Designing for Compliance: ESCHER, Team VALOR’s Compliant Biped

Submitted to Journal of Field Robotics
Contributing Author: Brian Lattimer, JENSEN HUGHES Director


This paper presents the hardware platform, software, and control systems developed to field the Electric Series Compliant Humanoid for Emergency Response (ESCHER), Team VALOR’s Track A entry to the DARPA Robotics Challenge (DRC) Finals. The design and assembly of ESCHER commenced 10 months prior to the Finals, leveraging and improving upon bipedal humanoid tech-nologies implemented in previous research efforts. ESCHER’s unique features include custom lin-ear series elastic actuators (SEAs), a dual-axis motor controller enabling high-bandwidth impedance control of parallelly actuated joints, and a whole-body control framework supporting compliant lo-comotion across variable and shifting terrain. Additionally, a high-level software system designed using Robot Operating System (ROS) interfaced with the existing whole-body motion controller and integrated various open-source packages. Empirical data collected before, during, and after the DRC Finals validate ESCHER’s performance in fielded environments. The paper discusses a de-tailed analysis of challenges encountered during the competition, along with lessons learned critical for transitioning research contributions to a fielded robot. The compliant lower body proved crucial for reliable traversal across the 61 m loose dirt course at the Finals, as well as extending compliance to the rigid upper body for safe interaction with the environment.

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