These young inventors had to make like a crab

Broadcom MASTERS finalists design and build a robotic arm by mimicking a crustacean
Nov 30, 2016 — 12:00 pm EST
crab engineering

Karen McDonald of the Smithsonian Environmental Research Center shows a crab shell to students participating in the Broadcom MASTERS competition.

E. Brady Robinson/SSP

WASHINGTON, D.C. —  When engineers tackle a design, they often copy one that has already evolved in some creature or plant. That’s called biomimicry. Finalists at this year’s Broadcom MASTERS research competition got a taste of how engineers do this. They had to design and build a working model of a robotic arm. These young designers had to base theirs on a crab claw — and finish it in less than two hours.

Broadcom MASTERS brings together 30 middle-school students each year for a special competition. (MASTERS stands for Math, Applied Science, Technology and Engineering for Rising Stars.) The program was created by Society for Science & the Public, which publishes Science News for Students. Broadcom Foundation sponsored the event. Unlike most science competitions, some 75 percent of a finalist’s score will come from how well they innovate and work with teammates on challenges. Only about one-fourth of their overall score will be based on the science-fair project they presented to judges earlier in the week.

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Students on the Black Team discuss the design of their crab-inspired arm. Shown counterclockwise from lower left: Ananya Ganesh, 14; Maya Chandar, 13; Akhilesh Balasingam, 13; and Brendan Crotty, 14.
E. Brady Robinson/SSP

This year, the students faced stiff challenges. They built complicated electronic circuits. They designed games that taught users about nutrition. But their final and most grueling challenge was the robotic arm.

“I liked this challenge the best,” says Nikolai Ortiz. This 13-year-old hails from Corpus Christi, Texas. Of all the week’s challenges, he notes, this engineering task was most like a project someone would encounter in the real world. Also, he brags, “our team had some really creative ideas.”


Their inspiration

The challenge took place at the Smithsonian Environmental Research Center, or SERC, in Edgewater, Md. This center sits along the shore of the Rhode River, a short waterway that flows into the Chesapeake Bay.  This huge  bay hosts plenty of Atlantic blue crab. And that’s the species that inspired this challenge.

The first step in biomimicry is learning about the species being mimicked. The students learned that their crab’s scientific name is Callinectes sapidus. Roughly translated from Latin, it means “beautiful tasty swimmer,” says Karen McDonald. She’s an environmental scientist at SERC. And although this crab is often called the Chesapeake blue crab, it also swims in the waters of the western Atlantic and Gulf of Mexico. Tens of millions are caught and eaten each year.

These crabs can grow up to 23 centimeters (9 inches) across. But they start out hatching from eggs about the size of a grain of sand. Like many shelled creatures, they molt, or shed their shell, as they grow.

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The White Team builds its hydraulic arm with hot glue. From left: Kaien Yang, 14; Santiago Stone, 15; Ashini Modi, 12; Omar Majzoub, 14; and Cynthia Chen, 14.
Linda Doane/SSP

In all, this species will molt 27 times, notes McDonald. Each time it molts, the crab becomes vulnerable to predators. That’s because to squeeze out of the old shell, its new shell must be very soft and flexible. The new shell doesn’t completely harden until 2 to 3 days after it has been exposed to water.

During that short interval, the crab can’t move like it normally does. When the crab’s shell is hard, muscles can pull against it. (This is similar to how people move, except our hard parts are the bones inside, not shells on the outside.) But when the crab’s shell is soft, muscles have nothing firm to pull against. So instead, the crabs use their muscles to pump fluid around inside their bodies. This pressurized fluid, like air moving in and out of a balloon, causes movement, explains McDonald. And this is where the Broadcom MASTERS challenge took its inspiration.

The engineered design

The students worked in teams of five. Each was named for a color. Their crab-inspired robotic arms would have to be powered by that movement of fluid, not by a muscle-like pull on a string. (The science of using the movement of liquids to exert force or control is known as hydraulics.) The engineered arm would be something that might be attached to an underwater vehicle and used to explore the ocean. It had to rotate through an angle of at least 90 degrees at its “elbow.”

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The Purple Team tests its arm. Shown from left: Aria Eppinger, 15; Anushka Naiknaware, 13; Lucas Ritzdorf, 14; Rachel Pizzolato, 12; and Nathan Deng, 14.
Linda Doane/SSP

To provide hydraulic force for these robotic arms, the teams could use syringes, rubber tubing and water. They also had a variety of wooden components to choose from when building their devices. These included small slabs, wooden disks and craft sticks. The teams could use glue, paper clips, tape or rubber bands to hold their devices together.

After taking a half-hour to design their projects (and a quick lunch that didn’t include crab cakes), the students had 90 minutes to build their robot arm.

All six teams worked separately. Each took a slightly different approach. Some used hydraulics to both extend and retract their arm. Others used hydraulics to extend their arm but rubber bands to retract it. During the building process, there was much trial and error — and many false starts. Some designs had to be modified or even totally scrapped. In the end, some arms worked much better than others.

At the close of the challenge, each team discussed its design and demonstrated its action. “I’m amazed at how well you did with this design challenge,” McDonald told the finalists. “You worked really well as teams.”

As the finalists took their robotic arms apart and stored the pieces they’d used, McDonald told me she was very impressed with their end results. Indeed, she said, “I’m not sure our [SERC] engineers could have come up with something in just two hours.”

Power Words

(for more about Power Words, click here)

angle     The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.

Atlantic     One of the world’s five oceans, it is second in size only to the Pacific. It separates Europe and Africa to the east from North and South America to the west.

biomimicry     The creation of new devices or techniques based on those seen in living organisms.

Broadcom MASTERS     Created and run by the Society for Science & the Public, Broadcom MASTERS (Math, Applied Science, Technology and Engineering Rising Stars) is the premier middle school science and engineering fair competition. Broadcom MASTERS International gives select middle school students from around the world a unique opportunity to attend the Intel International Science & Engineering Fair.

circuit     A network of that transmits electrical signals. In the body, nerve cells create circuits that relay electrical signals to the brain. In electronics, wires typically route those signals to activate some mechanical, computational or other function.

component     An item that is part of something else, such as pieces that go on an electronic circuit board.

degree     (in geometry) A unit of measurement for angles. Each degree equals one three-hundred-and-sixtieth of the circumference of a circle.

engineer     A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

engineering     The field of research that uses math and science to solve practical problems.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create for that organism or process. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature, humidity and placement of components in some electronics system or product.

force     Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.

glue     A sticky substance that attaches one material to another.

hydraulic      (n. hydraulics)  An adjective that refers to the movement of liquids under pressure in pipes and other confined spaces. The science of using the movement of liquids to exert force or control is known as hydraulics. The equipment used to provide such control are commonly referred to as hydraulics as well.

model     A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes.

muscle     A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in a protein, which is why predatory species seek prey containing lots of this tissue.

nutrition     (adj. nutritious) The healthful components (nutrients) in the diet — such as proteins, fats, vitamins and minerals — that the body uses to grow and to fuel its processes.

predator     (adjective: predatory) A creature that preys on other animals for most or all of its food.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

Texas     The second largest state in the United States, located along the southern border with Mexico. It is about 1,270 kilometers (790 miles) long and covers an area of 696,000 square kilometers (268,581 square miles).

Further Reading

Broadcom MASTERS awards $100,000 in prizes at 2016 national middle school STEM competition.” Society for Science & the Public press release. November 1, 2016.

Visit the Broadcom MASTERS homepage at SSP.