However, unlike the cuboidal robot, the cuboidal animal was capable of escaping obstacle attraction and subsequent high pitching and flipping over, which inspired us to develop an empirical pitch-and-turn strategy for cuboidal robots. The animal displayed qualitatively similar turning and pitching motions induced by these two body shapes. By contrast, with an elliptical body, the robot was repelled by obstacles and readily traversed. With a common cuboidal body, the robot was attracted towards obstacles, resulting in pitching up and flipping-over.
Here, inspired by recent discovery of a terradynamic streamlined shape, we studied how two body shapes interacting with obstacles affect turning and pitching motions of an open-loop multi-legged robot and cockroaches during dynamic locomotion. Body–obstacle interaction is often inevitable and induces perturbation and uncertainty in motion that challenges closed-form dynamic modeling. Robots still struggle to dynamically traverse complex 3D terrain with many large obstacles, an ability required for many critical applications. Vertical undulations can provide snakes a valuable locomotor tool for taking advantage of vertical asperities in a variety of habitats, potentially in combination with lateral undulation, to fully exploit the 3D structure of the habitat. Additional tests showed that snakes could propel themselves via vertical undulations from a single suitable contact point, and this mechanism was replicated in a robotic model. Using an array of horizontally oriented cylinders, one of which was equipped with force sensors, and a motion capture system, we found snakes generated substantial propulsive force and propulsive impulse with minimal contribution from lateral undulation. We hypothesized that snakes can generate propulsion using a similar mechanism of posteriorly propagating vertical waves pressing against suitably oriented environmental asperities. grass, rocks) and generate propulsive reaction forces. Lateral undulation is the most widespread mode of terrestrial vertebrate limbless locomotion, in which posteriorly propagating horizontal waves press against environmental asperities (e.g.
We also identified issues that needs improvement in further development. In general, sensory feedback helps better maintain or regain contact and propulsion, but different types of feedback displayed different tradeoffs and varied performance. Feedforward propagation of vertical bending that conforms to the terrain a priori can produce propulsion but fails with terrain perturbation that breaks conformation. We tested the robot using vertical bending to traverse a large obstacle and compared five controllers without and with various sensory feedback using various force and torque information, as well as various load and terrain conditions to perturb the system. Here, we explore this question by testing a previously developed robot with contact forces sensors added. Although snake robots can propagate a vertical bending shape to passively push to traverse such terrain, it is possible that active pushing modulated by contact force and internal torque sensing can further help control propulsion.
Recent animal experiments revealed that vertical bending is also important for generating propulsion during traversal of terrain with large height variation. Previous snake robots often used lateral bending to push against vertical structures on flat surfaces. Snake robots hold the promise as a versatile platform to traverse complex environments.
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