Hopping Aerial Robots: Reaching New Heights across Size Scales through Thrust-based and Parallel Elastic Actuation

The landscape of robotics and autonomous systems has seen remarkable advancements, particularly in the development of mobile robots. Micro aerial vehicles are enabling diverse applications ranging from infrastructure inspection to disaster response. However, limited payload capacity and flight endurance hinder their functionality and real-world viability. Meanwhile, terrestrial robots can carry heavier loads but lack aerial maneuverability in overcoming obstacles and accessing elevated spaces. To address these limitations of aerial and terrestrial robots, recent research has begun exploring platforms with both flying and ground capabilities. However, most hybrid designs rely on directly incorporating separate mechanisms for each locomotion mode, resulting in inefficient performance. The added mass and complexity of actuated legs or wheels compromise their mobility and flight efficiency. To circumvent these challenges, our team has recently developed the Hopcopter—a lightweight quadcopter capable of continuous hopping on a single leg. By integrating a single passive, springy leg to a quadcopter, an existing flight platform can be transformed into a hopping robot, with the existing motor-driven propellers serving as the sole actuators for both modes of operation. This synergistic approach minimizes weight and power consumption, without sacrificing the efficiency of the vehicle. This proposed research seeks to expand on the Hopcopter’s capabilities, exploring the potential of thrust-based and parallel elastic actuation across different size scales in three steps. The first task creates the first subgram robot capable of continuous hopping by integrating a passive compliant leg with an existing insect-scale flapping-wing platform. This is accomplished by leveraging the mechanical simplicity of a passive leg and lowered actuation power of thrust-based hopping. Second, the payload capacity of thrust-based hopping rotorcraft is to be radically expanded. Incorporation of bidirectional thrusters on a multirotor robot boosts payload capacity significantly beyond the thrust-to-weight ratio. A drone is anticipated to carry a payload multiple times its own weight by hopping, enhancing its functionality for real-world applications. Furthermore, autonomous operation is attained as the payload includes a suite of sensors and computational units for visual-inertial odometry. Finally, a parallel elastic hopper with the ability to modulate energy and adjust hop height is proposed. The actuated leg prolongs the energy accumulation timeframe, leading to higher jumps. One key component is the use of a latch mechanism that passively releases upon ground contact, facilitating continuous hopping rather than intermittent jumps. Through this approach, the goal is to demonstrate a remarkable hopping height of 3 m with a sub-100g robot, surpassing existing records. Upon completion, this research is expected to significantly advance the field of hybrid aerial-terrestrial locomotion, contributing to the development of efficient, versatile, and capable hopping robots. The key scientific contributions will come from (i) the demonstration of continuous hopping with a subgram insect-scale robot, a pioneering achievement in the realm of microrobots; (ii) a drastic increase in the payload limit of aerial robots brought by the hybrid hopping locomotion; and (iii) the design and realization of a parallel elastic hopper capable of modulating stored energy, setting new records in achievable hopping heights.