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A Hoberman sphere is an
isokinetic Muscle contraction is the activation of tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as ...
structure patented by Chuck Hoberman that resembles a
geodesic dome A geodesic dome is a hemispherical thin-shell structure (lattice-shell) based on a geodesic polyhedron. The triangular elements of the dome are structurally rigid and distribute the structural stress throughout the structure, making geodesic dom ...
, but is capable of folding down to a fraction of its normal size by the
scissor Scissors are hand-operated shearing tools. A pair of scissors consists of a pair of metal blades pivoted so that the sharpened edges slide against each other when the handles (bows) opposite to the pivot are closed. Scissors are used for cutti ...
-like action of its joints. Colorful plastic versions have become popular as children's toys: several toy sizes exist, with the original design capable of expanding from in diameter to .


Description

A Hoberman sphere typically consists of six
great circle In mathematics, a great circle or orthodrome is the circular intersection of a sphere and a plane passing through the sphere's center point. Any arc of a great circle is a geodesic of the sphere, so that great circles in spherical geomet ...
s corresponding to the edges of an
icosidodecahedron In geometry, an icosidodecahedron is a polyhedron with twenty (''icosi'') triangular faces and twelve (''dodeca'') pentagonal faces. An icosidodecahedron has 30 identical vertices, with two triangles and two pentagons meeting at each, and 60 id ...
. The Hoberman sphere can be unfolded by allowing certain members to spread apart. The operation of each joint is linked to all the others in a
scissors mechanism A scissors mechanism uses linked, folding supports in a criss-cross 'X' pattern. Workings Extension is achieved by applying pressure to the outside of a set of supports located at one end of the mechanism, elongating the crossing pattern. This ...
like those used to mount
pantograph A pantograph (, from their original use for copying writing) is a mechanical linkage connected in a manner based on parallelograms so that the movement of one pen, in tracing an image, produces identical movements in a second pen. If a line dr ...
mirrors, or how a
folding chair A folding chair is a type of folding furniture, a light, portable chair that folds flat or to a smaller size, and can be stored in a stack, in a row, or on a cart. It can be combined with a folding table. Uses Folding chairs are generally used f ...
operates. In larger models, this can be accomplished by feeding out a string or cable instead. The largest existing Hoberman sphere is in the
AHHAA Science Centre AHHAA (Estonian language, Estonian: ''Teaduskeskus AHHAA'') is a science centre located in Tartu, Estonia, and is currently the largest science centre in the Baltic states. AHHAA was established to promote science and technology ...
Science Center in
Tartu, Estonia Tartu is the second largest city in Estonia after the Northern European country's political and financial capital, Tallinn. Tartu has a population of 91,407 (as of 2021). It is southeast of Tallinn and 245 kilometres (152 miles) northeast o ...
. Fully expanded, it is in diameter. The motorized sphere weighs , is constructed of aircraft-grade aluminum, and continually oscillates between its compact and expanded states. The sphere is suspended above the Center's Science Court and is actuated with a computer-based motion control system. This system opens and closes the sphere in a programmed series of lyrical motions choreographed to music, lighting and special effects. An earlier, similar but slightly smaller Hoberman sphere is in the atrium of
Liberty Science Center Liberty Science Center is an interactive science museum and learning center located in Liberty State Park in Jersey City, New Jersey, United States. At its opening it was the largest such planetarium in the Western Hemisphere and the world's ...
in
Jersey City, New Jersey Jersey City is the second-most populous city in the U.S. state of New Jersey, after Newark.Swiss Science Center Technorama in Winterthur, Switzerland.


See also

*
Hoberman mechanism A Hoberman mechanism, or Hoberman linkage, is a deployable mechanism that turns linear motion into radial motion. The Hoberman mechanism is made of two angulated ridged bars connected at a central point by a revolute joint, making it move much lik ...


References

{{Reflist


Further reading

* Greg Lynn (2014), ''Expanding sphere'', Canadian Centre for Architecture


External links


Hoberman.com - Welcome to the World of Magical Transformation

"Radial expansion/retraction truss structures"
Google Patents Google Patents is a search engine from Google that indexes patents and patent applications. Contents Google Patents indexes more than 87 million patents and patent applications with full text from 17 patent offices, including: * United States P ...

how to make a K'nex Hoberman sphere

How to make a popsicle Hoberman sphere
Linkages (mechanical) Polyhedra Educational toys