Dynamic Walking on Slippery Surfaces : Demonstrating Stable Bipedal Gaits with Planned Ground Slippage

Abstract

Dynamic bipedal robot locomotion has achieved remarkable success due in part to recent advances in trajectory generation and nonlinear control for stabilization. A key assumption utilized in both theory and experiments is that the robot's stance foot always makes no-slip contact with the ground, including at impacts. This assumption breaks down on slippery low-friction surfaces, as commonly encountered in outdoor terrains, leading to failure and loss of stability. In this work, we extend the theoretical analysis and trajectory optimization to account for stick-slip transitions at point foot contact using Coulomb's friction law. Using AMBER-3M planar biped robot as an experimental platform, we demonstrate for the first time a slippery walking gait which can be stabilized successfully both on a lubricated surface and on a rough no-slip surface. We also study the influence of foot slippage on reducing the mechanical cost of transport, and compare energy efficiency in both numerical simulations and experimental measurements.

Dynamic Walking: Toward Agile and Efficient Bipedal Robots

“…In real life, impacts are not truly instantaneous and do not always achieve stiction (89). Situations with multiple impacts can arise (90) leading to Zeno behaviors (91,92,93), or slippage (94,95).…”

Preference-Based Learning for User-Guided HZD Gait Generation on Bipedal Walking Robots

“…This custom research platform has three interchangeable lower-limb configurations (flat-foot, point-foot, and spring-foot) and was originally built to study how leg configurations effect energy efficiency. We specifically selected this platform because of its engineering reliability [12], enabling consistent data collection to isolate the effects of various gaits in the learning process. The controller for AMBER-3M is implemented on an off-board i7-6700HQ CPU @ 2.6GHz with 16 GB RAM, which computes desired torques and communicates them with the ELMO motor drivers.…”

“…This is accomplished by characterizing walking with hybrid systems that encode state jumps and Lyapunov methods robust to these jumps [7]- [9]. This approach has been demonstrated for walking [10], running [11], and quadrupedal locomotion [12]. To achieve experimental success, however, one needs more than the theoretic stability This research was supported by NSF NRI award 1924526 and CMMI award 1923239, NSF Graduate Research Fellowship No.…”

Footstep Adjustment for Biped Push Recovery on Slippery Surfaces

“…Moreover, this controller has an analytical form, consisting of some simple closed-form solutions for computing the control inputs, in contrast to the non-deterministic optimization methods existing in the literature [16], which nevertheless also employed simplified dynamics models of the biped. On the other side, the main focus of studies on biped walking on slippery surfaces is gait generation in the absence of external disturbances [19,20,21,22,23,24]. The proposed stabilizer here complements those planners by stabilizing generated gaits in the confrontation of external disturbances.…”

“…The risk of slippage can be reduced by defining a gait-planning optimization problem that minimizes the horizontal acceleration of the center of mass (CoM) as a part of its objective [21]. By extending gait planning optimization problems to account for stick-slip transitions, pre-planned gaits which incorporate slippage can be generated to provide stable walking on low-friction surfaces [22]. Using reflex strategies such as lifting the hip for the immediate modification of ground reaction forces [23] is another way used for slippage recovery on low-friction surfaces.…”