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Avian-Inspired Claws Enable Robot Perching or Walking

Mohammad Askari, Won Dong Shin, Damian Lenherr, William Stewart, Dario Floreano

TL;DR

This work tackles the problem of extending UAV capability beyond flight to include passive perching and walking by introducing an avian-inspired claw that combines a Hoberman linkage leg with a Fin Ray claw. The design leverages the UAV's own weight to passively wrap around a perch for stable perching and to hyperextend for ground locomotion, delivering a lightweight, underactuated solution. The authors provide sizing guidelines and a static performance model, and validate the approach through perching experiments on various perch geometries and walking tests with actuated legs, showing stable behavior up to a 19.4° lean on small perches and meaningful walking distances with increased support polygons. This multimodal claw system expands the operational envelope of UAVs in cluttered environments and for extended missions such as search and rescue, recharge, or fixed-sensor deployment.

Abstract

Multimodal UAVs (Unmanned Aerial Vehicles) are rarely capable of more than two modalities, i.e., flying and walking or flying and perching. However, being able to fly, perch, and walk could further improve their usefulness by expanding their operating envelope. For instance, an aerial robot could fly a long distance, perch in a high place to survey the surroundings, then walk to avoid obstacles that could potentially inhibit flight. Birds are capable of these three tasks, and so offer a practical example of how a robot might be developed to do the same. In this paper, we present a specialized avian-inspired claw design to enable UAVs to perch passively or walk. The key innovation is the combination of a Hoberman linkage leg with Fin Ray claw that uses the weight of the UAV to wrap the claw around a perch, or hyperextend it in the opposite direction to form a curved-up shape for stable terrestrial locomotion. Because the design uses the weight of the vehicle, the underactuated design is lightweight and low power. With the inclusion of talons, the 45g claws are capable of holding a 700g UAV to an almost 20-degree angle on a perch. In scenarios where cluttered environments impede flight and long mission times are required, such a combination of flying, perching, and walking is critical.

Avian-Inspired Claws Enable Robot Perching or Walking

TL;DR

This work tackles the problem of extending UAV capability beyond flight to include passive perching and walking by introducing an avian-inspired claw that combines a Hoberman linkage leg with a Fin Ray claw. The design leverages the UAV's own weight to passively wrap around a perch for stable perching and to hyperextend for ground locomotion, delivering a lightweight, underactuated solution. The authors provide sizing guidelines and a static performance model, and validate the approach through perching experiments on various perch geometries and walking tests with actuated legs, showing stable behavior up to a 19.4° lean on small perches and meaningful walking distances with increased support polygons. This multimodal claw system expands the operational envelope of UAVs in cluttered environments and for extended missions such as search and rescue, recharge, or fixed-sensor deployment.

Abstract

Multimodal UAVs (Unmanned Aerial Vehicles) are rarely capable of more than two modalities, i.e., flying and walking or flying and perching. However, being able to fly, perch, and walk could further improve their usefulness by expanding their operating envelope. For instance, an aerial robot could fly a long distance, perch in a high place to survey the surroundings, then walk to avoid obstacles that could potentially inhibit flight. Birds are capable of these three tasks, and so offer a practical example of how a robot might be developed to do the same. In this paper, we present a specialized avian-inspired claw design to enable UAVs to perch passively or walk. The key innovation is the combination of a Hoberman linkage leg with Fin Ray claw that uses the weight of the UAV to wrap the claw around a perch, or hyperextend it in the opposite direction to form a curved-up shape for stable terrestrial locomotion. Because the design uses the weight of the vehicle, the underactuated design is lightweight and low power. With the inclusion of talons, the 45g claws are capable of holding a 700g UAV to an almost 20-degree angle on a perch. In scenarios where cluttered environments impede flight and long mission times are required, such a combination of flying, perching, and walking is critical.
Paper Structure (13 sections, 18 equations, 12 figures, 1 table)

This paper contains 13 sections, 18 equations, 12 figures, 1 table.

Table of Contents

  1. Introduction
  2. Related Work
  3. Leg and Claw Design
  4. Perching Characterization
  5. Legged Locomotion Characterization
  6. Conclusions
  7. Acknowledgements
  8. Model Assumptions
  9. Kinematic Analysis
  10. Four-bar Position Kinematics
  11. Static Force Equilibrium
  12. Squeezing Force Estimation
  13. Maximum Tilting Moment and Sustainable Angle

Figures (12)

  • Figure 1: Sample mission of a flying-perching-walking robot for search and rescue. The inset views show comparisons of the feet of a purple finch and the robotic equivalent in different configurations. Photo credits: Rejean Aline; Claude Laprise; Olga Pink - Adobe Stock.
  • Figure 2: Leg and claw design. (a) Geometric parameter sizing of the claw is done in the perched configuration. The CAD of the claw was sized based on the calculations presented in the bottom of the figure. (b) Photos of the assembled claw in perched (left) and hyperextended (right) modes. (c) Mechanical advantage profiles of the Hoberman linkage over a range of base rib angles ($\epsilon$) for different $\gamma$ values. Grey shading shows whether the claw is within the perched or the hyperextended region. The vertical black line at -5 degrees indicates the singularity point where the claw switches between the two modes. The other vertical lines show the limits of claw geometry ($\gamma = 150°$) selected for this project. (d) Diagram and geometric parameters of the linkage.
  • Figure 3: (a) Split perch experimental setup. Two halves of the split perch encompass the ATI Nano17 loadcell. Weights are mounted to a wooden rod, which press on the talon-less claw, which converts the weight into a squeezing force measured by the load cell. (b) Diagram of the claw in perched configuration. (c) Plot of the estimated and measured squeezing force as a function of weight. The shaded regions represent the standard deviation of 10 measurements.
  • Figure 4: (a) Slip resistance experimental setup. (b) Schematic force diagram of the model of the experiment (see Supplementary Text for more details). This illustration shows how the moment due to the mass of the UAV ($M_w$) is counteracted by the moment due to the friction of the claw ($M_f$) grasping the perch. (c) Maximum tilting angle and moment measurements for different weights and perch diameters. The plot at the top shows variation in the moment over time for the case of 300g weight on a 40mm perch. The shaded regions represent the standard deviation of repeated experiments.
  • Figure 5: Perching experiment with a manually piloted quadcopter equipped with a set of two claws. (top) vertical distance from the perch and (middle) the pitch angle over time. (bottom) Snapshots from the video corresponding to different instances of the perching maneuver. Instant (i) shows the UAV in flight before touchdown, and (ii) it makes contact with the wooden perch. (iii) shows when the claws are fully closed and firmly grip the perch. At (iv) the UAV tilts back when the thrust is significantly reduced, and when the propellers are completely stopped (v), the UAV remains perched at 11.6 degrees.
  • ...and 7 more figures