Coordinating Spinal and Limb Dynamics for Enhanced Sprawling Robot Mobility

Among vertebrates, salamanders, with their unique ability to transition between walking and swimming gaits, highlight the role of spinal mobility in locomotion. A flexible spine enables undulation of the body through a wavelike motion along the spine, aiding navigation over uneven terrains and obstacles. Yet environmental uncertainties, such as surface irregularities and variations in friction, can significantly disrupt body-limb coordination and cause discrepancies between predictions from mathematical models and real-world outcomes. Addressing this challenge requires the development of sophisticated control strategies capable of dynamically adapting to uncertain conditions while maintaining efficient locomotion. Deep reinforcement learning (DRL) offers a promising framework for handling non-deterministic environments and enabling robotic systems to adapt effectively and perform robustly under challenging conditions. In this study, we comparatively examine learning-based control strategies and biologically inspired gait design methods on a salamander-like robot.

Self-propulsion on spandex: toward a robotic analog gravity system

Numerous laboratory systems have been proposed as analogs to study phenomena (like black holes, Hawking radiation) associated with Einstein's theory of General Relativity (GR) but which are challenging to study in experimental or simulated astrophysical settings. Such analogs, typically acoustic, fluid, or atomic systems require delicate manipulation. Here we introduce a robotic system that captures aspects of Einstein-like dynamics in curved spacetime and creates a path toward a mechatronic analog gravity system. The system consists of a wheeled robotic vehicle transiting a deformable elastic membrane. With a fixed central depression in the membrane (mimicking a massive body), the vehicle paths around the depression resemble the dynamics observed near general-relativistic compact objects (e.g. black holes). We recast the vehicle plus membrane dynamics in physical space into geodesic motion of a so-called "test particle" in a fiducial curved space-time. The mapping facilitates understanding of how vehicle characteristics (e.g. mass) can be modified to change precession dynamics. Since an important aspect of GR is the coupling of matter and spacetime (which influence each other) we also study the dynamics of a two-robot system interacting solely via local membrane deformations. For a range of masses, we observe vehicle "attraction"; initially separated robots converge and collide. A control scheme in which a robot senses its local tilt angle and adjusts its speed enables it to escape capture. Our system provides a path towards a readily tunable analog gravity system and can aid design and control of locomoting devices (e.g. water walkers) that couple strongly to their environments.