Theo Jansen's leg is a single-degree-of-freedom 12-bar linkage: one rotating crank (length m = 15) turns around a fixed pivot, and a second fixed pivot sits nearby, offset by the frame's own a and l dimensions (38.0, 7.8). From those two fixed points, links b through k (41.5, 39.3, 40.1, 55.8, 39.4, 36.7, 65.7, 49.0, 50.0, 61.9) chain together through a sequence of two-bar-per-joint triangulations, each new joint fixed relative to two already-known points — exactly like solving a jigsaw of overlapping circles.
Jansen found these eleven proportions with a genetic algorithm, evaluating thousands of candidate lengths against one fitness function: how flat the foot's path stays while it's "on the ground." The result is the famous Jansen curve — a smooth, almost circular arc during the swing phase, flattening sharply into a near-straight stride during ground contact, so the body glides forward at constant height without the up-down bob a simple rotating leg would cause.
A real Strandbeest mounts several of these legs on the same crankshaft, each pair offset in phase, so that at any instant some legs are mid-stride while others are lifting or planting — the overlap is what turns one twitchy linkage into a smooth, continuous walking gait.