Oceans cover most of the world and, unfortunately, are highly polluted. One strategy for combating the waste mounds found in these highly sensitive ecosystems – particularly around coral reefs – is to use robots to perfect the cleanup process. However, underwater robots are mostly bulky with rigid bodies, unable to explore and sample in complex, unstructured environments, and are noisy due to electric motors or hydraulic pumps. For a more appropriate design, scientists at the Max Planck Institute for Intelligent Systems (MPI-IS) in Stuttgart looked to nature for inspiration. They created a jellyfish-inspired, versatile, energy-efficient, and noise-free robot roughly the size of a hand. Jellyfish-Bot is a collaboration between the Physical Intelligence and Robotic Materials divisions of MPI-IS. A “Versatile Jellyfish-like Robotic Platform for Effective Underwater Propulsion and Manipulation” is published in Science advances.
To build the robot, the team used electro-hydraulic actuators through which electricity flows. The motors act as artificial muscles that power the robot. Surrounding these muscles are airbags as well as hard and soft components that stabilize the robot and make it waterproof. This way, the high voltage running through the actuators cannot contact the surrounding water. The power supply periodically delivers electricity through thin wires, causing muscles to contract and expand. This allows the robot to swim gracefully and create eddies under its body.
“When a jellyfish swims up, it can trap things along its path because it creates currents around its body. In this way, it can also collect nutrients. Our robot also circulates water around it. This function is useful for collecting things such as waste particles. It can then move garbage to the surface, where it can be recycled later. It is also able to collect fragile biological samples such as fish eggs. At the same time, there is no negative impact on the surrounding environment. The interaction with aquatic species is gentle and almost noise-free,” explains Tianlu Wang. He is a postdoctoral researcher in the Department of Physical Intelligence at MPI-IS and the publication’s first author.
His co-author Hyung Joon Joo from the Department of Robotic Materials continues: “70% of marine litter sinks to the sea floor. Plastic makes up more than 60% of this litter, and it takes hundreds of years for it to decompose. Therefore, we saw an urgent need to develop a robot to deal with things like Trash and move it up. We hope underwater robots will one day help clean up our oceans.”
Jellyfish-Bots can move and hold objects without physical contact, and operate either alone or with several objects in combination. Each robot runs faster than other similar inventions, reaching a speed of 6.1 cm/sec. Moreover, Jellyfish-Bot only requires a low input power of about 100mW. They are safe for humans and fish in case the robot’s insulating polymer material ever breaks. Meanwhile, the noise from the robot is indistinguishable from the background levels. This way Jellyfish-Bot gently interacts with its environment without disturbing it – just like its normal counterpart.
The robot consists of several layers: some serve to strengthen the robot, others serve to keep it afloat or isolate it. Another polymer layer acts as a floating skin. Electrically powered artificial muscles known as HASELs are fused in the middle of the different layers. HASELs are plastic bags filled with liquid insulators partially covered with electrodes. Applying a high voltage across an electrode causes it to be positively charged, while the surrounding water is negatively charged. This generates a force between a positively charged electrode and the negatively charged water that pushes the oil inside the bags back and forth, causing the bags to contract and relax – similar to a real muscle. HASELs can withstand the high electrical stresses generated by the charged electrodes and are protected against water by an insulating layer. This is important, because HASEL muscles have never been used before to build an underwater robot.
The first step was to develop a Jellyfish-Bot with a single electrode with six fingers, or arms. In the second step, the team divided the single pole into separate groups to move them independently.
“We achieved gripping by having four of the arms act as a propeller, and the other two as a gripper. Or we operated only a subset of the arms, in order to steer the robot in different directions. We also looked at how we could do this. It could power a group of several robots.” For example, we take two robots and let them pick up a mask, which is very difficult for one robot alone. Two robots can also cooperate to carry heavy loads. However, at this point, Jellyfish-Bot needs a wire. That’s a drawback if we really want to use it someday in the ocean,” says Hyeong-Joon Joo.
Perhaps the wires that power robots will soon be a thing of the past. “We aim to develop wireless robots. Fortunately, we have achieved the first step towards this goal. We have integrated all functional modules such as battery and radio communication parts to enable wireless manipulation in the future,” Tianlu Wang continues. The team attached a buoyancy unit to the top of the robot and a battery and microcontroller to the bottom. Then they took their invention for a swim in the pool of the Max Planck campus in Stuttgart, and were able to successfully steer it. However, they have not yet been able to direct the wireless robot to change course and swim the other way.