The Soft Fish Robot, or SoFi, is a biomimetic autonomous underwater vehicle developed by the Massachusetts Institute of Technology’s CSAIL. Designed to closely mimic the appearance and movement of a real fish, SoFi can swim freely in the ocean without the need for a tether. This innovative technology allows researchers to observe fish in their natural habitat without causing disturbance. The robot represents a significant advancement in non-invasive ocean research, offering a new perspective on the underwater world that was previously difficult to obtain.
The Innovative Design of SoFi
The construction of SoFi relies on the principles of soft robotics, which prioritizes flexible materials over rigid structures. The entire back half of the 18.5-inch robot is composed of silicone rubber and flexible plastic, allowing for the smooth, undulating body movements seen in real fish. This soft exterior is more forgiving in confined environments, making the robot less likely to damage fragile ecosystems like coral reefs upon collision.
The robot’s head, which houses the electronics, is 3D-printed for structural integrity. Within this enclosure are a lithium polymer battery, a single motor, and a high-resolution camera equipped with a fisheye lens. To protect these internal components from the immense pressure changes during dives, the electronics are sealed in a water-tight compartment often filled with a small amount of baby oil, a fluid that resists compression. This combination of soft body and protected internal hardware allows SoFi to operate effectively at depths exceeding 50 feet.
How SoFi Navigates Underwater
SoFi’s movement is driven by a hydraulic propulsion system that expertly mimics the motion of a fish’s caudal fin. The system uses a single motor to pump water into two chambers located in the tail section. As the motor alternates the flow, one chamber expands while the other contracts, causing the flexible tail to bend side-to-side in a wave-like action.
This alternating movement generates the thrust needed to propel the robot forward at an average speed of about half a body length per second. The robot achieves vertical movement using an internal buoyancy control unit (BCU) that adjusts its density by compressing and decompressing air. SoFi also has two small fins, known as dive planes, on its sides that allow it to tilt its body for controlled diving or surfacing. Researchers control SoFi remotely using a custom acoustic communication system, which transmits ultrasonic pulses between 30 and 36 kilohertz to a receiver on the robot.
Real-World Applications and Research
The primary application of SoFi is the non-invasive observation of marine life and ecosystems, offering scientists a powerful new field tool. During initial testing in the Rainbow Reef in Fiji, the robot successfully swam alongside schools of fish for up to 40 minutes without causing them to scatter. Its ability to maneuver through strong currents while remaining untethered allows for prolonged study in challenging, dynamic environments.
The onboard fisheye camera captures high-resolution photographs and video, providing detailed documentation of fish behavior difficult to obtain through human diving or traditional robotics. Scientists use this observational data to monitor the health of sensitive environments, such as documenting the condition of coral reefs or tracking the movement patterns of specific marine species. Researchers are also exploring its potential for gathering sensor data, like measuring pollution levels or temperature gradients in coastal waters.
Advantages Over Traditional Underwater Vehicles
SoFi offers distinct advantages over conventional Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs), primarily due to its biomimetic design. Traditional vehicles rely on noisy propellers or water jets for propulsion, creating turbulence and sound that often startle marine animals and disrupt their natural behavior. In contrast, SoFi’s silent, undulating tail movement allows it to blend in seamlessly with its environment, enabling genuine, close-range observation.
The soft body construction also makes SoFi inherently safer for the underwater world it studies. The risk of damaging fragile coral or injuring marine life during accidental contact is minimized compared to rigid, metal-bodied robots. This combination of quiet operation, non-disruptive presence, and superior maneuverability in tight spaces makes the soft robotic fish a more effective choice for gathering true-to-life data on the ocean’s inhabitants.