GRASPion: An open-source, programmable brainbot for active matter research.

We present the GRASPion, a compact, open-source bristlebot designed for the controlled study of active matter systems. Built around an Arduino-compatible board and modular 3D-printed components, the GRASPion combines ease of use, programmability, and mechanical versatility. It features dual vibrating motors for self-propulsion, integrated sensors for local interaction, and customizable firmware enabling various motion modes, from ballistic to diffusive regimes. The robot is equipped with onboard IR communication, color and proximity sensors, and a magnetometer, allowing for real-time interaction and complex collective behaviors. With a runtime exceeding 90 min and reproducible fabrication, the GRASPion provides a robust and scalable platform for both educational and research applications in out-of-equilibrium physics. This article details the mechanical and electronic design and software architecture of the GRASPion and illustrates its capabilities through prototypical experiments relevant to active matter, such as diffusive motion, synchronization, and phototaxis.