Q14 Dynamics Lab

A runnable three.js quadruped playground backed by hand-written spatial rigid-body dynamics, with a trained sensor-driven trot, 40 movable gravel rocks and experimental 3D particle water.

Trained trot on loose gravel (40 dynamic rocks)	Experimental SPH water
mp4 · physics ran at 0.17x real time; GIF sped up 5x	mp4 · 0.16x real time; GIF sped up 5x

Flat-ground trot with the footprint overlay, real time (1.01x)
mp4 · every link pose comes from the physics Worker; the renderer adds no animation

Results

Walking (sensor-only CPG/IK gait parameters from cross-entropy search; VALIDATION.md):

scene	duration	travelled	notes
flat, 3 held-out sensor-noise seeds	5 s	0.99568 / 0.99483 / 0.99436 m	all upright
gravel, 40 rocks, clearance 0.075 m	10 s	1.132 m	upright; min height 0.3372 m, max penetration 1.33 mm
water (flat-trained policy, no water training)	10 s	1.9087 m	upright; max density 19.7% above reference

Physics checks (named fixtures only):

check	measurement
double pendulum, 60 s, semi-implicit Euler	max relative energy drift 0.0191165%
ABA vs independent dense solve	absolute agreement <1e-10
determinism, pinned fixture	bit-identical states over 10,000 steps
gravel step runtime	9.89 ms per outer step: the 1 ms real-time target is not met

Quick start

npm install
npm run dev     # open http://localhost:5173 (Vite supplies the COOP/COEP headers; index.html directly will not work)
npm test
npm run build

More

• docs/USAGE.md: demo capture details, controls (gravel, water, impulses, gains, overlays) and checks.
• docs/COVERAGE.md: what is implemented (dynamics, contact, gravel world, walking policy, water) and what is outstanding.
• PHYSICS.md: implemented equations; VALIDATION.md: all measured results and limitations; BUILD_REQUEST.md: the full simulator specification.

Known limitations: not yet the complete simulator in BUILD_REQUEST.md; the SPH water is visibly compressible and not validated CFD; only straight trot on flat ground and gravel has walking validation.