employ feedback control strategies akin to extremum-seeking rather than relying on extensive data processing or sophisticated cognition. Such a discovery not only contributes to robotics and aerospace engineering but also offers profound insights into neurobiology and evolutionary biomechanics, suggesting that effective flight control is achievable with remarkably simple, robust feedback loops.

The drone itself is equipped with four slender wings made of wire and fabric, delicately constructed to mimic the flexible and deformable structure of insect wings. Like the nectar-loving hummingbird clearwing moth, which moves its wings in an elegant figure-eight pattern to generate lift on both the downstroke and upstroke, the drone’s flexible wings enable optimized lift and maneuverability. This design ensures the flapper drone can maintain its position with minimal energy input, maximizing flight efficiency.

Control of the drone was demonstrated live in a specialized flight lab, where protective netting ensures safety during experimental flights. Attempts to manually control the drone proved to be less stable and reliable than the autonomous extremum-seeking system, underscoring the efficacy of the biological control inspiration. Once activated, the drone quickly achieved stable hovering despite a deliberate wobble introduced to generate continuous perturbations for feedback analysis. This wobble is a fundamental part of the control strategy, enabling the drone to constantly evaluate and adjust its flight dynamics.

The team’s results were recently published in the journal Physical Review E, emphasizing the experimental validation of extremum-seeking feedback as a natural and stable control method for hovering flight. Their simulations and experiments bridge gaps across theoretical biology, control theory, and applied robotics, highlighting how complex behaviors emerge from simple control laws. The system’s real-time, model-free operation challenges the dominance of AI-based navigation algorithms, offering a promising alternative for scalable, lightweight flying robots.

Looking forward, the researchers imagine applications where swarms of such mothlike drones could perform reconnaissance or environmental sensing tasks with exceptional energy efficiency and agility in GPS-denied or visually complex environments. The autonomy and stability achieved through extremum-seeking control could make possible a new generation of micro aerial vehicles that operate independently without external infrastructure or computational overhead.

The moth drone project embodies the synthesis of biology-inspired engineering and advanced control theory, offering an elegant demonstration that nature’s strategies continue to inspire innovation. The research not only elucidates the mysteries behind the aerial feats of insects with microscopic brains but also charts a path for future robotics that prioritize simplicity, efficiency, and robustness. As these miniaturized flapping-wing drones take flight, they bring us ever closer to replicating—and perhaps surpassing—the marvels of natural flight.

Article Title: Hovering flight in flapping insects and hummingbirds: A natural real-time and stable extremum-seeking feedback system

News Publication Date: 22-Oct-2025

Image Credits: Michael Miller

Keywords: Complex networks, Applied mathematics, Artificial intelligence, Robot control, Military technology

Fast forward ten years, the focus at SUTD has drastically shifted. Rather than pursuing further efficiency improvements for the multi-rotor design, Assoc Prof Foong and his research team looked towards nature for inspiration, specifically the aerodynamic prowess of the samara—those spiral-winged seeds released by maple trees. Embracing a minimalist approach, they engineered a lightweight monocopter that utilizes a single actuator to enable efficient and controllable flight.

In their study published in the prestigious IEEE Robotics and Automation Letters, titled “Design and optimization of a samara-inspired lightweight monocopter for extended endurance,” the researchers disclosed their meticulous design process. The outcome is astonishing: a drone weighing only 32 grams capable of hovering autonomously for 26 minutes. This achievement far exceeds the performance metrics of typical drones within the same weight class, thereby challenging conventional understandings of drone performance.

As Assoc Prof Foong elaborated, the rationale behind this design transformation is rooted in the inherent inefficiencies associated with scaling down technologies. Small drones often succumb to poor endurance primarily due to the limitations of their small propellers, which generate finite thrust at high power consumption. Their innovative monocopter design addresses these limitations by adopting principles observed in nature, effectively reorienting drone design philosophy towards maximizing efficiency rather than merely increasing power.

Nature’s samaras utilize a clever approach, leveraging passive stability while crafting an aerodynamically efficient flight characteristic. Assoc Prof Foong emphasized that every portion of the maple seed contributes to its lift—an insight that was instrumental in developing an airframe design where each component serves a purpose without redundancy. This leads to a design ethos that champions resource efficiency and simplicity over excessive intricacy.

The integration of artificial intelligence has also played a vital role in this engineering endeavor. While inspiration was drawn from the natural world, the optimisation of wing geometries and balancing mass distribution was significantly enhanced through advanced AI-driven methodologies. Such techniques allow researchers to rigorously explore various design configurations efficiently, sidestepping the need for exhaustive manual testing.

Unlike traditional quadcopters that depend on multiple rotors for flight, the monocopter developed by the SUTD team demonstrates that a solo actuator suffices. This pivotal component spins the winged body to maintain stability via passive dynamics while simultaneously generating lift through the drone’s expansive airfoil design. The resulting structural integrity reflects a profound simplicity that belies its effective performance.

The optimization process behind the monocopter was exhaustive and intricately detailed. Combining classical aerodynamic theories with contemporary real-world performance models, researchers employed a surrogate optimization method, a cutting-edge data-driven algorithm to refine every aspect of the monocopter’s design. Ultimately, their efforts yielded a drone with a power loading ratio of 9.1 grams per watt, setting new standards for micro air vehicles in terms of both size and hovering capability.

Research Fellow Cai Xinyu, who contributed to the drone’s development, expressed the excitement of their achievement, noting the viability of small aerial robotics achieving endurance benchmarks traditionally expected from larger systems. This breakthrough demonstrates that advancement in drone technology does not solely hinge on increased size but can be achieved through refined engineering and intelligent design practices.

The potential applications for this monocopter are vast and varied. Its lightweight and enduring characteristics herald possibilities in low-cost, long-duration missions. Among these is the exciting proposition of a resilient, reusable radiosonde— a weather-monitoring instrument traditionally deployed via balloons. This innovative approach recently garnered recognition as the Sustainability Winner at the James Dyson Award for 2024, further validating the environmental impact and practical utility of this aerial technology.

While the current prototype leverages readily available commercial components, there are ambitious plans for the future. Research teams are aiming to explore bespoke materials to enhance the performance of the monocopter further while broadening its payload capacity and extending flight duration without significantly augmenting its weight. The evolving design will also consider bio-inspired morphologies, ensuring that every innovation continues to push the limits of drone capabilities.

The story of the SG60 monocopter encapsulates an impressive technological journey that illustrates not only continuity but a significant departure from traditional drone engineering paradigms. With aspirations set high, the SUTD team envisions developing a prototype capable of achieving over 60 minutes of flight duration, aptly commemorating Singapore’s upcoming 60th anniversary. In an emphatic statement, Assoc Prof Foong summarized their mission by highlighting that their work encapsulates not just technological innovation but a sustainable vision for the future of aerial robotics.

In summary, the development of the samara-inspired monocopter signifies a formidably innovative leap in drone technology, underpinned by a rigorous research approach, clear inspiration from nature, and the impactful integration of artificial intelligence into the design process. This project stands as a testament to the potential of biomimicry and advanced engineering in transcending previously understood limitations of drone technologies, providing a vision that challenges the conventions of scale and efficiency.

Subject of Research: Samara-Inspired Monocopter Design
Article Title: Small but mighty: A biomimetic idea takes flight
News Publication Date: October 2023
Web References: IEE Robotics and Automation Letters
References: N/A
Image Credits: Credit: SUTD

Keywords

Biomimetic drones, monocopter design, drone technology, lightweight drones, SUTD, AI in design, sustainable engineering.