These are general instructions for making the Hoberman spheres.
I've designed several different part/kit versions (4 or 5) with
varying success. These instruction will guide you to the overall
assembly of the sphere. There will be other documentation on the
actually assembly of the parts in a given kit version.
This
design is based upon a star dome (icosidodecahedron). It has 60 edges
of the same length and 30 verticies. Each edge will be comprised of a
pair of curved arms joined together by a pivot joint at their
midpoints. Each vertex will be comprised of a pair of hubs (an inner
hub and an outer hub), each connected to 4 arms allowing pivotal
motion in the plane of the arm.
You will need:
60 pairs of
arms (120 arms)
60 sets of arm pivot point pins/fasteners
30
hub pairs (60 hubs) (if used)
240 sets of hub pins/fasteners (if
used)
The dome is made up of pentagons and triangles using the
arms as sides and the hubs as corners.
Every side of every
pentagon must also be the side of an adjacent triangle and
visa-versa.
Every pair of inner and outer hubs will be the
intersection of the corners of 2 pentagons and 2 triangles.
The
arms are pinned together in pairs through their middle holes.
Every
pair of arms goes between two sets of an inner and outer hub at both
ends of the arms.
A given arm will be connected to an inner
hub at one end and an outer hub at the other.
The curvature of
the arms goes towards the center of the dome.
The hubs are not
symmetrical - if you put a strait edge across a hub from where one
arm attaches, through the center of the hub, to the place where the
opposite arm attaches - you would see that the two arms across from
each other will attach on opposite sides of the strait edge.
The
pair of arms across from each other must always be attached to the
hubs such that one arm of each pair is on either side of the line
defined by the above mentioned strait edge.
To accomplish this
the inner and outer hubs of each hub pair must be flipped relative to
each other (opposites sides of a coin).
If you follow these
rules it will eventually form an expandable/collapsible geodesic
dome.
If you have any questions email me at
johann@fablab.no
Good
Luck,
Johann