Jellyfish are energy-efficient swimmers due to the muscle-powered flapping of their soft bell that facilitates a unique energy recapture mechanism. In this paper, we present a bio-inspired jellyfish robot named Poly-Saora that mimics the swimming behavior of the jellyfish species Black sea nettle (Chrysaora achlyos). An assembly-based fabrication method is used to create the Poly-Saora that is developed mainly with polymeric materials (95% of the robot by volume). Twisted and coiled polymer (TCP) actuators are successfully implemented in this robot and show great potential for underwater applications. The influence of different parameters such as the amplitude of the input power, the actuation frequency, and the lifecycle of the actuator are investigated underwater. A full characterization of 6-ply TCP muscles is demonstrated. An actuation strain of ∼10% is achieved in water at a frequency of 0.1 Hz and 50 kPa load. When integrated into the jellyfish, the TCP was able to bend a single bell by 17°. Poly-Saora was able to swim a vertical distance of 180 mm in 220 s with four TCP actuators each confined in a separate conduit. The robot mimics the swimming behavior of a real jellyfish by contracting the bell segments through the activation of the actuators, which generates forced water circulation under the bell in a pulsating rhythm, consequently creating a vertical movement of the robot. Overall, Poly-Saora presents a model of an underwater system that is driven by stimuliresponsive polymer materials and has unique advantages over conventional rigid robots due to their lightweight, muscle-like structures, silent actuation and ease of manufacturing. This robot can be used for safe interaction with other underwater species and their natural habitats when fully developed.

Exploring the world beneath the ocean has been a difficult task, especially in depths that are unsafe for humans. Studying underwater creatures can be very sensitive due to disturbances resulting from typical remotely operated vehicles (ROVs) currently used. Soft robots consist of elastomeric materials, compliant actuators, sensors and other supporting structures, which enable them to be used for numerous applications due to their flexibility, light weight, low noise, and many degrees of freedom. Mechanical actuators, such as pneumatic actuators and servomotors, introduce design constraints related to their size, weight, and cost. Moreover, vibration and noise are undesired attributes that preclude the use of robots developed with such technologies and might disturb the test environment. This paper presents a robust design of a jellyfish-like robot with eight bell segments, named KryptoJelly. The presented robot can perform multidirectional swimming by NiTi shape memory alloys (SMA) actuators confined in a conduit and activated by electrical current stimulation. KryptoJelly is constructed from a 3D printed rigid structure and a soft silicone bell that closely mimics the biological locomotion and appearance of a jellyfish found in nature; the Chrysaora colorata species. Four 127 µm diameter SMA wires (of mass 14 mg each) were used per channel to deform the silicone bell margin. The robot can operate up to 1608 cycles continuously for 1.5 h underwater at high power input (3 times higher than the standard) and sustain its own total body mass of 650 g (~6000 times the weight of the actuators used). KryptoJelly is able to maneuver in both vertical and horizontal directions during bell contraction-expansion cycles. A study on the effect of multistage-power-time input sequence of NiTi SMA actuators and bell design, which results in swimming, is presented. This work has shown the great potential of employing smart materials in biomimetic soft robots, that can be deployed for eco-friendly underwater exploration or other applications.

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Researchers are seeking to create robots that could conform to non-uniform objects during handling and manipulation. High performance artificial muscles are the key factors that determine the capabilities of a robot. Twisted and coiled polymeric (TCP) muscle embedded in soft silicone skin solves some of the problems of soft robots in attaining morphed structure using low voltages, contrary to other technologies such as dielectric elastomer and piezoelectric. Furthermore, the TCP actuation system does not generate noise like pneumatic systems. The TCP embedded skin shows great promise for robotics to mimic the flexible appendages of certain animals. In this paper, we present experimental results on the effect of muscle placement and the thickness of the artificial skin on the actuation behavior, which can be used as a benchmark for modeling. We demonstrate the effect of three different skin thicknesses and three different muscle locations within the skin, by taking experimental deformation data from stereo camera. In general, two modes of actuations (undulatory and bending) were observed depending on the muscle placement, skin thickness, applied voltage, and actuation time. The thinner skin showed two-wave undulatory actuation in most cases, whereas the 4 mm skins showed mixed actuation and the 5 mm skins exhibited one-wave undulatory actuation. In all cases, the increase in voltage resulted in higher magnitudes of actuation. In addition, we showed consistent strain of the TCP muscles from 18 samples from two batches that produced an average strain of 22% (batch 1) to 20% (batch 2) with standard deviation of 2.5-1.8% respectively.

Underwater exploration or inspection requires suitable robotic systems capable of maneuvering, manipulating objects, and operating untethered in complex environmental conditions. Traditional robots have been used to perform many tasks underwater. However, they have limited degrees of freedom, manipulation capabilities, portability, and have disruptive interactions with aquatic life. Research in soft robotics seeks to incorporate ideas of the natural flexibility and agility of aquatic species into man-made technologies to improve the current capabilities of robots using biomimetics. In this paper, we present a novel design, fabrication, and testing results of an underwater robot known as Kraken that has tentacles to mimic the arm movement of an octopus. To control the arm motion, Kraken utilizes a hybrid actuation technology consisting of stepper motors and twisted and a coiled fishing line polymer muscle (TCPFL). TCPs are becoming one of the promising actuation technologies due to their high actuation stroke, high force, light weight, and low cost. We have studied different arm stiffness configurations of the tentacles tailored to operate in different modalities (curling, twisting, and bending), to control the shape of the tentacles and grasp irregular objects delicately. Kraken uses an onboard battery, a wireless programmable joystick, a buoyancy system for depth control, all housed in a three-layer 3D printed dome-like structure. Here, we present Kraken fully functioning underwater in an Olympic-size swimming pool using its servo actuated tentacles and other test results on the TCPFL actuated tentacles in a laboratory setting. This is the first time that an embedded TCPFL actuator within elastomer has been proposed for the tentacles of an octopus-like robot along with the performance of the structures. Further, as a case study, we showed the functionality of the robot in grasping objects underwater for field robotics applications.