Soft Robots Powered By Boiling Water

The soft actuator uses boiling water to move. It works without pumps or high voltage and is used in robots for real-world use.

Researchers at the University of Coimbra have made a new soft actuator that uses boiling water to create movement. It turns water into steam with a small heater inside, which builds pressure and moves soft parts. This method is simple, strong, and easy to scale. It doesn’t need big air pumps, special materials, or high voltage. It can run on just 24 volts, push with over 50 newtons of force, and build pressure quickly at 100 kPa per second.

Why water?

Water was chosen because it is safe, widely available, and works well with heat. Although water needs more energy to vaporise, this trait was shown to help in measuring performance. It also allows for future improvements if safety can be maintained. In testing, the water-based actuators made with silicone moved faster and lasted through over a thousand cycles, showing much better results than older designs.

– Advertisement –

The benefits of modularity

The design focuses on modularity, separating the heating coil, fluid chamber, and outer structure to create a flexible system that works for linear, bending, or mixed motion. The linear actuator uses a McKibben design, and the bending version follows a fast Pneu-Net (fPN) shape. The team used common materials and manufacturing methods like 3d printing and casting. Even though the design is simple, it uses advanced engineering to solve the problem of mechanical vibrations from subcooled boiling using nonlinear control algorithms to keep the boiling stable.

Out in the wild

The team built three simple robots to show what these strong phase-change actuators can do. One is a hand that can move and hold things. Another is a soft gripper that picks up different shapes, like fruit models. The third is a small four-legged robot called Bixo that can climb tubes and crawl on tree trunks. Bixo moves by heating and cooling its parts to grip, pull, and let go. Even though cooling takes time, it can still complete a full movement in about 25 seconds. These robots show a new kind of soft machine that is low-cost, safe, and works well outdoors without needing pumps or harmful materials.

These actuators could be made smaller, stronger, and more efficient in the future. Even now, they give a simple and safe way to build soft robots.