Potential for clean-up and sampling: German researchers have developed biologically-inspired underwater robots that can use the power of artificial muscles to swim and sense objects. Flow effects enable them to do this without touching them, but the jellyfish bots can also grab “hand-tight”. They could one day be used to collect debris from sensitive environments like coral reefs or gently collect biological samples, the developers say.
Bulky and driven by whirring propellers – aquatic robots are mostly rigid and noisy, which makes their use in complex and sensitive underwater worlds problematic: The “technical monsters” can disturb living beings there or damage delicate structures. In order to develop gentler robotic systems, scientists are now also taking inspiration from the creatures in the underwater world. Concepts of so-called soft robotics have already resulted in versions that glide pulsating through the water – i.e. are modeled on jellyfish. However, the performance of these systems has so far left a lot to be desired.
Vegetable oil sachets as muscles
However, the concept presented by the researchers from the Max Planck Institute for Intelligent Systems (MPI-IS) in Stuttgart could now lead to the development of really practical jellyfish robots. Their hand-sized jellyfish bots also glide silently through the water with pulsating movements. The innovative thing is that this is based on the contractions of arms equipped with artificial muscles. These are plastic bags filled with vegetable oil that are activated by electrical charging. In addition to effective and energy-efficient locomotion, the strong arms also enable the jellyfish bots to grip.
The entire construction is made up of several soft and firm components: some stabilize the umbrella-shaped structure, others make it buoyant. A polymer structure on the arms acts as a web. For the movements, the artificial muscles are positively charged by applying a voltage. In combination with the negatively charged surrounding water, this creates a force that moves the oil within the bag, the scientists explain. In this way, the bags can be contracted and relaxed – similar to real muscles.
The system prototype has six arms equipped in this way, which can be controlled together or independently. This allows the robot to be steered while swimming. At up to 6.1 centimeters per second, it achieves higher speeds than previous systems, but only requires a low power of around 100 milliwatts, the developers report.
Waste under control
The robot can detect objects in two different ways – jellyfish-like without contact or “hand-on”. “When a jellyfish swims up, it can catch objects in its path because it creates currents around its body. This is also how she collects her nutrients. Our robot also circulates the water around it,” explains lead author Tianlu Wang from the MPI-IS. This creates a flow system that allows the Jellyfish bot to collect small and light objects without contact, tests have shown. “For example, it can transport waste particles to the surface, where they can later be recycled. In this way, he would also be able to collect biological samples such as fish eggs,” says Wang.
His colleague Hyeong-Joon Joo explains the other gripping function: “The robots can also grasp objects by using four of the arms to swim and the other two as grippers”. Several robots can also work together: “For example, we had two robots lift a corona protective mask, which is very difficult for a single robot. They can also work together to carry heavy loads,” says Joo.
The developers are convinced that the test results of the prototype show potential: “We hope that one day underwater robots will be able to help clean up our oceans,” says Joo.
In order to realize this vision, the team is now working on further optimizing the concept. In the future, the robots should consist entirely of biodegradable components, and the researchers are primarily working on the power supply and control. “Fortunately, we have taken the first step towards a wireless system: we have installed all the functional modules such as the battery and the control units,” says Wang. The researchers have already successfully tested this version of the Jellyfish bot in a pond on the Max Planck campus in Stuttgart. As they report, however, there is still a need for optimization in terms of steerability.
Video: © MPI-IS
Source: Max Planck Institute for Intelligent Systems, specialist article: Science Advances, doi: 10.1126/sciadv.adg0292