A Bio-inspired Climbing Robot with Directional Dry Adhesion for Reduced-Gravity Mobility

Abstract

This study presents a six-legged climbing robot equipped with gecko-inspired dry adhesives and a ball-joint foot mechanism designed for stable locomotion on inclined and vertical surfaces. Each leg has two degrees of freedom (hip swing and foot lift) controlled via a Raspberry Pi 4, PWM-driven microservos, and adaptive slip tracking through an MPU-6050. For directional adhesion, custom PDMS footpads were molded from 7 µm diffraction gratings, allowing shear-based attachment without external power. The robot was tested under full gravity and a simulated reduced-gravity gantry mechanism decomposed of gravitational force vectors. Experiments were performed across slip angles from 0° to 90° on smooth acrylic surfaces, and four-legged and six-legged configurations were compared. Results show that the six-legged robot consistently achieved greater displacement, velocity, and efficiency than the four-legged robot. At 0° slip, forward displacement was increased with adhesion by ~60% compared with that without adhesion (18.72 ± 0.5 cm vs. 11.68 ± 0.4 cm). At 90° under reduced gravity, the six-legged robot maintained 56.3 ± 8.0% efficiency, compared to 0% for the quadruped, confirming the role of redundant contact points in sustaining locomotion. However, at 10° slip, efficiency decreased below 42% due to inconsistency in detachment and limits of rigid foot conformity. These findings validate the role of increased contact points and distributed adhesion in supporting locomotion in complex gravitational environments, making the system suitable for planetary exploration and on-orbit servicing. Future work will incorporate compliant toe mechanisms, active peeling strategies, and closed-loop gait control to improve detachment, load sharing, and adaptive locomotion.

Received: 22 July 2025 | Revised: 23 September 2025 | Accepted: 29 September 2025

Conflicts of Interest

The authors declare that they have no conflicts of interest to this work.

Data Availability Statement

Data are available from the corresponding author upon reasonable request.

Author Contribution Statement

Motaz Hassan: Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration. Oluwafemi Fayomi: Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration. Joshua Faust: Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing – original draft, Writing – review & editing, Visualization. Ajay Mahajan: Methodology, Software, Formal analysis, Investigation, Resources, Writing – original draft, Writing – review & editing, Visualization.