Interactive Strandbeest math demo

Drag the crank, animate the linkage, and mutate the “holy number” rods. The demo constructs each moving joint with circle intersections, so the math stays visible while the foot traces its walking curve.

Strandbeests are kinetic beasts by Theo Jansen. Learn more at strandbeest.com and Theo Jansen on Wikipedia.

linkage solved Tip: drag anywhere on the canvas to set the crank angle

The circle-intersection math

Each unknown joint is found from two already-known joints and two rod lengths. For centers P and Q, radii r and s:

d = ||Q − P||
α = (r² − s² + d²) / (2d)
M = P + α(Q − P)/d
h = √(r² − α²)
intersection = M ± h · perpendicular((Q − P)/d)

The two signs give the two possible triangle orientations. This demo follows the Strandbeest branch by choosing W upward, V leftward, then U, T, and S downward.

Live construction checks

Canonical lengths used here

The values are dimensionless proportions. Scaling them all together makes a larger or smaller leg with the same foot path shape.

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