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. · The author is with the National Institute of Applied Sciences of Toulouse, 31400 Toulouse, France.
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.
Figures & tables
Fig. 1: LIMBERO: A Limbed Climbing Exploration Robot. LIMBERO’s spine gripper can hold 15 kg load in Earth gravity (bottom left). Developed algorithm can visualize graspability score in the irregular terrain map (bottom right).
Robot
Mass
Num. of
Active DOF
Gripper
Grasping Force
Terrain
Gravity
Limbs
per Limb
Actuation
Gripping Principle ‡1
per Gripper
LEMUR 3 [ 12 ]
35 kg
4
7
Active
Radial hooking
150 N
Rocky terrain
3/8 G
ReachBot [ 4 ]
18 kg
8
3
Active
Radial biting and hooking
22 N ‡2
Rocky terrain
3/8 G
LIMBERO
9.7 kg
4
4
Active
Radial biting and hooking
150 N
Rocky terrain
1 G
SCALER [ 18 ]
9.6 kg
4
6
Active
Two-fingered biting
> 30 N ‡2
Artificial holds
1 G
MARCBot [ 27 ]
4.8 kg
4
5
Active
Radial biting and hooking
49.0 N
Rocky terrain
1 G
TABLE I: Comparative summary of the state-of-the-art limbed climbing robots (ordered by weight).
Fig. 2: Grasping performance by the developed gripper.
Fig. 3: Gripper design: a servo motor drives a worm and two worm wheels, which linearly move the stage (yellow) to tighten or loosen the metal wires, thereby opening and closing the gripper.
Fig. 4: Limb design: three actuators are concentrated at the shoulder via a parallel-linked mechanism, reducing limb inertia while preserving a large workspace. Three pitch joints requiring high torque capacity are equipped with a 3.5:1 planetary gear reduction.
Fig. 5: Base design: an axisymmetric structure accomodates electronics, sensors, and batteries.
Fig. 6: Software architecture implemented for LIMBERO.
Fig. 7: Case study of the gripper mask matching method over various terrain. The terrain array and the gripper mask are illustrated in simplified cross-sectional view.
Fig. 8: The output of the graspability is an interpolated point cloud, with colors representing the graspability score of each point. Higher-resolution settings for voxelization require longer computation time, but achieve more accurate scoring (right).
Fig. 9: Cliff holding test by LIMBERO. The robot demonstrated 1.4 kg payload capacity under Earth gravity.
Fig. 10: Rock climbing with LIMBERO under full Earth gravity. The right foothold history indicates the initial grasping points (black dots) and the step order (numbers) on the graspability-assessed terrain map. The 7th step represents a regrasping action around the same foothold. Regions with very low graspability are omitted from the visualization.
Fig. 11: Power consumption of all actuators of LIMBERO during climbing. Several peaks correspond to periods when the robot pushes the base upward.
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
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.
Keita Nagaoka, Kentaro Uno, Kazuya Yoshida
The authors are with the Space Robotics Lab. (SRL) in Department of Aerospace Engineering, Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan.
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.