A Novel Multi-Gait Strategy for Stable and Efficient Quadruped Robot Locomotion

TL;DR

The paper addresses the challenge of achieving energy-efficient and stable locomotion for quadruped robots across diverse terrains and speeds. It introduces a two-part framework: (i) a gait-transition mechanism that uses affine transformations of gait parameters together with a finite-state machine to switch among five gaits, and (ii) a gait-map that selects gaits by minimizing a combined index $J_e(\boldsymbol{\Lambda}) = c \cdot STB + (1-c) \cdot CoT$, where $CoT = W/(m g \Delta s)$ and $STB$ encodes body stability. Five gaits are defined via duty factor $\beta$ and leg-phase offsets $\boldsymbol{\phi}$, and the map is built from extensive experiments to capture velocity and terrain effects, enabling terrain- and speed-aware gait selection. Experiments demonstrate smoother transitions, a velocity-to-gait map on flat and slope terrains, and real-world validation on a Unitree Go2, showing the approach can deliver stable and energy-efficient locomotion with real-time gait switching under varied conditions.

Abstract

Taking inspiration from the natural gait transition mechanism of quadrupeds, devising a good gait transition strategy is important for quadruped robots to achieve energy-efficient locomotion on various terrains and velocities. While previous studies have recognized that gait patterns linked to velocities impact two key factors, the Cost of Transport (CoT) and the stability of robot locomotion, only a limited number of studies have effectively combined these factors to design a mechanism that ensures both efficiency and stability in quadruped robot locomotion. In this paper, we propose a multi-gait selection and transition strategy to achieve stable and efficient locomotion across different terrains. Our strategy starts by establishing a gait mapping considering both CoT and locomotion stability to guide the gait selection process during locomotion. Then, we achieve gait switching in time by introducing affine transformations for gait parameters and a designed finite state machine to build the switching order. Comprehensive experiments have been conducted on using our strategy with changing terrains and velocities, and the results indicate that our proposed strategy outperforms baseline methods in achieving simultaneous efficiency in locomotion by considering CoT and stability.

Figures (9)

• Figure 1: Illustration of the proposed strategy to achieve gait selecting and switching of quadruped robots. (A) shows the goal and working environment of a quadruped robot with different terrains. (B) shows the multi-gait strategy, including a gait transition between five gait patterns and a gait selection on two different terrains; the same color of feet represents the related legs swing simultaneously.
• Figure 2: A phase diagram of five classical gait patterns for a quadruped robot. The black blocks represent the stance phase, while the blank ones represent the swing phase for each leg. T represents one stride period.
• Figure 3: The graph for switching between gait patterns. $a_{ij}$ represents the switching action from state $i$ to state $j$.
• Figure 4: The feet's height variation in transition processes. The upper plot of each subfigure shows the roll and pitch angle of the robot's body, while the bottom one shows the feet's position in the z-direction, and the yellow parts represent the transition process.
• Figure 5: The index value of different gait patterns on two terrains.