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.
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 ϕ .
Fig. 4: Holding force measurement setup. The pin-array gripper’s engaging performance was tested on various convex and concave objects with different Φ=±30∘,±60∘,±90∘ , 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 ±5∘ in roll and pitch), owing to its highly terrain-adaptive locomotion.
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.
Kentaro Uno, Masazumi Imai, Kazuki Takada +7
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.
Animals such as squirrels and even bears have adapted to rapidly climb up trees and other complex vertical terrain, but achieving comparable agility has been a challenge for climbing robots. Existing robots often use walking gaits and move conservatively to stay in contact with the surface, which limits the range of dynamic maneuvers. In this paper we present a 290 g robot that, to our knowledge, is the first to climb vertically by bounding (with an aerial phase). We leverage a co-design workflow, in which the morphology and trajectory are jointly optimized for fast locomotion, subject to adhesion force limitations seen in spined grippers. The resulting trajectory includes a rapid maneuver that launches the robot vertically, and an aerial reorientation that brings the front grippers back to the surface using the rear leg as an inertial tail. We evaluate the resulting jump forces in 2D force space and demonstrate that the optimized morphology is capable of continuous climbing at a speed of 0.375 m/s (1.97 body lengths/s), and can also achieve ground locomotion and transition to a vertical surface. Our work proposes design insights for the jump-climbing maneuver and serves as an important step toward creating climbing robots with agility on par with that of animals.
Christopher Y. Xu, Elliot W. Hawkes
Department of Mechanical Engineering at the University of California Santa Barbara.
This paper presents an open-sourced MATLAB simulation and analysis platform dedicated to legged climbing robots. This simulator enables the design of any limbed robotic system as an articulated multi-body with a floating base and simulates it walking and climbing in an arbitrary environment. The main variable environmental parameters are inclination, gravity, and ground stiffness, and any point cloud can be installed as the terrain map. Furthermore, the simulator employs a rigid body dynamics engine. This paper first describes the simulator structure, and the computational flow and next presents the representative simulation examples where quadrupedal robots assumed gripping on the wall or climbing on the steep slope.
Kentaro Uno, Warley F. R. Ribeiro, Yusuke Koizumi +4
Space Robotics Lab (SRL), Department of Aerospace Engineering, Tohoku University, Aoba 6-6-01, Aramaki-Aza, Aoba-ku, Sendai, Miyagi 980-8579, Japan · VisionSpace Technologies GmbH, Robert-Bosch Straße 7, 64293 Darmstadt, Germany