Lateral Oscillation and Body Compliance Help Snakes and Snake Robots Stably Traverse Large, Smooth Obstacles

Abstract

SynopsisSnakes can move through almost any terrain. Similarly, snake robots hold the promise as a versatile platform to traverse complex environments like earthquake rubble. Unlike snake locomotion on flat surfaces which is inherently stable, when snakes traverse complex terrain by deforming their body out of plane, it becomes challenging to maintain stability. Here, we review our recent progress in understanding how snakes and snake robots traverse large, smooth obstacles like boulders and felled trees that lack "anchor points" for gripping or bracing. First, we discovered that the generalist variable kingsnake combines lateral oscillation and cantilevering. Regardless of step height and surface friction, the overall gait is preserved. Next, to quantify static stability of the snake, we developed a method to interpolate continuous body in three dimensions (both position and orientation) between discrete tracked markers. By analyzing the base of support using the interpolated continuous body 3-D kinematics, we discovered that the snake maintained perfect stability during traversal, even on the most challenging low friction, high step. Finally, we applied this gait to a snake robot and systematically tested its performance traversing large steps with variable heights to further understand stability principles. The robot rapidly and stably traversed steps nearly as high as a third of its body length. As step height increased, the robot rolled more frequently to the extent of flipping over, reducing traversal probability. The absence of such failure in the snake with a compliant body inspired us to add body compliance to the robot. With better surface contact, the compliant body robot suffered less roll instability and traversed high steps atIntegrative and Comparative Biology (2020), icaa013, https://doi.org/10.1093/icb/icaa013; https://li.me.jhu.edu/ 2 higher probability, without sacrificing traversal speed. Our robot traversed large step-like obstacles more rapidly than most previous snake robots, approaching that of the animal. The combination of lateral oscillation and body compliance to form a large, reliable base of support may be useful for snakes and snake robots to traverse diverse 3-D environments with large, smooth obstacles.

A Survey on Snake Robot Locomotion

“…Lateral oscillations and body compliance help snake robots achieve stable traversal [55]. Where α is the amplitude of oscillation, ω is the frequency, δ is the phase shift between joints, and ϕ0 is the joint offset which depends on the direction of locomotion.…”

“…Furthermore, the method considers the snake robot's velocity and acceleration limitation when following the created route. [55], [59] created a snake robot with lateral undulation, cantilever gait, and snake-like anisotropic friction that can climb stairs up to one-third of its body length fast and steadily. When ascending a short route, snake robot modules can use friction to sustain the robot's whole weight if both modules' ends exert adequate pressure on the passage wall.…”

Dynamic Modeling of Underwater Snake Robot by Hybrid Rigid-Soft Actuation

“…Hence, the three-dimensional modeling of an underwater robotic snake will facilitate the understanding of motions in swimming and the design of motion controllers. Several groups have preliminarily studied the three-dimensional modeling of the robotic snake in the literature [31][32][33]. However, these models are typically incomplete in predicting multimodal three-dimensional behaviors.…”

Locomotor transitions in the potential energy landscape-dominated regime

“…Here, we review our approaches, progress and opportunities ahead. This review focuses on multi-legged locomotor transitions; for our work on limbless locomotion in three-dimensional terrain, see [42][43][44][45][46][47]. We studied the rainforest-dwelling discoid cockroach (figure 3a), which is exceptional at traversing complex threedimensional terrain with diverse large obstacles such as vegetation, foliage, crevices and rocks [4].…”