Water-Pumping Robot Climbs Slopes and Steps

Researchers at NYU Tandon School of Engineering have developed a soft-bodied robot that moves water between its head and tail to change its center of mass. This simple hydraulic mechanism allows the device, named WorMa, to climb steep inclines, step over obstacles, and swim using the same basic locomotion pattern. By shifting weight internally, the robot adapts its traction and propulsion without needing separate modes for different environments.

The approach offers a practical alternative to rigid legged robots, which often struggle with energy efficiency and complexity. By relying on fluid dynamics rather than heavy actuators, WorMa reduces the mechanical burden on its structure. This design philosophy suggests that soft robotics can handle diverse physical challenges with fewer moving parts, potentially lowering maintenance costs and increasing reliability in real-world applications.

Internal weight shifting boosts traction

On inclined surfaces, the robot’s ability to pump water toward its head is critical. This shift increases the downward force on the front contact points, providing the necessary friction to prevent sliding. In tests, this head-biased configuration was the only one that successfully carried the robot up the steepest slope tested at 19.5 degrees. Other weight distributions resulted in the robot sliding back down the incline.

Beyond just climbing, the weight shift significantly improves energy efficiency. The team measured a reduction in the cost of transport by at least 33 percent compared to other configurations. This efficiency gain is crucial for battery-powered robots, as it extends operational range and reduces the frequency of recharging. The trade-off is that the system relies on a sealed fluid loop, which adds internal complexity but eliminates the need for complex joint mechanisms.

Overcoming vertical obstacles with fluid

Navigating steps presents a different challenge that requires dynamic weight adjustment. A fixed heavy-head or heavy-tail configuration could not clear steps on its own. Instead, WorMa uses a sequenced approach: it first shifts water to the head for traction, then moves the fluid to the tail to raise the front end. Once the head anchors on the step's edge, the water shifts back to the head to continue the climb.

This coordinated sequence allows the robot to clear steps up to 15 centimeters high. The process demonstrates how internal fluid manipulation can substitute for complex leg articulation. While the movement is slower than a sprinting quadruped, it is highly reliable for steady, controlled ascent. The catch is that the robot must carefully time these fluid shifts, requiring precise sensors to detect contact points and step geometry.

Versatile design for varied terrain

The same undulatory gait that helps WorMa climb and step also enables it to swim. This amphibious capability makes it suitable for tasks like environmental monitoring or disaster response in areas with mixed land and water terrain. The robot’s soft body allows it to conform to surfaces, reducing wear and tear compared to rigid plastic or metal exoskeletons.

As reported by GN auto tech/robotics, this innovation highlights a shift toward simpler, fluid-based actuation in robotics. By avoiding the high cost and fragility of complex leg mechanisms, engineers can create robots that are easier to manufacture and repair. The primary limitation remains the speed of fluid transfer, which may restrict the robot’s agility in fast-paced environments. However, for steady, reliable traversal of rough terrain, this approach offers a compelling balance of efficiency and robustness.