Tactile sensing enables vertical obstacle negotiation for elongate many-legged robots

TL;DR

This work addresses the challenge of enabling 3D vertical climbing for mid-sized elongated many-legged robots operating in confined and rugged environments. It introduces a tactile sensing framework combining a tactile antenna for short-range obstacle probing with binary foot-contact sensing, paired with a two-phase feedback controller that independently regulates the head and subsequent segments to negotiate obstacles. The approach achieves reliable climbing up to $5$ times the center height and remains robust when facing shifting debris, rapid curvature changes, and outdoor conditions such as pipe interiors, demonstrating practical potential for inspection and search tasks in complex terrains. By avoiding heavy vision-based perception and leveraging simple, low-bandwidth tactile sensing, this method offers a scalable path toward low-profile, highly capable many-legged robots for real-world 3D locomotion and exploration.

Abstract

Many-legged elongated robots show promise for reliable mobility on rugged landscapes. However, most studies on these systems focus on planar motion planning without addressing rapid vertical motion. Despite their success on mild rugged terrains, recent field tests reveal a critical need for 3D behaviors (e.g., climbing or traversing tall obstacles). The challenges of 3D motion planning partially lie in designing sensing and control for a complex high-degree-of-freedom system, typically with over 25 degrees of freedom. To address the first challenge regarding sensing, we propose a tactile antenna system that enables the robot to probe obstacles to gather information about their structure. Building on this sensory input, we develop a control framework that integrates data from the antenna and foot contact sensors to dynamically adjust the robot's vertical body undulation for effective climbing. With the addition of simple, low-bandwidth tactile sensors, a robot with high static stability and redundancy exhibits predictable climbing performance in complex environments using a simple feedback controller. Laboratory and outdoor experiments demonstrate the robot's ability to climb obstacles up to five times its height. Moreover, the robot exhibits robust climbing capabilities on obstacles covered with shifting, robot-sized random items and those characterized by rapidly changing curvatures. These findings demonstrate an alternative solution to perceive the environment and facilitate effective response for legged robots, paving ways towards future highly capable, low-profile many-legged robots.

Figures (13)

• Figure 1: Tacitly sensing multilegged robot climbing in different environments. (Top) The robot climbs a large rock, four times its height, in a confined space with terrain covered in mud, grass, and scattered boulders. (Middle) The robot successfully navigates confined environments with vertical obstacles, unstable metal bars, and flowable plastic disks. (Bottom) The robot climbs obstacles five times its height with rapidly changing curvatures in a laboratory setting.
• Figure 2: Robot wave templates: A. Overhead view of the robot: $\theta_{leg}$ (shoulder angle) and $\theta_{body}$ (horizontal body joint angle) are determined by leg amplitude $\Theta_{leg}$ and body amplitude $\Theta_{body}$, respectively. B. Side view of the robot: $\theta_v$ (vertical body joint angle) is determined by vertical amplitude $A_v$.
• Figure 3: Tactile sensory system.A. Antenna design. A1. The base of the antenna is attached to a Force Resistive Sensor (FSR) using screws. The inner part of the antenna is connected to its tip with two springs, allowing it to deform upon contact with obstacles, thereby preventing jamming. A2. Antenna contact states: A value of 0 represents no contact (void state), while 1 indicates an obstacle has been detected. B. Binary limb contact sensing system. B1. Design of a binary contact sensor for each foot, based on capacitive sensing. B2. Contact state of the leg: 0 indicates no contact, while 1 indicates contact.
• Figure 4: Open loop experiments. A. Forward/vertical displacement vs. time plot showing the robot climbing 5 cm and 10 cm obstacles without vertical body undulation. The inset illustrates how the robot becomes blocked without the use of vertical waves. B. A forward/vertical displacement vs. time plot showing the robot climbing 5 cm and 10 cm obstacles with vertical body undulation. The inset demonstrates how introducing vertical body undulation raises the robot's belly height, increasing its maximum climbing capability.
• Figure 5: Obstacle height estimation. The z-position of the antenna tip relative to the head joint can be estimated using a rigid transformation, based on the length of the head segment ($L_1$) and the antenna ($L_a$), along with the joint angle history.