Presets
Playback
Structure, load and environment
The struts only push, the cables only pull. Prestress pulls the cables taut so that the loaded structure keeps all of its cables carrying tension.
Model checks
The science
What is modelled
A tensegrity prism: three rigid struts join a fixed lower triangle to a movable upper triangle, and nine cables (three lower, three upper, three diagonal) hold it together. The cables carry tension only. The page runs the same fixed-step integrator as the 3D page, which treats the struts as inextensible by projection, and draws the result in two projected views.
Equations
- Cable tension
T = k (L - L0)when taut, zero when slack, plus a dashpot; rest lengthL0 = L_ref (1 - prestress). - Node dynamics
m a = sum(T n) + m g + wind, with velocity damping. - Strut rigidity by iterative projection
L_strut = const. - Energy
E = kinetic + sum(k s2 / 2) + m g y.
Checks run in the page
- Strut length deviation after a pluck.
- Static equilibrium: the part of the node force perpendicular to the strut must vanish.
- Energy bookkeeping with damping switched off.
- Linear response of the sag to small payloads.
Honest simplifications
A conceptual model: the struts have no mass or buckling limit, the cables are linear springs with a simple dashpot, the base is perfectly rigid, wind is a constant push on the upper nodes, and there is no friction or contact other than a floor stop. The tensions are illustrative and not a structural design check.
What to try
- Press Pluck and watch the top triangle ring down; raise the damping to calm it.
- Lower the prestress to zero and add payload to see cables go slack.
- Press Moon gravity: the structure sags less and rings for longer.