Fairbanks sisters have built robots since they were toddlers. Now they’re competing on a world stage.

WASHINGTON – Colleen Johnson built her first robot at age 2, sitting on her father's lap. It was a "sumo" robot, designed to knock other automatons down. And it played the tune "Twinkle, Twinkle Little Star."

You know, child's play.

Johnson's younger sister, Katie, was not far behind. She soon made her own android, just "a tiny little thing that moved." The Johnson sisters, now 16 and 18, have been hooked ever since.

Now the Johnsons, who only recently moved from Fairbanks to Washington state, along with their co-captain Sanjna Ravichandar, 17, of New Jersey, make up Team USA for the inaugural FIRST Global Robotics Challenge, whose two days of game play take place Monday and Tuesday in Washington, D.C.

The three teens have spent the past several months not only building their own robot, but contacting teams from around the world to offer their assistance with everything from technical troubleshooting to dealing with the heat of a Washington summer.

"We feel like as the host country, it's our responsibility to make it a good experience for everyone," Ravichandar said at a hectic all-team practice session Saturday. She had just offered advice to some members of Team Botswana, whose robot had not arrived at the airport.

The competition, designed to promote Science, Technology, Engineering and Mathematics (STEM) around the world, will include a team from Afghanistan, which had initially been denied U.S. visas.

Other children play with dolls and toy cars. The Johnsons grew up tinkering with parts of old sewing machines and lawn mowers, which their parents, both trained as engineers, picked up from scrap yards in Fairbanks.

In the early 2000s, their parents, Tom and Sharon, began working as coaches, judges, and referees for FIRST (For Inspiration and Recognition of Science and Techology), a not-for-profit youth organization that runs several robotics competitions for elementary, middle and high school students. Almost soon as the girls were old enough to compete, they began participating in FIRST's Lego and tech challenges.

Their team, Schrodinger's Hat, formed with four other Fairbanks students, has participated in more than 20 competitions. (Its name comes from Erwin Schrodinger's famous thought experiment: The team competes wearing giant top hats decorated with cat's eyes). In 2015, the team won the FIRST Tech Challenge World Championship Inspire Award, the top award in the international competition.

According to the Johnsons, robotics are a surprisingly popular pastime in Fairbanks. ("It's dark and cold nine months of the year," Katie Johnson says with a shrug.) But even there, the Johnsons are known as the "robot girls."

The sisters have taken advantage of their reputation to promote STEM in their community, especially to young girls. As a young woman, "just one negative experience can turn you off STEM," Colleen Johnson said. "But knowing other women have experienced that, and have risen above it, is so inspiring."

Across the country in Princeton, New Jersey, Ravichandar was also a member of an all-girls team – actually, an all-Girl Scout team, called, fittingly, "We Are Girl Scouts (W.A.G.S.)." Their trademark? "Our branding is excessive amounts of purple, glitter, beads and neon hats," she said. The team has also competed in more than 20 competitions and won several awards.

Ravichandar met Colleen Johnson when both were both recognized on the FIRST Dean's List for outreach and leadership. For both girls, it was like meeting a celebrity: Each had followed the other's team on social media. After the Johnsons were tapped to represent the United States at FIRST Global, they asked Ravichandar to join.

"I didn't believe it was real," she gushed.

On the Saturday before the competition, the Daughters of the American Revolution Constitution Hall is packed with teenagers wearing T-shirts and buttons emblazoned with national flags, carrying complicated mechanical contraptions over their heads. Team USA, crammed in a booth between Team Uganda and Team U.K., was doing some last-minute tinkering after a practice run that morning had revealed some problems with its robot's battery.

For the team, this is the culmination of months of designing, building and programming. As part of the inaugural Global Challenge, the competitors learn about challenges to accessing clean water for people around the world. The competition requires each team to build a robot that will sort "water particles" (represented by blue balls) from "contaminant particles" (represented by orange balls), depositing the former in a "village reservoir" and the latter in a "laboratory." Afterward, the robot must hang from a bar to avoid a "flood."

Working only with materials allotted in their official kits, the teams had to build mechanisms to collect the balls, sort them using a color sensor and deposit them in the correct locations. They also had to design a device to hang the robot during the flood portion of the game. Team USA worked on its design almost every day since March – at least three or four hours a day, and up to 12 in the last few weeks before the competition. Through the months-long design and building process, Ravichandar communicated with the Johnsons via Google HangOut, shared spreadsheets and text messages.

The girls also kept an engineering notebook, documenting their ideas and progress. Ravichandar wrote her entries on loose graphing paper. When the team members finally met in Washington in June, they all wrote in the notebook together for the first time.

Besides design ideas, the notebook also documents the girls' online meetings with teams from other countries. "I have also continued to talk with members of Team Rwanda, and have helped them with their robot," one entry reads. "A member of Team Tanzania began messaging me on Facebook," another reads. The Johnsons also acted as official mentors for Team Colombia.

Just a few minutes before Team USA is up to practice, Ravichandar runs over to her teammates, out of breath, reporting that Team Bahamas has had a technical problem. "But I think they're OK," she adds. "And their mechanism is so cool." When she describes it, Katie squeals.

"You can only use what's in the box," Ravichandar says, explaining why she's excited. "Each of those teams used those pieces to build a completely different robot."