Around the world, the oceans are struggling with ever-growing amounts of waste. More than 80% of marine
debris is plastic, and among that, microplastics; tiny plastic particles spread throughout the sea; are especially problematic. They are hard to decompose, are easily ingested by marine organisms,
and eventually accumulate in the human body as well.
When we contacted a marine cleaning company, we learned that no method yet exists that can collect
microplastics efficiently on a truly global scale. That gap motivated us to design and build an underwater
robot specifically aimed at collecting marine microplastics.
Instead of starting from scratch, we decided to imitate nature. Shellfish such as scallops naturally draw
large volumes of water through their bodies as they swim, and over their life cycle they accumulate
microplastics. Inspired by this, Team “Bbub bbub” from SIGMA (robotics club in Seoul National University) developed a low-power bio-inspired robot that
swims like a scallop while pulling in and expelling water, capturing microplastics in the process.
Fig 1. (Left) CAD design of the drive mechanism for the shellfish-inspired robot. The opening and closing of
the shell are driven by a motor and crankshaft that imitate the motion of a real scallop. (Right) Completed prototype of the shell robot. The body is 3D-printed and houses the motor,
electronics, and battery in a compact waterproof structure.
1. Purpose, Motivation, and Need
Microplastics are now widely distributed throughout the global ocean. Because they are so small and
persistent, they are easily eaten by fish, shellfish, and other organisms, and can cause harm not only to
those species but ultimately to humans.
After speaking with a marine cleaning company, we concluded that existing technologies do not yet offer a
practical, scalable way to collect microplastics across the world. We therefore decided to build a dedicated
underwater robot for this task.
For underwater robots, starting from a blank slate can be inefficient due to many constraints on structure,
power, and control. We believed a bio-inspired strategy would be more effective and chose the scallop as our
model. Its swimming mechanism and body structure are very simple, but existing research on applying them to
robotics is limited. At the same time, the scallop’s way of sweeping water volumes at various depths is
well-suited to gathering floating plastic.
Our final concept is a scallop-mimicking robot with an additional structure for capturing plastic. If that
collection structure is removed, what remains is a compact, low-power underwater robot platform with a wide
range of possible missions such as underwater exploration, educational use, and swarm-style multi-robot
systems.
Key characteristics of this platform are:
1) It moves with very low power consumption.
2) It is extremely light (about 200 g).
3) The structure is simple and can be miniaturized.
4) The bio-inspired motion is unlikely to strongly disturb marine ecosystems.
5) The small number of components keeps the cost low.
Through this project, we wanted to demonstrate that a robot with a simple, low-power actuation method can
still achieve practically meaningful mobility, and could serve as a basic platform for many surface and
underwater tasks, including microplastic collection.
2. Approach and Development Process
We began by studying how real scallops swim. A scallop opens its shell to draw in water, then rapidly closes
it to eject that water backward. The reaction force generated by this jet propels the animal forward. The
principle is simple yet powerful, and is attractive for underwater robotics because it simplifies fabrication,
favors compact designs, and adapts well to diverse environments.
Fig 2. Real scallop swimming by rapidly opening and closing its shell,
drawing in water and jetting it backward for thrust.
Before building the robot, we prepared the essential components: a DC motor, an Arduino board, a hinge shaft
for the shell, and batteries. Based on those, we designed the shell body and crank mechanism in 3D CAD, then
printed them using ABS filament. In this way we could maintain a low overall weight even with a relatively
large body.
To reduce the size of the electronics, we used an Arduino Nano, whose small footprint and easy programming
also helped minimize control errors when operating underwater.
Because the robot must work in water, waterproofing was a central issue. We tried various methods on the
electronics, including waterproof spray, HDPE sealing wrap, hot-melt adhesive (HMA), cyanoacrylate adhesive,
paraffin wax, and direct heating of plastic. Through repeated underwater experiments we found that a
combination of spray coating, sealing wrap, and candle wax provided the most reliable protection.
To improve propulsion, we attached a membrane to the front part of the shell. When the shell opens, incoming
water is redirected so that it exits only toward the rear, increasing net thrust. We tested several candidate
materials: nylon stockings, rash-guard fabrics (spandex, nylon, polyester blends), polyester umbrella
fabric, and raincoat material. Umbrella fabric performed best and was chosen for the final prototype.
3. Robot Design and Performance
In designing the robot, we focused on three elements: the shape of the shell, the geometry of the crankshaft,
and the balance between thrust and lift.
The shell was modeled to resemble a real scallop while also having an airfoil-like cross-section. As the
shell opens and closes rapidly to propel the robot, this shape helps generate a small upward lift, so the
robot slightly rises as it moves forward.
The robot ejects water through a small orifice at the rear of the body. Unlike a real scallop, however, we
attached a membrane at the front that essentially blocks flow through the front opening. Because of this,
there is a risk of reverse thrust as water flows in from the rear when the shell opens.
To address this, we derived the thrust expression for fluid exiting a jet orifice and found that the closing
phase must be faster than the opening phase to ensure net forward thrust. We implemented this condition in
the control code so that the robot consistently moves forward rather than backward.
In the future, replacing the fully blocking membrane with a flexible flap valve could allow water to be
drawn in from the front and expelled to the rear, generating thrust both during intake and exhaust and
further improving swimming efficiency.
The crankshaft length was calculated so that the shell could open up to about 30 degrees. Most of the
critical mechanical parts; the two shell halves and the crankshaft; were fabricated on a
3D printer, simplifying manufacturing and keeping the cost down.
The final robot consists of two shells, a motor and crankshaft, the front membrane, an Arduino Nano, an
ultrasonic distance sensor, and a battery pack. For the battery we used several 1.5 V cells connected in
series to provide about 12 V, which is inexpensive yet sufficient for actuation. The ultrasonic sensor
is used to detect obstacles in front of the robot.
To evaluate mobility, we recorded the robot’s motion on video. Each open–close cycle moved the robot roughly
5 cm forward, and its maximum speed was about 10 cm/s. Considering the simplicity of the
components, these values show that even a very simple system can achieve meaningful underwater mobility.
Fig 3. (Left) Distribution of simulated plastic particles in the water before the robot operates. (Right) The shell robot in the process of collecting floating plastic fragments during a tank
experiment.
As an example mission for the shell robot, we tested whether it could collect plastic fragments scattered in
a tank. The robot captured roughly 50–60% of the fragments in the target area, showing that its basic
design can already perform the intended task at a practically meaningful level.
4. Expected Effects and Applications
The shell robot is about 15 cm wide and long and 5 cm high: roughly the size of a small fish
or large shellfish. This compact form gives it high accessibility, even in tight or cluttered environments.
The total cost of the final prototype was under 100 USD, thanks to the simple circuit and inexpensive
components. Combined with the low power requirement of around 12 V, this makes the robot suitable for
mass production and long-term operation in the ocean without large external power systems.
The shell shape also improves durability. Like a real scallop shell, the grooves in the 3D-printed body help
distribute external forces toward the hinge and outer edges. As a result, collisions with docks or rocks are
less likely to damage the internal components or crack the shell.
Existing microplastic treatment technologies, such as membrane bioreactors (MBR) or electrocoagulation,
suffer from low efficiency or risk of environmental side effects. In contrast, the shell robot can be
produced in large numbers, is unlikely to significantly harm other marine organisms, and allows the rate of
microplastic collection to be scaled simply by deploying more units.
If we attach a LiDAR or similar sensor, the robot could estimate the local concentration of microplastics and
adapt its behavior accordingly, further improving efficiency. Replacing the motor-based mechanism with soft
actuators or pneumatic artificial muscles is another promising direction that could simplify manufacturing and
further reduce environmental impact.
A particularly interesting future direction is to deploy many shell robots as a swarm system. With networking
and simple coordination, a group of robots could perform underwater tasks such as exploration or
environmental monitoring far more efficiently than a single unit.
Beyond environmental cleanup, the shell robot platform has many potential uses. Its simple motion and
biological inspiration make it suitable for educational purposes, and its low cost and robustness make it
attractive for research on swarm robotics or underwater sensing.
In short, when used for microplastic collection the shell robot can provide efficient treatment, and even as a
standalone platform it offers strong advantages in versatility, cost-effectiveness, and durability.
5. Cost Analysis and Team Roles
Cost (approx.)
– Electronics (Arduino Nano, motor driver, batteries): 27,000 KRW
– 3D printing (outsourced): 69,000 KRW
– Mechanical parts (screws, nuts, wires, adhesives): 3,000 KRW
Total: 99,000 KRW (≈ 99 USD)
Team (All participants contributed equally): Seongjun Park, Jiwon Kim, Junseok Yoo, Sookwan Han
6. References
1. Jeon, Y.-H. (2018). Distribution and significance of microplastics in the ocean: sources, mechanisms,
effects, and potential solutions. Korea Institute of Science and Technology Information.
https://doi.org/10.22800/KISTI.KOSENEXPERT.2018.5
2. Chae, S.-W. (2018, December 17). “A single shellfish may contain billions of plastic particles.”
Green Post Korea. URL: http://www.greenpostkorea.co.kr/news/articleView.html?idxno=99391
3. White, F. M. (2017). Fluid Mechanics. McGraw-Hill.
