In 1992, the American artist, engineer, and architect Chuck Hoberman designed the “Expanding Sphere” for the Liberty Science Center in New Jersey. The isokinetic structure, which is still on show in New Jersey (and remains the world’s second largest), resembles a geodesic dome, but one that can fold down to a fraction of its original size thanks to the scissor-like action of the joints within it.
Seven years later, in 1992, Hoberman decided to mass produce his sphere as a children’s toy. Made of colorful plastic pieces, the Hoberman Sphere, as it was called, went on to sell in the millions, introducing kids to a fun object originally designed as an innovative example of structural engineering.
Today, Hoebrman Spheres hang in various science and technology centers across the world, including in Germany, Switzerland, South Korea, and Japan. But none are larger than the expanding sphere that hangs in Tartu’s AHHAA Science Center.
Made from aircraft-grade aluminum, this Hoberman Sphere expands from 4.9 to 19.4 feet (1.5 to 5.9 meters) in diameter in about three seconds. The structure weighs 750 pounds (340 kilograms) and is formed of 244 hubs and 1,440 linkages connected by 2,880 pins and 5,760 bearings.
The extension and folding of the sphere is controlled by two actuator cables that alternately pull the sphere’s opposing polar hubs. This creates the seemingly organic expansion and contraction of the sphere, its behavior demonstrating the concept of biomimicry, as can be seen in this short video.
Know Before You Go
The world’s largest Hoberman Sphere is suspended from the centrally-located domed atrium in the AHHAA Science Center in Tartu, the second largest city in Estonia. Tickets for the science center cost €13 ($14.75) for adults and €10 ($11.35) for school/university students and seniors. The center is open Sunday to Thursday from 10 a.m. to 7 p.m., and Friday and Sat from 10 a.m. to 8 p.m.