Kinetic sculpture simulation · field notes
Every joint of every leg is solved from circle–circle intersections, sixty times a second, from the thirteen lengths of the Jansen linkage.
drag the beach to pan · the wind drives the crank
Each leg is a planar linkage hung from one fixed pivot on the body and driven by a crank of radius m. Given the crank angle θ, the crank tip sits at (m·cos θ, m·sin θ). Every other joint is the meeting point of two links of known length, so it lies where two circles cross. The solver finds the upper joint from j and b, the knee from k and c, the outer corner of the upper triangle from e and d, the rear corner of the foot triangle from f and g, and finally the foot from h and i. Each time it keeps the one of the two crossings that matches the leg's assembly.
Pairs of legs are mirror images sharing a crank, and each pair runs at its own phase, so there is always a foot on the sand. The body is moved so that the foot in contact does not slip, and it settles to whatever height keeps that foot on the ground. The walk and the gentle bob come straight out of the geometry.
Inspired by the Strandbeesten, the wind-walking beach creatures the Dutch artist Theo Jansen has been building since 1990. This is an original rendering and simulation, not a model of any particular beest.
| a | crank axle to fixed pivot, horizontal | 38.0 |
|---|---|---|
| l | crank axle to fixed pivot, vertical | 7.8 |
| m | crank radius | 15.0 |
| j | crank to upper joint | 50.0 |
| k | crank to knee | 61.9 |
| b | pivot to upper joint | 41.5 |
| c | pivot to knee | 39.3 |
| d | pivot to outer corner (upper triangle) | 40.1 |
| e | upper joint to outer corner (upper triangle) | 55.8 |
| f | outer corner to rear corner | 39.4 |
| g | knee to rear corner (foot triangle) | 36.7 |
| h | rear corner to foot (foot triangle) | 65.7 |
| i | knee to foot (foot triangle) | 49.0 |