Joint speed limits

Basics

Two double pendulums; the gold one has a speed limit.

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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 vel_limit
# change solver settings live
uv run shelf tune vel_limit

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

Presets

Preset	Solver	Status	Checked
steeldefault	steel	works	2026-11-10, newton f6fc82a8b, NVIDIA RTX PRO 6000 Blackwell Server Edition

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

Code

example.py

examples/shelf/00_basics/vel_limit/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 Joint speed limits
#
# Joint velocity limits: two double pendulums released horizontal; the gold one has |qd| <= 1.5 rad/s.
#
# Ported from steel-webgpu's tools/scenes.py (vel_limit); the scene builds
# as it does there and the shelf's preset drives the solver.
#
# Command: python -m shelf run vel_limit
#
###########################################################################

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': (0.3, -2.0, 1.1), 'target': (0.3, 0.0, 0.55)}

    def build(self):
        """Joint velocity limits: two double pendulums released horizontal; the gold one has |qd| <= 1.5 rad/s."""
        b = newton.ModelBuilder()
        b.add_ground_plane()
        for y, vmax, color in ((0.25, 1e6, GREY), (-0.25, 1.5, GOLD)):
            prev, joints = -1, []
            for k in range(2):
                link = b.add_link(xform=tf((0.15 + 0.3 * k, y, 0.8)))
                b.add_shape_capsule(link, xform=tf(q=wp.quat_rpy(0.0, math.pi / 2, 0.0)), radius=0.03, half_height=0.12,
                                    cfg=cfg(density=800), color=color)
                parent_xform = tf((0, y, 0.8)) if prev < 0 else tf((0.15, 0, 0))
                joints.append(b.add_joint_revolute(prev, link, parent_xform=parent_xform, child_xform=tf((-0.15, 0, 0)),
                                                   axis=(0, 1, 0), velocity_limit=vmax))
                prev = link
            b.add_articulation(joints)
        return b, {}, "Velocity limits: the grey double pendulum swings freely; the gold one is held to 1.5 rad/s per joint.", {}

    def check(self):
        """The gold joints stay at or below their 1.5 rad/s limit."""
        qd = np.abs(self.state_0.joint_qd.numpy())
        assert qd[2:].max() <= 1.5 * 1.05, f"a gold joint moves at {qd[2:].max():.3f} rad/s, over its 1.5 rad/s limit"


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/vel_limit/presets.toml

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

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

[gallery]
short = "Two double pendulums; the gold one has a speed limit."
title = "Joint speed limits"
frame = 90

[xpbd]
status = "untested"

[vbd]
status = "untested"

[mujoco]
status = "untested"

[featherstone]
status = "untested"

[semi_implicit]
status = "untested"

[feather_pgs]
status = "untested"

[steel]
status = "works"
# 6 substeps x 4 iterations, immediate response: the gold joints peak at 1.518 rad/s against their 1.5 limit (4 x 4:
# 1.528, 1 x 2: 1.668) and the grey double pendulum follows a 16 x 32 run within 6 mm through its first second
# (4 substeps: 10 mm, 1: 69 mm; past that the chaotic grey pendulum diverges at any step size). Its energy error
# shrinks with the substep (1 substep gains 0.9 J of its 3.7 J swing in the first second, 4 gain 0.21 J, 6 gain 0.14 J).
# Iterations only tighten the velocity limit; no joint has position limits, so they are off; no contacts, so the
# immediate response (0.80 ms; 8 x 4 1.07 ms). The port's 4 x 12 colored: 2.00 ms.
sim = { fps = 60, substeps = 6 }
solver = { solve_mode = "matrix_free", iterations = 4, articulated_contact_response = "immediate", enable_joint_velocity_limits = true, enable_joint_limits = false }
checked = "2026-11-10, newton f6fc82a8b, NVIDIA RTX PRO 6000 Blackwell Server Edition"

[kamino]
status = "untested"

[implicit_mpm]
status = "untested"

[style3d]
status = "untested"

presets.toml on GitHub

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