Development of shape memory alloy actuated caudal fin soft robotic fish propulsion system

We present shape memory alloy (SMA) driven caudal fin soft robotic fish propulsion system. The goal of the project is to build a bio-inspired, soft robotic underwater vehicle that swims and maneuvers quietly and efficiently, much like a real biological fish, without using traditional mechanical motors that produce noise. The vehicle is modeled (shape, size, and mechanics of motion) after the Wahoo fish (Acanthocybium solandri) which can swim efficiently at a high speed. The vehicle’s propulsion thrust is produced by the undulating motion of the back half of the body that produces wave-like motions when actuated. The propulsion is achieved by actuating coiled SMA elements that span successive cross section ribs, on the port and starboard sides, of the vehicle that are designed to pivot at the midpoint of the vehicle. All successive ribs are connected at the midpoint by linkages mimicking the vertebra in a fish, which allow each rib to pivot at the end of the link to which it is attached. Alternating the actuation (turning the current on and off) of the SMA elements on the port and starboard sides produces the desired undulating motion, currently at a frequency of 0.5Hz. The alternate actuation scheme allows the SMA elements to cool down before the next actuation sequence. The thrust produced were measured by mounting the propulsor on a 3-axis load cell in a water tank and recording the force generated at various power levels applied to the SMA actuators. The thrust increases as the power supplied to the actuators were increased. Computational Fluid Dynamics (CFD) simulation is then used to estimate the achievable speed for the full vehicle model at a given thrust level. Inversely, the CFD model is then used to predict the required thrust/force level to achieve the desired vehicle speed. Building upon some preliminary results, we are working on optimizing the kinematic designs, actuator configurations and strategies to achieve higher undulating frequency and thrust to develop a soft robotic fish that can achieve high speed.