Fast ground-to-air transition with avian-inspired multifunctional legs (2412.02389v1)

Abstract: Most birds can navigate seamlessly between aerial and terrestrial environments. Whereas the forelimbs evolved into wings primarily for flight, the hindlimbs serve diverse functions such as walking, hopping, and leaping, and jumping take-off for transitions into flight. These capabilities have inspired engineers to aim for similar multi-modality in aerial robots, expanding their range of applications across diverse environments. However, challenges remain in reproducing multi-modal locomotion, across gaits with distinct kinematics and propulsive characteristics, such as walking and jumping, while preserving lightweight mass for flight. This tradeoff between mechanical complexity and versatility limits most existing aerial robots to only one additional locomotor mode. Here, we overcome the complexity-versatility tradeoff with RAVEN (Robotic Avian-inspired Vehicle for multiple ENvironments), which uses its bird-inspired multi-functional legs to jump rapidly into flight, walk on ground and hop over obstacles and gaps similar to the multi-modal locomotion of birds. We show that jumping for take-off contributes substantially to initial flight take-off speed and, remarkably, that it is more energy-efficient than solely propeller-based take-off. Our analysis suggests an important tradeoff in mass distribution between legs and body among birds adapted for different locomotor strategies, with greater investment in leg mass among terrestrial birds with multi-modal gait demands. Multi-functional robot legs expand opportunities to deploy traditional fixed-wing aircraft in complex terrains through autonomous take-offs and multi-modal gaits.

• The paper introduces RAVEN, a robotic system that leverages avian-inspired leg design to achieve fast ground-to-air transitions.
• It details a simplified two-segment leg with a torsional spring that stores and releases energy, improving take-off performance by 25%.
• The innovative mechanism boosts jumping efficiency by 9.7-fold and contributes 91.7% of the required take-off speed, enhancing terrain versatility.

Avian-Inspired Multifunctional Legs for Aerial Robots: Insights from RAVEN

The paper in question presents an innovative exploration of avian-inspired robotic systems, focusing on the development and analysis of multifunctional legs designed to enable rapid transitions from ground to air. This work introduces the Robotic Avian-inspired Vehicle for multiple ENvironments (RAVEN), which synthesizes biologically inspired principles to achieve versatile locomotion akin to birds. The paper elucidates the design process, mechanical innovations, and the performance implications of adopting avian-inspired leg mechanics in aerial robotics.

Design and Mechanical Complexity

The authors address the longstanding challenge in aerial robotics of balancing mechanical complexity with locomotor versatility. Traditional designs have been constrained by a trade-off between integrating multiple locomotion modes and maintaining lightweight structures essential for efficient flight. RAVEN circumvents this by incorporating simplified two-segment legs, deliberately eschewing the higher complexity of full multi-segment bird anatomy. The innovation lies in its targeted distribution of leg mass and the incorporation of a torsional spring at the ankle joint, enabling significant energy storage and release during take-off.

Locomotion Performance

The core contribution of RAVEN is its demonstrated capacity for energy-efficient and rapid take-offs facilitated by its bird-inspired legs. Experiments revealed that the legs are crucial to achieving a high initial flight speed, contributing approximately 91.7% of the required speed of 2.4 m/s at take-off. This performance markedly surpasses that of purely propeller-based take-off strategies, underscoring the efficiency of integrating jumping legs. Furthermore, the authors report a 25% improvement in jumping speed due to the power-amplifying mechanism at the ankle joint.

Energetic and Kinematic Efficiency

The numerical results provided illustrate a striking enhancement in energy efficiency, with the jumping take-off strategy displaying a 9.7-fold increase in energetic efficiency compared to standing take-offs. The implementation of RAVEN's multifunctional legs allows the robotic platform to negotiate a range of terrains while maintaining operational energy efficiency comparable to that observed in specific ground-dwelling birds.

Implications for Aerial Robotics

The implications of this research are multifaceted. Practically, RAVEN's design offers a compelling solution to deploy unmanned aerial vehicles in complex terrains without requiring runways, enhancing their utility in military, rescue, and remote sensing applications. Theoretically, the paper contributes to the ongoing discourse on bio-mimicry in robotics, highlighting the potential to adapt avian locomotion strategies to robotic systems. The results suggest an optimal distribution of muscle mass in robotic legs can parallel avian adaptations, which could facilitate greater versatility in robotic deployments.

Speculation on Future Developments

Considering the significant advantages exhibited by RAVEN, future work could explore scaling these principles to larger robotic platforms, examining the boundaries of these biophysical adaptations. Moreover, research into further reducing control complexity while increasing functional capabilities could extend the applicability of avian-inspired robots in even more dynamic and variable environments.

In summary, this paper succeeds in demonstrating the viability and enhanced performance of integrating avian-inspired multifunctional legs within aerial robotic systems, providing a robust foundation for future explorations in the multi-modal capabilities of autonomous systems.