These Soft Robots Go with the Flow

In many ways, robots are a cheap knock off of biological organisms. They are often designed to mimic the capabilities of humans, dogs, or other living beings, but they operate in a much more simplistic way. You will find, for example, that functions are split up into discrete subsystems — actuation, structural support, power delivery, and so on. Each of these functions operates more or less independently of the others. Yet in the natural world, these functions are far more tightly integrated with one another — and that results in efficiencies that engineers cannot match with traditional approaches.

Cornell University researchers are attempting to move beyond this traditional approach by developing robots that integrate energy storage directly into their structure, a strategy called "embodied energy." This innovation, inspired by nature, reduces robot weight and increases efficiency. Two creations from Cornell’s Organic Robotics Lab and Archer Group exemplify this approach: a jellyfish-inspired underwater robot and a modular worm robot designed for use on land.

The jellyfish robot features a redox flow battery (RFB) integrated into its body that has been likened to a "robot blood." The RFB uses electrolytic fluids to store and release energy through chemical reduction and oxidation reactions. A tendon within the battery contracts and relaxes to alter the shape of the robot’s bell, propelling it upward through water. When the bell relaxes, the robot sinks back down, mimicking the swimming motion of a real jellyfish. Innovations such as graphene coatings that prevent zinc dendrite buildup on the battery’s electrical substrates, as well as the addition of bromine to improve ion transport, have significantly increased the battery’s capacity and power density. This lightweight, efficient design allows the jellyfish to travel for longer durations than other robots, making it an ideal candidate for consideration in future ocean explorations.

Unlike aquatic robots, which benefit from buoyancy, the worm robot must rely on the ground for support. It is composed of a modular series of interconnected pods, each containing its own motor, tendon actuator, and battery compartments. The pods are designed to work in unison, enabling the worm’s body to compress and expand as it crawls forward or climbs vertically. This mimics the motion and adaptability of simple land organisms, such as caterpillars or inchworms.

Key to the worm’s design is a compartmentalized battery system, which was constructed using a unique fabrication method. During production, researchers bonded Nafion battery separators directly to the robot’s silicone-urethane body using a dry-adhesion technique. This ensures efficient energy transfer while reducing the robot’s weight. Additionally, the hydraulic fluid powering the robot also serves as the battery, performing dual functions to further optimize efficiency. Although the worm’s speed is modest — it requires 35 hours to travel 105 meters — it is still faster than other hydraulically powered robots in its category. The worm is particularly well-suited for exploring narrow spaces, such as pipes or tunnels, where it could one day be used for inspections or repairs.

The researchers have high hopes for the future of soft robotics. They envision a future in which robots with this type of battery will be given a skeletal structure that enables them to walk and perform other complex tasks. Such robots would move closer to mimicking natural organisms, with integrated systems that blur the lines between structure, power, and function.