Soft machines and robots are becoming more and more functional, capable of moving, jumping, gripping an object, and even changing color. The elements responsible for their actuation motion are often soft, inflatable segments called fluidic actuators. These actuators require large amounts of air or water to change shape, making the machines slow, bulky and difficult to untether. Harvard researchers engineered a new, soft actuator that harnesses the power of instability to trigger instantaneous movement.

New soft actuators harness the power of instability to trigger instantaneous movement. (Bertoldi Group)

The actuator is inspired by a physics experiment in which two balloons are inflated to different sizes and connected via a tube and valve. When the valve is opened, air flows between the balloons. Instead of equalizing in size, as one might expect, the larger balloon inflates more while the smaller balloon deflates.

The researchers connected fluidic segments in such a way that an interplay between their non-linear response results in unexpected behavior. Certain combinations of these interconnected segments can result in fast-moving instabilities with negligible change in volume. If harnessed, these instabilities would allow soft robots to move quickly without needing to carry or be tethered to a fluid supply.