In a proof-of-concept study, researchers from ETH Zurich and Caltech in Pasadena, CA have demonstrated a new propulsion system for motorless swimming robots. Unlike traditional aquatic mechanisms which rely on propellants or engines to move in water, the swimming robots—made entirely from 3D printed parts—use fluctuations in water temperature to propel themselves.
A recent study published in the journal PNAS details how the researchers, led by ETH Professor Kristina Shea, created a small (7.5 cm) mini-submarine with 3D printed paddles that could showcase this propulsion technique.
Manufactured using a multi-material 3D printer, the paddles integrate shape memory polymer strips which expand when placed in heated water. These polymer strips, developed by Shea and doctoral student Tim Chen, effectively power the boat using a bistable propulsion element which moves the paddles as water temperatures change.
More specifically, the polymer strips in the paddles expand when heated which causes the bistable element to “quickly snap” resulting in a stroke motion. The researchers have also found a way to maintain control of the paddles’ directional motion, force and timing by adapting the robot’s geometry and material.
“A major challenge in soft robotics is the integration of sensing, actuation, control, and propulsion,” the researchers write in their study. “Here, we propose a material-based approach for designing soft robots. We show an untethered, soft swimming robot, which can complete preprogrammed tasks without the need for electronics, controllers, or power sources on board.”
Admittedly, the research is still in its early stages, as each actuating element in the motorless aquatic robot can only complete a single paddle stroke before being manually reprogrammed. Still, by integrating multiple actuators, the researchers have demonstrated that a single motorless vessel can perform a range of functions.
As the ETH Zurich team demonstrates in a video, a 3D printed mini-submarine equipped with multiple actuators is capable of paddling forward once, dropping its cargo (a small coin, in this case) and paddling backwards to its starting position. The varied timing of the actuators was accomplished by tweaking the geometry of the 3D printed polymer “muscles.” For example, because thinner polymer strips heat up faster in warm water, they have a faster response than thicker ones.
“The main takeaway from our work is that we have developed a new and promising means of propulsion that is fully 3D printed, tuneable and works without an external power source,” commented Professor Shea.
Down the line, the motorless propulsion system could be explored for developing low-power vessels for underwater exploration. The researchers have also suggested they will investigate the ability to use environmental factors, such as the acidity or salinity of water, as triggering elements instead of temperature.