Brushing Up on Active Matter Research

There is a lot of excitement in the world of robotics about swarms of machines that can self-organize to carry out complex tasks. If large schools of fish and swarms of insects can do it, then why not robots? But programming large numbers of robots to interact with one another in close proximity, without crashing into one another and doing more harm than good, is fraught with difficulty. Traditional control systems are not only too expensive to deploy in these scenarios, but coordinating all of them is much too complicated.

These factors have led researchers in the area to explore the field of active matter studies. This field seeks to understand how large numbers of individual agents can give rise to complex behaviors through simple interactions. Large numbers of robots are required in these studies, so simplicity is the name of the game. Bristlebots, which vibrate and move around on toothbrush-like bristles (think Hexbugs), are particularly popular for this reason.

However, for many areas of research, these robots are just too simple. To understand interactions between robots, for instance, they need to be equipped with a variety of sensors. So to fill this gap, while maintaining viability for active matter studies, a team led by researchers at the University of Liège developed GRASPion. It is an open source, Arduino-compatible bristlebot loaded with sensors and wireless communications equipment.

The robot’s body is 3D-printed from ABS plastic in an ellipsoidal shape measuring about 60 millimeters long, 30 millimeters wide, and just 9 millimeters tall (excluding the legs). This streamlined form keeps the total weight down to around six grams while maintaining structural integrity.

The robot “walks” on four 3D-printed legs that are mounted at a slight angle to the vertical. These legs are attached as a removable leg plate secured with screws, making replacements straightforward in case of wear or breakage. A small wedge sits between the leg plate and the body, tilting the robot forward and helping it achieve more consistent motion. Different leg designs are available depending on whether precision or durability is the priority, and these subtle design choices allow the GRASPion to reliably produce controlled trajectories.

Propulsion comes from two independent vibrating motors mounted inside the body. By adjusting the voltage and polarity applied to each motor through the onboard firmware, GRASPion can move forward, turn, or even exhibit randomized, diffusive motion.

Built around an Adafruit QtPy SAMD21 board, powered by an Arm Cortex M0+ processor, the system provides both affordability and accessibility through the Arduino ecosystem. A secondary AVR coprocessor handles lower-level tasks such as charging and infrared communication. This separation allows researchers to program higher-level behaviors through the familiar Arduino IDE without worrying about hardware management.

Onboard hardware includes an IR transmitter and receiver for communication between robots, a three-axis magnetometer, two programmable RGB LEDs, onboard flash memory, and an ambient light sensor. A modular front-facing add-on currently houses a proximity detector, a color sensor, and a gesture sensor, but the design leaves room for expansion.

With a runtime of over 90 minutes, swarms of these small robots can be deployed in classrooms or laboratories for long, continuous experiments. And unlike some previous research platforms, GRASPion is available not just as a set of design files but also as a ready-to-use commercial product, lowering the barrier to entry for educators and researchers alike.