A Small Rotorcraft Capable of Continuous Monopedal Hopping

Description

With numerious applications such as surveying and payload delivery, research in micro, human-friendly aerial vehicles has received immense attention. These tiny robots have begun to impact the uptake of robots for civilian and service applications. However, compared to conventional aircraft, centimeter-scale flying robots suffer from a fundamental demotion in aerodynamic and actuation efficiency. The aggravated energetic cost of staying airborne acutely restricts flight range and endurance. In order to overcome the energetic constraint and simultaneously widen the functionalities, research in multimodal locomotion of aerial robots has gathered interest. Surface locomotion or perching becomes favorable for small vehicles due to the increased surface-to-weight ratio. Hybrid terrestrial locomotion has been demonstrated as a promising and efficient strategy for robots to traverse on the ground. Nevertheless, to date, small legged quadrotors are usually constructed by directly incorporating two distinct mechanisms with few multi-functional components, leading to excessive added weight and inefficiency. Furthermore, they are yet to display the dynamic movement and agility demonstrated by conventional hopping and legged robots. This proposed research introduces the Hopcopter—a sub-50-g quadcopter with a single passive compliant leg. The rotorcraft is able to hop dynamically and efficiently as it uniquely uses the existing propellers for terrestrial locomotion. This proposal elaborates the integrative approach and the plan to realize agile hopping maneuvers in three steps. First, the hopping strategy and dynamic models are devised based on the identification experiments conducted with a preliminary prototype. With entirely passive dynamics in the stance phase, the robot relies on the propulsion in the aerial phase to regulate the energy level and maintain stability using the velocity feedback from external cameras. Second, lightweight optic flow and time-of-flight sensors are integrated to obtain control autonomy. The added onboard sensors, when fused with IMU readings, supply the estimate of the body-centric velocity and replace previous external feedback required for the robot to hop stably at the desired horizontal speed. Finally, to take full advantage of the aerial propulsion, a Hopcopter with inverted propellers is proposed to raise the hopping agility. While hopping, the downward aerodynamic thrust applied in the aerial phase accelerates the descent and shortens the stride duration beyond the ballistic limit confronted by conventional hopping robots that depend on the ground reaction force for actuation. The enhanced agility translates to an increase in hopping speed. It is perceivable that the proposed research will contribute to advances of micro aerial robots by the introduction of the agile hopping ability and associated reduction in the cost of transport, broadening the operating scenarios and applications of small aerial vehicles. Scientific merits will come from (i) the integrated design of a hybrid flying and hopping vehicle and the accompanied hopping methods; (ii) the demonstration of stable hopping with control autonomy of a sub-50-g rotorcraft; and (iii) the use of aerial propulsion to boost the hopping agility to highlight the capability of the hybrid platform.