The primary illusion of movement is maybe best represented by a ribbon. Think of the '2001' Discovery spaceship centrifuge: it allowed unobstructed movement along the Z–axis (forward––backward). Since a human being looks left and right by turning his head, the ribbon is thus extended to a plane along the X–axis xi. Finally, up and down movement (along the Y–axis) extends the plane to a sphere, establishing an environment which completely envelops the user.
A good virtual reality interface therefore presupposes a virtual environment in which the participant can move around unobstructedly without ever running into a dead end in the corresponding actual reality; a kind of static mobility or, in other words, movement–in–one–place. However, the VR Ball interface has to be so spacious that even jumps and falls are possible.
The logical solution for such a 'static mobility' should therefore be an endless virtual plane, guaranteeing movement along 2 axes and represented by an actual sphere xii intersecting that plane in such a way that the participant is standing inside the sphere (or maybe an endless virtual plane intersecting the actual sphere in such a way that the participant is standing on top of the sphere).
This sphere is made of a porous synthetic material and rests on four magnetic bearings: one at the top (in case the participant is standing inside the sphere); and the others at the three corners of an equilateral triangle in the horizontal plane at such a distance from each other that the four bearings together form a tetrahedron (standing on top of the sphere the tetrahedron would be upside down). This enables movements along the X–, Y– and Z–axes.
By coherently varying the strength of the magnetic fields of all four bearings, movements along the Y–axis can be effected, similar to minute but sudden dislocations along the Y–axis in flight simulators. The sphere can be entered through a 'door' that can be closed in such a way that the seam cannot be located. Sufficient ventilation is at all times insured, however.
The radius of the sphere is such that, walking with eyes closed, one gets the illusion of walking on a flat plane. Through his actions the participant determines the displacement along the X– and Z–axis, whereas the displacement along the Y–axis depends on the currently valid VR.
The visual interface is effectuated by a 'no–glasses' stereoscopic background projection on the outside of the VR Ball, while the auditory and tactile interface is realized through the use of the more orthodox binaural headset and DataGloves. These are wireless, guaranteeing full freedom of movement for the participant.
The interface should be a combination of a DataSuit and a stringpuppet 'harness': the strings enable controlled movement (re: 60s NASA moonwalker simulator) along the Y–axis (in other words zero–gravity), while the DataSuit offers counterforce to the joints in the X– and Z–axis (in other words mass and weight).
Take it one step further and the strings should extend both ways: up and down, extending the Y–plane. Take it another step further and a person dons a suit at all joints attached to a 3–way cable–controlled force–feedback interface (cables at the larger ones, gloves etc. at the smaller ones). Combine this with the proposed no–glasses 3D interface on a globe. The whole setup should be able to create a powerful sensation of weightlessness.