An Agnostic End-Effector Alignment Controller for Robust Assembly of Modular Space Robots

TL;DR

This paper presents a novel, hardware-agnostic end-effector alignment controller for modular space robots that adaptively manages velocity bounds to ensure smooth, stable, and accurate assembly in lunar environments.

Contribution

It introduces a new adaptive velocity bounding controller using a dynamic hypersphere clamp, tested on MoonBot limbs, enhancing robustness and reconfigurability for lunar robotic assembly.

Findings

Step-based variant yields predictable, low-wobble motions.

Continuous variant converges faster with millimeter accuracy.

Both variants are robust to mechanical imperfections and noise.

Abstract

Modular robots offer reconfigurability and fault tolerance essential for lunar missions, but require controllers that adapt safely to real-world disturbances. We build on our previous hardware-agnostic actuator synchronization in Motion Stack to develop a new controller enforcing adaptive velocity bounds via a dynamic hypersphere clamp. Using only real-time end-effector and target pose measurements, the controller adjusts its translational and rotational speed limits to ensure smooth, stable alignment without abrupt motions. We implemented two variants, a discrete, step-based version and a continuous, velocity-based version, and tested them on two MoonBot limbs in JAXA's lunar environment simulator. Field trials demonstrate that the step-based variant produces highly predictable, low-wobble motions, while the continuous variant converges more quickly and maintains millimeter-level positional accuracy, and both remain robust across limbs with differing mechanical imperfections and sensing noise (e.g., backlash and flex). These results highlight the flexibility and robustness of our robot-agnostic framework for autonomous self-assembly and reconfiguration under harsh conditions.