A Pin-Array Structured Climbing Robot for Stable Locomotion on Steep Rocky Terrain

Keita Nagaoka; Kentaro Uno; Kazuya Yoshida

cs.ROMar 17, 2026

A Pin-Array Structured Climbing Robot for Stable Locomotion on Steep Rocky Terrain

Authors: Keita Nagaoka, Kentaro Uno, Kazuya Yoshida

Organizations: The authors are with the Space Robotics Lab. (SRL) in Department of Aerospace Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan.

Abstract

Climbing robots face significant challenges when navigating unstructured environments, where reliable attachment to irregular surfaces is critical. We present a novel mobile climbing robot equipped with compliant pin-array structured grippers that passively conform to surface irregularities, ensuring stable ground gripping without the need for complicated sensing or control. Each pin features a vertically split design, combining an elastic element with a metal spine to enable mechanical interlocking with microscale surface features. Statistical modeling and experimental validation indicate that variability in individual pin forces and contact numbers are the primary sources of grasping uncertainty. The robot demonstrated robust and stable locomotion in indoor tests on inclined walls (10-30 degrees) and in outdoor tests on natural rocky terrain. This work highlights that a design emphasizing passive compliance and mechanical redundancy provides a practical and robust solution for real-world climbing robots while minimizing control complexity.

Figures & tables

Fig. 1: The pin-array unit passively adapts to irregular terrain shapes, enabling stable ground-gripping locomotion (top). The robot demonstrated stable adhesion performance on steeply inclined rocky terrain (bottom left) and was also deployed in a natural rough landscape (bottom right).

Fig. 2: Overview of the pin-array structured gripping technology: (a) hardware structure, (b) gripping mechanism, and (c) mechanical model of contact. A concave shape is exemplified as a terrain surface in (b); however, the same mechanism also works for convex shapes for gripping.

Fig. 3: Pin-array gripper unit design. Sixty-six pins are installed and driven by a single actuator.

Direction	Minimum Value [N]	Overall Average [N]
Normal	7.39	34.1
Tangential	6.11	21.1

TABLE I: Summary of holding force test results. Minimum and average holding forces were obtained in both the normal and tangential directions at various surface angles

\phi

Fig. 4: Holding force measurement setup. The pin-array gripper’s engaging performance was tested on various convex and concave objects with different ${\it\Phi}=\pm 30^{\circ},\pm 60^{\circ},\pm 90^{\circ}$ , while the height of the force application point from the terrain was kept constant at $d=0.14$ m.

Fig. 5: Simulation results validating the mechanical model of the pin-array gripper. The points correspond to the measurements from the holding force evaluation tests and are largely encompassed within the confidence interval.

Fig. 6: Hardware details of the developed pin-array structured mobile robot, consisting of six gripping units.

Fig. 7: Software system diagram of the robot.

Component	Model	Quantity
Robot
Embedded Computer	Intel NUC 13 Pro (NUC13ANKi7)	1
IMU	RT-USB-9axisIMU2	1
USB-Serial Converter	USD2	1
Lithium-ion Battery	Anker Prime Power Bank 27650mAh	1
Pin-Array Gripper Unit

TABLE II: Employed hardware components of the robot.

Fig. 8: Indoor climbing experiments conducted on an artificial rock field. The robot was tested on slopes of 10 ∘ , 20 ∘ , and 30 ∘ inclination (from left to right) to evaluate its climbing performance.

Fig. 9: Locomotion experiments in an outdoor natural rocky environment. Snapshots showing the robot’s traveling history from right to left (top) and the measured robot’s attitude fluctuations throughout the locomotion (bottom). The robot demonstrates stable traversal of the natural rocky terrain while maintaining a consistent posture (within $\pm 5^{\circ}$ in roll and pitch), owing to its highly terrain-adaptive locomotion.

Robot Locomotion

Robot locomotion studies how robots move efficiently and reliably across varied terrains, environments, and movement modes.

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LIMBERO: A Limbed Climbing Exploration Robot Toward Traveling on Rocky Cliffs

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The authors are with the Space Robotics Lab. (SRL) in Department of Aerospace Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan. · The author is with the National Institute of Applied Sciences of Toulouse, 31400 Toulouse, France.

Robot Locomotion Quadruped Locomotion Robotic Grasping

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In lunar and planetary exploration, legged robots have attracted significant attention as an alternative to conventional wheeled robots, which struggle to traverse rough and uneven terrain. To enable locomotion over highly irregular and steeply inclined surfaces, limbed climbing robots equipped with grippers on their feet have emerged as a promising solution. In this paper, we present LIMBERO, a 10 kg-class quadrupedal climbing robot that employs spine-type grippers for stable locomotion and climbing on rugged and steep terrain. We first introduce a novel gripper design featuring coupled finger-closing and spine-hooking motions, tightly actuated by a single motor, which achieves exceptional grasping performance (>150 N) despite its lightweight design (525 g). Furthermore, we develop an efficient algorithm to visualize a geometry-based graspability index on continuous rough terrain. Finally, we integrate these components into LIMBERO and demonstrate its ability to ascend steep rocky surfaces under a 1 G gravity condition, a performance not previously achieved yet for limbed climbing robots of this scale.

Abstract

Robot Locomotion

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