Speed caps

Basics

Gold bodies have a fall-speed cap, a spin cap and spin damping.

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Loop

The steel preset (the default), recordedon an NVIDIA RTX PRO 6000 Blackwell.

Run it

cd examples
# the default preset (steel), then the others
uv run shelf play body_limits
# change solver settings live
uv run shelf tune body_limits

Source: examples/shelf/00_basics/body_limits/ · ported from steel-webgpu tools/scenes.py body_limits() @ ad03e49

Presets

Preset	Solver	Status	Checked
steeldefault	steel	works	2026-11-10, newton f6fc82a8b, NVIDIA RTX PRO 6000 Blackwell Server Edition
xpbd	xpbd	unsupported	the gold bodies use Steel's steel:rigid_body_* attributes
vbd	vbd	unsupported	the gold bodies use Steel's steel:rigid_body_* attributes
mujoco	mujoco	unsupported	the gold bodies use Steel's steel:rigid_body_* attributes
featherstone	featherstone	unsupported	the gold bodies use Steel's steel:rigid_body_* attributes
semi_implicit	semi_implicit	unsupported	the gold bodies use Steel's steel:rigid_body_* attributes
feather_pgs	feather_pgs	unsupported	the gold bodies use Steel's steel:rigid_body_* attributes
kamino	kamino	unsupported	the gold bodies use Steel's steel:rigid_body_* attributes
implicit_mpm	implicit_mpm	unsupported	the gold bodies use Steel's steel:rigid_body_* attributes
style3d	style3d	unsupported	the gold bodies use Steel's steel:rigid_body_* attributes

Solvers with no row are untested on this example. The full settings are inpresets.toml.

Code

example.py

examples/shelf/00_basics/body_limits/example.py

# SPDX-FileCopyrightText: Copyright (c) 2026 Skild AI and the Steel contributors
# SPDX-License-Identifier: Apache-2.0
# Direct source: steel-webgpu; see presets.toml and THIRD_PARTY.md.
# Modified for Steel Shelf: preset-driven execution and shared runner integration.

###########################################################################
# Example Speed caps
#
# Steel's per-body attributes: max linear velocity, max angular velocity and angular damping.
#
# Ported from steel-webgpu's tools/scenes.py (body_limits); the scene builds
# as it does there and the shelf's preset drives the solver.
#
# Command: python -m shelf run body_limits
#
###########################################################################

import math

import numpy as np
import warp as wp

import newton
import newton.examples
from common.steel_scenes import BLUE, GOLD, GREY, RED, TEAL, SceneExample, cfg, tf


class Example(SceneExample):
    file = __file__
    camera = {'eye': (0.0, -2.0, 1.0), 'target': (0.0, 0.0, 0.3)}

    def build(self):
        """Steel's per-body attributes: max linear velocity, max angular velocity and angular damping."""
        b = newton.ModelBuilder()
        newton.solvers.SolverSteel.register_custom_attributes(b)
        b.add_ground_plane(cfg=cfg(mu=0.0))
        twists = {}
        rows = (
            ("max linear velocity 1 m/s", {"steel:rigid_body_max_linear_velocity": 1.0}, (0.0, 0.0, 0.0, 0.0, 0.0, 0.0), 1.6),
            ("max angular velocity 5 rad/s", {"steel:rigid_body_max_angular_velocity": 5.0}, (0.0, 0.0, 0.0, 0.0, 0.0, 30.0), 0.3),
            ("angular damping 2 /s", {"steel:rigid_body_angular_damping": 2.0}, (0.0, 0.0, 0.0, 0.0, 0.0, 30.0), 0.3),
        )
        for i, (_, custom, tw, z) in enumerate(rows):
            for k, limited in enumerate((False, True)):
                body = b.add_body(xform=tf((-0.4 + 0.4 * i, -0.15 + 0.3 * k, z)), custom_attributes=custom if limited else None)
                b.add_shape_box(body, hx=0.05, hy=0.05, hz=0.05, cfg=cfg(density=500, mu=0.0), color=[GREY, GOLD][k])
                twists[body] = tw
        return b, twists, "Per-body limits (gold vs grey): a 1 m/s fall cap, a 5 rad/s spin cap and 2 /s angular damping on frictionless spinners."

    def check(self):
        """At the end of the test run (100 frames): the twists reached the spinners and each gold limit acts."""
        w = np.abs(self.state_0.body_qd.numpy()[:, 5])
        # bodies: (grey, gold) per row; rows: fall cap, spin cap, angular damping
        assert w[2] > 25.0 and w[4] > 25.0, f"the grey spinners lost their 30 rad/s twist: {w[[2, 4]]}"
        assert 4.0 < w[3] <= 5.05, f"the spin-capped box spins at {w[3]:.3f} rad/s, not at its 5 rad/s cap"
        assert w[5] < 0.1 * w[4], f"the damped spinner still spins at {w[5]:.3f} rad/s"


if __name__ == "__main__":
    parser = Example.create_parser()
    viewer, args = newton.examples.init(parser)
    newton.examples.run(Example(viewer, args), args)

example.py on GitHub

presets.toml

examples/shelf/00_basics/body_limits/presets.toml

example = "body_limits"
source = "steel-webgpu tools/scenes.py body_limits() @ ad03e49"
default = "steel"

[check]
# Arguments `python -m shelf check` passes in test mode.
args = []

[gallery]
short = "Gold bodies have a fall-speed cap, a spin cap and spin damping."
title = "Speed caps"
frame = 90

[xpbd]
status = "unsupported"
reason = "the gold bodies use Steel's steel:rigid_body_* attributes"

[vbd]
status = "unsupported"
reason = "the gold bodies use Steel's steel:rigid_body_* attributes"

[mujoco]
status = "unsupported"
reason = "the gold bodies use Steel's steel:rigid_body_* attributes"

[featherstone]
status = "unsupported"
reason = "the gold bodies use Steel's steel:rigid_body_* attributes"

[semi_implicit]
status = "unsupported"
reason = "the gold bodies use Steel's steel:rigid_body_* attributes"

[feather_pgs]
status = "unsupported"
reason = "the gold bodies use Steel's steel:rigid_body_* attributes"

[steel]
status = "works"
# 1 substep x 2 iterations, immediate response: the gold caps act exactly as with 16 x 32 (fall capped at 1.000 m/s,
# spin at 4.996 rad/s; the damped spinner decays as w *= 1 - 2 dt per step, 3.92 rad/s after 1 s vs 4.05 at 16
# substeps) and every box lands and rests (0.3 mm peak penetration). 1 x 1 rests 0.7 mm deep. Free bodies only, so
# the immediate response (0.30 ms) does what propagation_colored did (0.39 ms); no joint has limits, so they are off.
# The port's 4 x 12 colored with limits: 2.43 ms.
sim = { fps = 60, substeps = 1 }
solver = { solve_mode = "matrix_free", iterations = 2, articulated_contact_response = "immediate", enable_joint_limits = false }
checked = "2026-11-10, newton f6fc82a8b, NVIDIA RTX PRO 6000 Blackwell Server Edition"

[kamino]
status = "unsupported"
reason = "the gold bodies use Steel's steel:rigid_body_* attributes"

[implicit_mpm]
status = "unsupported"
reason = "the gold bodies use Steel's steel:rigid_body_* attributes"

[style3d]
status = "unsupported"
reason = "the gold bodies use Steel's steel:rigid_body_* attributes"

presets.toml on GitHub

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