Dynamic Quadrupedal Legged and Aerial Locomotion via Structure Repurposing

TL;DR

The paper tackles the challenge of integrating dynamic legged locomotion with aerial flight in a single platform by employing structure repurposing to reuse limb mass as flight thrust. Husky v.2 is presented as a lighter, hardware-focused implementation that enables knee-mounted propellers and posture manipulation to switch between quadrupedal trotting and hovering. The authors provide a detailed hardware design, mass-thrust trade-off analysis with $m_1 = m_b + 2m_L$, $m_2 = m_1 + 2m_t$, $m_3 = m_2 + 2m_t$ and a thrust-to-weight relationship $\beta' = \left(2 - \frac{4m_t}{m_3}\right)\beta$, and report untethered demonstrations of dynamic trotting and stable hover using a Raibert-inspired controller and standard flight control. This work demonstrates a practical route toward versatile multi-modal robots capable of navigating cluttered ground and aerial environments, with potential applications in delivery and search-and-rescue scenarios, while outlining future work on unified control and perception-assisted autonomous operation. The thrust-to-weight ratio is shown to remain favorable ($\beta \approx 2$) even as thruster mass is integrated, enabling stable flight alongside dynamic legged locomotion.

Abstract

Multi-modal ground-aerial robots have been extensively studied, with a significant challenge lying in the integration of conflicting requirements across different modes of operation. The Husky robot family, developed at Northeastern University, and specifically the Husky v.2 discussed in this study, addresses this challenge by incorporating posture manipulation and thrust vectoring into multi-modal locomotion through structure repurposing. This quadrupedal robot features leg structures that can be repurposed for dynamic legged locomotion and flight. In this paper, we present the hardware design of the robot and report primary results on dynamic quadrupedal legged locomotion and hovering.

Figures (8)

• Figure 1: This work explores multi-modal dynamic-legged-aerial locomotion through appendage repurposing.
• Figure 2: A: System Overview. The system is composed of the main body where the electronics are mounted, and the leg sub-assemblies. The mounting frames and linkages are made out of 3D printed plastic (Markforged Onyx and reinforcing materials) and carbon fiber tubes/plates, respectively. B: Leg Design. The lower leg, shown as the tibia and fibula linkages, are parallel linkages which is actuated at the knee by the servo. The robot is capable of transforming into the UAV mode and use the propellers mounted at the knee joint for aerial mobility. C: Electronics Architecture: A Lithium Polymer (LiPo) battery powers the entire system, which consists of 4 propeller motors and 12 joint servos. The microcontroller units, which consists of the flight controller and an on-board computing unit, coordinates the input/output of the system to interface with the sensors and controller commands and stabilize the robot.
• Figure 3: Demonstrates Husky v.2's structure repurposing during transitions between dynamic trotting and hovering, and vice versa.
• Figure 4: Shows Husky v.2 recovers from a gentle push on its torso during untethered trotting. The leg trajectories are shown as the red lines.
• Figure 5: The figure illustrates the vehicle's orientation (roll, pitch, and yaw) angles along with the motor output after the transition to aerial mode. The vehicle initiates takeoff at around the 10-second mark and successfully lands at approximately 25 seconds. The motor output subplot displays the throttle levels, expressed as percentages.