Background
Soft robotics takes cues from biology to design flexible, adaptable machines that can move through complex environments or handle delicate objects. A key principle in this field is embodied intelligence, where control is physically built into the robot’s structure - often through pneumatic or hydraulic systems - rather than relying on traditional electronics.
These fluidic systems typically require a web of interconnected tubes, valves, sensors, and actuators to pull off even basic tasks. As complexity increases, so does the number of components, resulting in bulky, hard-to-scale designs. While earlier efforts have integrated limited functions like valves with built-in sensors or actuators with embedded switches, a truly unified, reconfigurable component has been missing.
This study addresses that gap with a single, modular fluidic unit that can be tuned to serve as a valve, sensor, or actuator, depending on its configuration. Drawing inspiration from multifunctional biological systems like trunks or tongues, this approach supports more capable robots with less hardware and greater flexibility in design.
Design, Testing, and Performance Evaluation
The unit is made up of four core elements: a 3D-printed body and tube, a flexible sleeve, and a segmented plastic pouch. The parts were created using a Formlabs Form 3B+ SLA printer, with different resins chosen for durability and transparency. After printing, the air channels were carefully cleared to prevent blockages.
The pouch, sourced from a commercial vacuum-sealing bag, was modified with six precisely punched holes (1.3 mm diameter) to regulate airflow. Once folded into a compact zigzag shape and enclosed within the valve body, the pouch completed the fully functional unit.
To test performance, the researchers conducted a range of mechanical and pneumatic experiments. These included:
- Mechanical force testing with an Instron machine to determine how much bending was needed to block airflow
- Pressure monitoring using analog sensors to track how deformation affected flow
- Repeatability tests to ensure consistent behavior, especially for valve functions
- Force output measurements from the inflating pouch under varying pressure levels
For robot motion tracking, the team used a Vicon system with ten Vero cameras to precisely capture movement patterns, including individual limb oscillations.
Findings and Analysis
One of the unit’s most compelling features is its ability to act as a self-oscillating actuator. When configured so the outlet feeds back into the pouch, the unit enters a feedback loop that produces high-frequency oscillations (~31 Hz). Applying an external mechanical counter-force made these oscillations more consistent and increased their range, although it reduced the frequency - a tunable trade-off.
Using these units, the researchers created several soft robots:
- A five-limbed hopper (built on a hollow icosahedron structure) that used self-oscillating actuators. These limbs spontaneously synchronized through physical coupling, resulting in coordinated hopping. The synchronization was accurately modeled using a modified Kuramoto model, which predicted how limb arrangement affected behavior.
- A four-limbed hopper with an asymmetrical layout to break symmetry and achieve forward locomotion. Limbs organized into a “galloping” gait - front and back pairs moved out of phase, driving the robot ahead.
- A boundary-sensing crawler that combined multiple roles in a single system: one unit sensed the edge of a table, another acted as a safety valve, and two others powered locomotion. When the sensor detected a drop-off, it triggered the valve to shut off the actuators, stopping the robot - no electronics required. The behavior was expressed through mechanical logic, essentially: "IF terrain is absent, THEN cut flow to actuators."
Conclusion
This work introduces a modular, multifunctional fluidic unit that dramatically reduces the complexity of soft robot design by integrating the roles of valve, sensor, and actuator into a single component. By building autonomous robots that can move, sense, and respond without any electronics, the research opens new paths for truly self-contained soft machines.
While the mechanics of the unit are largely scale-independent, the researchers note that at smaller sizes, fluid dynamics become dominated by viscosity, which poses challenges for micro-scale applications. Future directions include exploring monolithic fabrication to reduce assembly steps and developing software tools to make design and integration more intuitive.
Journal Reference
Mousa, M., Comoretto, A., Overvelde, J. T., & Forte, A. E. (2025). Multifunctional fluidic units for emergent, responsive robotic behaviors. Advanced Materials, e10298. DOI:10.1002/adma.202510298. https://advanced.onlinelibrary.wiley.com/doi/10.1002/adma.202510298
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