Made entirely out of plastic on a multi-material 3D printer, ETH Zürich’s mini submarine presents a crucial stroke forward for the future of smart devices.
The 7.5 centimeter long vehicle is capable of paddling forwards, delivering cargo, and returning to base, all without an engine, propellant, or power supply.
An impressive feat combining materials science, computing and engineering, the mini-sub concept has been created under the direction of ETH Professor Kristina Shea in collaboration with researchers at Caltech in Pasadena.
Transformation by 4D printing
The motorless submarine is made using a 4D printed material concept previously presented by Shea and doctoral student Tim Chen in open article for Nature’s Scientific Reports journal.
In this article the authors detail how 3D printed objects can be pre-programmed to transform into a different shape – taking advantage of plastic’s response to heat.
The mini-submarine design is a more sophisticated application of heat-activated actuators detailed in this previous study, relying on the staggered activation of three separate actuator sets.
Row row row your sub
Placed on each set of paddles and a gripper attached to the top, the submarine’s 4D printed actuators are programmed to expand in response to water temperature.
In the first stroke: expansion takes place, the actuator moves, and the transformation generates a simultaneous stroke forward of the attached paddles.
For the stroke back to base: actuators on the second set of paddles thicker than those in the first set, meaning that the plastic of the actuators takes longer to heat up, expand, and generate a stroke.
Deposit of cargo, in between the two strokes, is dictated by the same material reaction, with actuators made at a thickness between those on the paddles.
Exploring the possibilities
The submarine’s swimming process is similar to the way our muscles expand and contract to create movements. However, at present, the submarine would have to be reset to perform more than one stroke/action per set of actuators.
Eventually, the team will be able to create sophisticated series of multiple 4D printed actuators to enable further activity of vehicles in water. The researchers also hope to expand the research to include materials that react to other environmental factors, such as water salinity or acidity.
The supporting paper for this work, “Harnessing bistability for directional propulsion of soft, untethered robots” is published in PNAS journal. It is co-authored by Tian Chen, Osama R. Bilal, Kristina Shea and Chiara Daraio.
Featured image shows the visualization of a simple mini-submarine with two paddles. Image via ETH Zurich / Tim Chen