APEX: Learning Adaptive High-Platform Traversal for Humanoid Robots

TL;DR

This paper introduces APEX, a system enabling humanoid robots to traverse high platforms using adaptive, perception-based behaviors trained with a novel reward, achieving robust zero-shot sim-to-real transfer and multi-skill transition.

Contribution

The paper presents APEX, a new approach combining terrain-conditioned behaviors, a generalized ratchet reward, and perception filtering to enable safe, efficient high-platform traversal for humanoid robots.

Findings

Successful zero-shot sim-to-real traversal of 0.8m platforms

Robust adaptation to platform height and initial pose

Smooth multi-skill behavior transitions

Abstract

Humanoid locomotion has advanced rapidly with deep reinforcement learning (DRL), enabling robust feet-based traversal over uneven terrain. Yet platforms beyond leg length remain largely out of reach because current RL training paradigms often converge to jumping-like solutions that are high-impact, torque-limited, and unsafe for real-world deployment. To address this gap, we propose APEX, a system for perceptive, climbing-based high-platform traversal that composes terrain-conditioned behaviors: climb-up and climb-down at vertical edges, walking or crawling on the platform, and stand-up and lie-down for posture reconfiguration. Central to our approach is a generalized ratchet progress reward for learning contact-rich, goal-reaching maneuvers. It tracks the best-so-far task progress and penalizes non-improving steps, providing dense yet velocity-free supervision that enables efficient exploration under strong safety regularization. Based on this formulation, we train LiDAR-based full-body maneuver policies and reduce the sim-to-real perception gap through a dual strategy: modeling mapping artifacts during training and applying filtering and inpainting to elevation maps during deployment. Finally, we distill all six skills into a single policy that autonomously selects behaviors and transitions based on local geometry and commands. Experiments on a 29-DoF Unitree G1 humanoid demonstrate zero-shot sim-to-real traversal of 0.8 meter platforms (approximately 114% of leg length), with robust adaptation to platform height and initial pose, as well as smooth and stable multi-skill transitions.