Spider Kinematics and Dynamics

Agile legged motion on a miniature scale

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1. A New Zealand hunting spider, Dolomedes aquaticus.  They seem to be too small to exploit the same passive dynamic mechanisms that legged vertebrates use- which rely on the mass and inertia of the legs - and yet they are fast, efficient agile pursuit predators.

2. In physics-based computer models of legged locomotion at the scale of insects and spiders we can't reproduce the smooth, fluid motion of the real animals.   Agile control of a multi-link structure like this is too hard for a computer ... but it also seems to be too hard for a spider's brain.  So we think that the spider must be mechanically designed to make gait generation a much simpler problem.  What is it about the way that spiders are put together that allows them to move so gracefully, and be controlled so easily by a brain smaller than a pinhead?

3. MSc student Kiri Pullar is using a technique called model-based Bayesian inference to determine how spiders move.  This "markerless motion capture" technique compares images generated by a computer model of a spider to images from high-speed video of real spiders.  Starting with simple 2D stick-figure kinematic models (above), Kiri calculates how the joints move. This helps to design better spider models, and the better models are used to generate better estimates of how the joints move ... and so it goes, until in the end we hope to understand (and be able to reproduce in computer models and real robots) how spiders move.

4. MSc student Stefan Reussensehn is studying the mechanical design of the legs of Dolomedes aquaticus.  This video shows how legs are extended by fluid pressure and flexed by elastic plates at the joints.  We think that spiders may capture and recycle energy in elastic fluid resevoirs, making passive dynamic legged locomotion possible at this small scale.