Construction Details
At each of the four vertices, three air cylinders are joined by a three-axis 180-degree hinge joint. These joints protect the cylinder shafts and bushings from ground strikes, and the flexible hinge material provides a soft, resilient foot against which the Tetrahedron can push. The volume of space enclosed by the tetrahedron can shrink to nearly zero (flat, or degenerate), and expand to 0.117 cubic units when all edges are one unit (inches, feet ...) long. The flat shape prevents practical inclusion of a gas source on the tetrahedron chassis. A button-box or computer control sends current to an electrically-actuated pneumatic valve bank, which actuates the cylinders to extend or retract.
The Prime Tetrahedron uses 1/2" diameter cylinders and is optimized for high speed and power-to-weight ratio. Its 1/8" I.D. hose provides adequate air flow and pressure to allow wild leaping behavior.
The Skinny Tetrahedron's 3/8" diameter cylinders and 1/16" I.D. hose optimize it for low gas usage and gentle motion; it is still surprisingly agile.
The Big Tetrahedron uses 3/4" diameter cylinders and isn't really optimized for anything except looming over children and animals. Pneumatic cylinder manufacturers only make cylinders this long and skinny under protest, and offer absolutely no warranty for any use.
The Human Scale Tetrahedron (5’ – 10’ tall) is planned for completion for live performance. Its initial incarnation will be PVC Schedule 40 pipe with end travel dampeners and flow metering.
© Frank Hausman