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.

翻译：大多数鸟类能够在空中与陆地环境之间无缝切换。前肢主要进化为用于飞行的翅膀，而后肢则承担行走、跳跃、跃起以及为转入飞行状态而进行的跳跃起飞等多种功能。这些能力启发工程师们致力于为飞行机器人实现类似的多模态运动能力，从而拓展其在多样化环境中的应用范围。然而，在复现具有不同运动学与推进特性的多步态（如行走与跳跃）多模态运动的同时，保持适于飞行的轻量化质量，仍面临诸多挑战。机械复杂性与多功能性之间的权衡限制了现有大多数飞行机器人仅能实现一种额外的运动模式。本文通过RAVEN（Robotic Avian-inspired Vehicle for multiple ENvironments）机器人克服了复杂度与多功能性之间的权衡，该机器人利用其受鸟类启发的多功能腿部实现快速跳跃起飞、地面行走以及跨越障碍与沟壑的跳跃，其多模态运动方式与鸟类相似。我们证明，跳跃起飞对初始飞行起飞速度有显著贡献，并且值得注意的是，其能量效率高于仅依靠螺旋桨的起飞方式。我们的分析表明，适应不同运动策略的鸟类在腿部与身体的质量分布上存在重要权衡：对具有多模态步态需求的陆栖鸟类而言，其腿部质量占比更高。多功能机器人腿部通过自主起飞与多模态步态，为传统固定翼飞机在复杂地形中的部署拓展了新的可能性。