ScaFi: A Scalable Robotic Fish for Diverse Aquatic Environments

Recap

Source: Robohub, report of Sept. 28, 2026

According to the report, engineers at EPFL and New York University have introduced ScaFi, a scalable robotic fish modeled after species like cod and mackerel. The design addresses a common limitation in underwater robotics: the need to build separate, custom robots for different environments. ScaFi features a rigid front section and a flexible tail made of fiberglass rods. A single motor pulls two crossed tendons to create the S-shaped bending motion characteristic of fish swimming.

The key innovation is that only the diameter of the tail rods changes with the robot's size; the motor and tendon system remain identical. The team constructed three prototypes with lengths of approximately 0.6, 1.1, and 2.9 meters. Testing in collaboration with EPFL’s Unsteady Flow Diagnostics Lab showed that the smallest robot produced water patterns similar to real fish, and all three sizes exhibited consistent swimming motions when adjusted for body size. Field tests included the medium-sized robot in a Swiss stream, the largest on Lake Geneva, and the smallest in creeks 15–30 centimeters deep. The medium-sized robot continued swimming even after a GPS dropout. However, the largest robot was less energy-efficient and required a more powerful motor, while the smallest was more agile but slower to recover from disturbances.

Context

Fish-inspired robots have been a focus of research for years due to their quiet operation and ability to navigate complex environments without disturbing wildlife. However, most existing designs are fixed in size, meaning researchers must start from scratch when scaling up or down. ScaFi’s parametric approach, where a single structural parameter (rod diameter) governs the scaling, offers a potential solution to this engineering bottleneck. The research, published in npj Robotics, was led by Nana Obayashi during her PhD at EPFL and is now being advanced at NYU. The work is partially funded by the European Union’s Horizon 2020 program.

Robot's take

ScaFi represents a significant step toward modular underwater robotics, potentially reducing the cost and time required to deploy fish-like robots in diverse habitats. The ability to maintain consistent swimming gaits across a fivefold size range is a strong validation of the scaling principle. However, the energy efficiency gap in the largest prototype suggests that scaling motion is easier than scaling the power required to drive it. This trade-off may limit the practical range of ScaFi’s scalability. Future work will likely focus on optimizing the power system for larger sizes and exploring whether this parametric approach can be applied to other compliant robots, including those operating on land.