# Big Brother and Sister

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Picture copyright by
PhotoArt Studio HĂ¶rby
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These models were built in 2022 and their maximum dimensions are 13.5 cm x 13.5
cm x 13.5 cm for big brother and 13 cm x 13 cm x 13 cm for big sister.
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These polyhedra consist of regular heptagons that are allowed to be folded over
diagonals. There are different ways in which you can fold a regular heptagon and
for these polyhedra the folding is done in a 'W' shape.
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Both polyhedra are quite similar and quite different at the same time.
Around one type of symmetry axis the heptagons are arranged around the regular
pentagons or triangles as a dish, while for the other type of symmetry axis they
are aranged as a propeller. In both the models the role of the axes are
exchanged.
These models have the rotational symmetries from a dodecahedron (or icosahedron).
A same kind of pair can be found for the cube (or octahedron) symmetry.
Models of those can be found
here.
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These models were quite hard to glue together. I built big sister first. Halfway
it was already getting hard and I thought that it would be even harder to
finish, but closer to the end it became easier instead. Big brother went a lot
easier when I was halfway and I thought it would be the easier model, but
towards the end there was quite some tension that made the model collapse a bit
and it became really hard in the end. To solve the problem I prepared a pentagon
with five triangles attached already while leaving gaps for the last five
isosceles triangles. This way I could straighten out the model through those 5
gaps, while gluing on the part with six pieces. That turned out to be a good
strategy. In the end this was one of the hardest models models I built.
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I think they both have a pleasing shape and they form a nice pair.
The choice of which one is brother and which one sister is based on the
following:
the propeller with three blades reminds me of a Y chromosome (brother) while for
little sister there are four which reminds me of an X chromosome (sister).
For big sister there are five, which means that big sister would be kind of a super woman.
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## Last Updated

2022-07-16