School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Department of Mechanical Engineering, California State University, Los Angeles, CA 90032, USA.
Phys Rev E. 2019 Feb;99(2-1):022606. doi: 10.1103/PhysRevE.99.022606.
Natural and artificial self-propelled systems must manage environmental interactions during movement. In complex environments, these interactions include active collisions, in which propulsive forces create persistent contacts with heterogeneities. Due to the driven and dissipative nature of these systems, such collisions are fundamentally different from those typically studied in classical physics. Here we experimentally and numerically study the effects of active collisions on a laterally undulating sensory-deprived robophysical model, whose dynamics are relevant to self-propelled systems across length scales and environments. Interactions with a single rigid post scatter the robot, and this deflection is dominated by head-post contact. These results motivate a model which reduces the snake to a circular particle with two key features: The collision dynamics are set by internal driving subject to the geometric constraints of the post, and the particle has an effective length equal to the wavelength of the snake. Interactions with a single row of evenly spaced posts (with interpost spacing d) produce distributions reminiscent of far-field diffraction patterns: As d decreases, distinct secondary peaks emerge as large deflections become more likely. Surprisingly, we find that the presence of multiple posts does not change the nature of individual collisions; instead, multimodal scattering patterns arise from multiple posts altering the likelihood of individual collisions to occur. As d decreases, collisions near the leading edges of the posts become more probable, and we find that these interactions are associated with larger deflections. Our results, which highlight the surprising dynamics that can occur during active collisions of self-propelled systems, can inform control principles for locomotors in complex terrain and facilitate design of task-capable active matter.
自然和人工自主推进系统在运动过程中必须管理环境相互作用。在复杂的环境中，这些相互作用包括主动碰撞，其中推进力与非均匀性产生持久接触。由于这些系统的驱动和耗散性质，这种碰撞与经典物理学中通常研究的碰撞有根本的不同。在这里，我们通过实验和数值研究了主动碰撞对侧向波动的感觉剥夺 robophysical 模型的影响，其动力学与跨越长度尺度和环境的自主推进系统有关。与单个刚性柱的相互作用会使机器人发生散射，而这种偏转主要由头部与柱的接触决定。这些结果促使我们提出了一个模型，将蛇简化为一个具有两个关键特征的圆形粒子：碰撞动力学由内部驱动力决定，同时受到柱的几何约束，粒子的有效长度等于蛇的波长。与单排均匀间隔的柱子（柱间距为 d）相互作用会产生类似于远场衍射模式的分布：随着 d 的减小，大的偏转变得更有可能，因此会出现明显的二次峰。令人惊讶的是，我们发现多个柱子的存在不会改变单个碰撞的性质；相反，多峰散射模式是由多个柱子改变单个碰撞发生的可能性引起的。随着 d 的减小，柱子前缘附近的碰撞变得更加可能，我们发现这些相互作用与更大的偏转有关。我们的结果强调了自主推进系统在主动碰撞过程中可能出现的惊人动力学，这可以为复杂地形中的运动器提供控制原理，并有助于设计具有任务能力的主动物质。
