Robust and Modular Multi-Limb Synchronization in Motion Stack for Space Robots with Trajectory Clamping via Hypersphere

TL;DR

The paper addresses the challenge of synchronizing trajectories across heterogeneous, modular space robots under significant disturbances and limited system knowledge. It introduces a hypersphere-based trajectory clamping mechanism within a system-agnostic framework and implements both single and multi-end-effector variants as part of the open-source Motion Stack API. Key contributions include an adaptive, real-time clamping strategy that preserves the intended path, robust recovery from disconnections and power loss, and validation on six diverse limbs. This approach offers a flexible, safer alternative to planning-heavy methods for coordinating modular space robots and supports rapid prototyping in extreme environments.

Abstract

Modular robotics holds immense potential for space exploration, where reliability, repairability, and reusability are critical for cost-effective missions. Coordination between heterogeneous units is paramount for precision tasks -- whether in manipulation, legged locomotion, or multi-robot interaction. Such modular systems introduce challenges far exceeding those in monolithic robot architectures. This study presents a robust method for synchronizing the trajectories of multiple heterogeneous actuators, adapting dynamically to system variations with minimal system knowledge. This design makes it inherently robot-agnostic, thus highly suited for modularity. To ensure smooth trajectory adherence, the multidimensional state is constrained within a hypersphere representing the allowable deviation. The distance metric can be adapted hence, depending on the task and system under control, deformation of the constraint region is possible. This approach is compatible with a wide range of robotic platforms and serves as a core interface for Motion-Stack, our new open-source universal framework for limb coordination (available at https://github.com/2lian/Motion-Stack ). The method is validated by synchronizing the end-effectors of six highly heterogeneous robotic limbs, evaluating both trajectory adherence and recovery from significant external disturbances.

Figures (6)

• Figure 1: Six heterogeneous limbs Synchronously performing a trajectory. Blue: Heavy limb; Green: Quadruped; Red: Light limb.
• Figure 2: Trajectory of the limbs \ref{['fig:overview']}, being purposefully disrupted during the 12-minute robustness experiment.
• Figure 3: Snapshots of the heavy limb safely pausing a trajectory partially outside its range of motion.
• Figure 4: Heavy limb driven outside its range of motion, by a pure $z$ speed trajectory. Clamping pauses the impossible movement, thus preserving the trajectory's path.
• Figure 5: Four corners of the square trajectory, synchronously performed by Heavy limb (Blue), Quadruped (Green), and Light limb (Red).