On State Estimation for Legged Locomotion over Soft Terrain

TL;DR

This paper investigates how soft terrain impacts state estimation in legged robots, revealing that soft terrain causes increased drift in estimates when using estimators designed for rigid contacts.

Contribution

It highlights the limitations of existing state estimators on soft terrain and provides experimental validation of the drift issue using the HyQ robot.

Findings

Soft terrain causes increased drift in state estimates.

Existing estimators designed for rigid contact are less accurate on soft terrain.

Experimental validation shows significant differences in estimation accuracy between terrains.

Abstract

Locomotion over soft terrain remains a challenging problem for legged robots. Most of the work done on state estimation for legged robots is designed for rigid contacts, and does not take into account the physical parameters of the terrain. That said, this letter answers the following questions: how and why does soft terrain affect state estimation for legged robots? To do so, we utilized a state estimator that fuses IMU measurements with leg odometry that is designed with rigid contact assumptions. We experimentally validated the state estimator with the HyQ robot trotting over both soft and rigid terrain. We demonstrate that soft terrain negatively affects state estimation for legged robots, and that the state estimates have a noticeable drift over soft terrain compared to rigid terrain.