Soft Fish

Exploration of Underwater Life with an Acoustically-Controlled Soft Robotic Fish

Soft robotic fish SoFi swimming with real fish in a coral reef

Closeup exploration of underwater life requires new forms of interaction, using biomimetic creatures that are capable of agile swimming maneuvers, equipped with cameras, and supported by remote human operation. Current robotic prototypes do not provide adequate platforms for studying marine life in their natural habitats. This work presents the design, fabrication, control, and oceanic testing of a soft robotic fish that can swim in three dimensions to continuously record the aquatic life it is following or engaging. Using a miniaturized acoustic communication module, a diver can direct the fish by sending commands such as speed, turning angle, and dynamic vertical diving. This work builds on previous generations of robotic fish that were restricted to one plane in shallow water, and lacked remote control. Experimental results gathered from tests along coral reefs in the Pacific Ocean show that the robotic fish can successfully navigate around aquatic life at depths ranging from 0 to 18 meters. Furthermore, our robotic fish exhibits a lifelike undulating tail motion enabled by a soft robotic actuator design that can potentially facilitate a more natural integration into the ocean environment. We believe that our study advances beyond what is currently achievable using traditional thruster-based and tethered autonomous underwater vehicles, demonstrating methods that can be used in the future for studying the interactions of aquatic life and ocean dynamics.

Link to Full Text (Science Robotics)

R. Katzschmann, J. Delpreto, R. MacCurdy, D. Rus, “Exploration of Underwater Life with an Acoustically-Controlled Soft Robotic Fish.” Science Robotics, Mar 2018. [PDF]

News Articles on SoFi (Mar. 2018): “Soft robotic fish swims alongside real ones in coral reefs” featured in:
The New York Times, The Wall Street Journal, National Geographic, Reuters, BBC, NBC News, Nature, CNN, Wired, CNBC, TechCrunch, LA Times, NPR, CNET, Mashable, The Verge, Forbes, IEEE Spectrum, Popular Mechanics, Science Magazine, Scientific American, etc.

Hydraulic Soft Robotic Fish

Fish Underwater

A soft fish tail replaces a complex multi-link rigid fish body for biomimetic locomotion. This work presents aa soft-bodied robotic fish that is hydraulically actuated and capable of sustained swimming in three dimensions. A new closed-circuit drive system that uses water as a transmission fluid is used to actuate the soft body. Circulation of water through internal body channels provides control over the fish’s caudal fin propulsion and yaw motion.  A new fabrication technique for the soft body is described, which allows for arbitrary internal fluidic channels, enabling a wide-range of continuous body deformations.  Furthermore, dynamic diving capabilities are introduced through pectoral fins as dive planes. These innovations enable prolonged fish-like locomotion in three dimensions.

R. Katzschmann, A. Marchese, D. Rus. “Hydraulic Autonomous Soft Robotic Fish for 3D Swimming.“ ISER, Marrakech, Morocco, June 2014. [PDF]

Cyclic Actuation

Cyclic actuation

Various pump mechanisms are presented for soft undulating actuation in water. Undulating structures are one of the most diverse and successful forms of locomotion in nature, both on ground and in water. This work presents a comparative study for actuation by undulation in water.
We focus on actuating a 1DOF systems with several mechanisms. A hydraulic pump attached to a soft body allows for water movement between two inner cavities, ultimately leading to a flexing actuation in a side-to-side manner. The effectiveness of six different, self-contained designs based on centrifugal pump, flexible impeller pump, external gear pump and rotating valves are compared. These hydraulic actuation systems combined with soft test bodies were then measured at a lower and higher oscillation frequency. The deflection characteristics of the soft body, the acoustic noise of the pump and the overall efficiency of the system are recorded. A brushless, centrifugal pump combined with a novel rotating valve performed at both test frequencies as the most efficient pump, producing sufficiently large cyclic body deflections along with the least acoustic noise among all pumps tested. An external gear pump design produced the largest body deflection, but consumes an order of magnitude more power and produced high noise levels. Further refinement remains on determining the suitable oscillation frequencies and inner cavity designs for optimal efficiency and movement.

R. Katzschmann, A. de Maille, D. Dorhout, D. Rus, “Cyclic Hydraulic Actuation of Soft Robotic Devices,” IROS, Daejeon, Oct. 2016. [PDF]

Remote Control

Remote Control

An end-to-end compact acoustic communication system designed for easy integration into remotely controlled underwater operations. The system supports up to 2048 commands that are encoded as 16 bit words. We present the design, hardware, and supporting algorithms for this system. A pulse-based FSK modulation scheme is presented, along with a method of demodulation requiring minimal processing power that leverages the Goertzel algorithm and dynamic peak detection. We packaged the system together with an intuitive user interface for remotely controlling an autonomous underwater vehicle. We evaluated this system in the pool and in the open ocean. We present the communication data collected during experiments using the system to control an underwater robot.

J. Delpreto, R. Katzschmann, R. Maccurdy, and D. Rus, “A Compact Acoustic Communication Module for Remote Control Underwater.” Invited: ACM WUWNET, Washington D.C., USA, Oct. 2015. [PDF]

Link to Soft Robotic Fish Project at DRL, CSAIL, MIT