Spinning Box

Here is a basic example of building a simulation using newton.

import matplotlib.pyplot as plt
import newton
import numpy as np
import warp as wp
from lwmr.utils import RECORDING_BASE_PATH, create_viewer_viser
from tqdm.auto import trange

# Tell warp to be quiet before initializing a model
wp.config.quiet = True

/Users/ajcd2020/Documents/Repositories/anthonyjclark/simer-tutorial/2026-icra/.venv/lib/python3.14/site-packages/tqdm/auto.py:21: TqdmWarning: IProgress not found. Please update jupyter and ipywidgets. See https://ipywidgets.readthedocs.io/en/stable/user_install.html
  from .autonotebook import tqdm as notebook_tqdm

# Visualization timing
FRAME_STEP = 1.0 / 60.0

# Simulation timing relative to visualization
SIM_SUBSTEPS = 4
TIME_STEP = FRAME_STEP / SIM_SUBSTEPS

# Build a model
builder = newton.ModelBuilder()
body = builder.add_body()
builder.add_shape_box(body)
builder.add_ground_plane()
model = builder.finalize()

# Allocate state and create a solver
state_0 = model.state()
state_1 = model.state()
control = model.control()
contacts = model.contacts()
solver = newton.solvers.SolverMuJoCo(model)

# Step the simulation
for step in trange(1000):
    state_0.clear_forces()
    model.collide(state_0, contacts)
    solver.step(state_0, state_1, control, contacts, TIME_STEP)
    state_0, state_1 = state_1, state_0

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Visualization

We’ll use the built-in support for the viser visualizer in newton.

sim_time = 0.0

rec_path = str(RECORDING_BASE_PATH / "cube.viser")
viewer = newton.viewer.ViewerViser(verbose=False, record_to_viser=rec_path)
viewer.set_model(model)

while sim_time < 4.0:
    viewer.begin_frame(sim_time)
    viewer.log_state(state_0)
    viewer.end_frame()
    sim_time += FRAME_STEP

# NOTE: this does not work in VSCode
viewer.show_notebook()

╭────── viser (listening *:8080) ───────╮
│             ╷                         │
│   HTTP      │ http://localhost:8080   │
│   Websocket │ ws://localhost:8080     │
│             ╵                         │
╰───────────────────────────────────────╯

Visualize a Spinning Cube

add_body() calls add_link(), add_joint_free(), and add_articulation()

builder = newton.ModelBuilder()
builder.add_ground_plane()

# Revolute body
xform = wp.transform(p=wp.vec3(0.0, -1.0, 1.0))
body = builder.add_link()
joint = builder.add_joint_revolute(parent=-1, child=body, parent_xform=xform, axis=wp.vec3(0.0, 0.0, 1.0))
builder.add_articulation([joint])
builder.add_shape_box(body)

# Just a single DOF for a revolute joint
joint_index = builder.joint_q_start[joint]
joint_dim = builder.joint_dof_dim[joint_index]
assert joint_dim[0] == 0 and joint_dim[1] == 1
builder.joint_q[joint_index] = 0.5

joint_index = builder.joint_qd_start[joint]
joint_dim = builder.joint_dof_dim[joint_index]
assert joint_dim[0] == 0 and joint_dim[1] == 1
builder.joint_qd[joint_index] = 10.0

# Free body
xform = wp.transform(p=wp.vec3(0.0, 1.0, 1.0))
body = builder.add_body(xform=xform)
builder.add_shape_box(body)

joint_index = builder.joint_q_start[joint] + 1
joint_dim = builder.joint_dof_dim[joint_index]
assert joint_dim[0] == 3 and joint_dim[1] == 3
# builder.joint_q[joint_index + 2] = 0.5

joint_index = builder.joint_qd_start[joint] + 1
joint_dim = builder.joint_dof_dim[joint_index]
assert joint_dim[0] == 3 and joint_dim[1] == 3
builder.joint_qd[joint_index + 5] = 10.0

model = builder.finalize()

state_0 = model.state()
state_1 = model.state()
control = model.control()
contacts = model.contacts()

solver = newton.solvers.SolverMuJoCo(model)

sim_time = 0.0

viewer = create_viewer_viser("spinning_cube", model, quiet=False, overwrite=False)

for step in trange(200):
    for substep in range(SIM_SUBSTEPS):
        state_0.clear_forces()
        model.collide(state_0, contacts)
        solver.step(state_0, state_1, control, contacts, TIME_STEP)
        state_0, state_1 = state_1, state_0

    viewer.begin_frame(sim_time)
    viewer.log_state(state_0)
    viewer.end_frame()

    sim_time += FRAME_STEP

viewer.show_notebook()

Recording to docs/_static/spinning_cube.viser...

╭────── viser (listening *:8081) ───────╮
│             ╷                         │
│   HTTP      │ http://localhost:8081   │
│   Websocket │ ws://localhost:8081     │
│             ╵                         │
╰───────────────────────────────────────╯

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builder = newton.ModelBuilder()
builder.add_ground_plane()

# Revolute body
xform = wp.transform(p=wp.vec3(0.0, -1.0, 1.0))
body = builder.add_link()
joint = builder.add_joint_revolute(parent=-1, child=body, parent_xform=xform, axis=wp.vec3(0.0, 0.0, 1.0))
builder.add_articulation([joint])
builder.add_shape_box(body)

# Free body
xform = wp.transform(p=wp.vec3(0.0, 1.0, 1.0))
body = builder.add_body(xform=xform, mass=1.0)
builder.add_shape_box(body)

model = builder.finalize()

state_0 = model.state()
state_1 = model.state()
control = model.control()
contacts = model.contacts()

solver = newton.solvers.SolverMuJoCo(model)

joint_forces = np.zeros(control.joint_f.shape, dtype=np.float32)  # type: ignore
joint_index = builder.joint_qd_start[joint]
joint_forces[joint_index] = 100

joint_index = builder.joint_qd_start[joint] + 1
# joint_forces[joint_index + 0] = -10000.0
joint_forces[joint_index + 5] = -5000.0

control.joint_f.assign(joint_forces)  # type: ignore

sim_time = 0.0

# viewer = create_viewer("spinning_cube", model)
viewer = create_viewer_viser("spinning_cube", model, quiet=False, overwrite=False)


for step in trange(200):
    for substep in range(SIM_SUBSTEPS):
        state_0.clear_forces()
        model.collide(state_0, contacts)
        solver.step(state_0, state_1, control, contacts, TIME_STEP)
        state_0, state_1 = state_1, state_0

    viewer.begin_frame(sim_time)
    viewer.log_state(state_0)
    viewer.end_frame()

    sim_time += FRAME_STEP

viewer.show_notebook()

Recording to docs/_static/spinning_cube_01.viser...

╭────── viser (listening *:8083) ───────╮
│             ╷                         │
│   HTTP      │ http://localhost:8083   │
│   Websocket │ ws://localhost:8083     │
│             ╵                         │
╰───────────────────────────────────────╯

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builder.plot_articulation()

builder = newton.ModelBuilder()
builder.add_ground_plane()

# Revolute body
xform = wp.transform(p=wp.vec3(0.0, -1.0, 1.0))
body = builder.add_link()
joint = builder.add_joint_revolute(
    parent=-1,
    child=body,
    parent_xform=xform,
    axis=wp.vec3(0.0, 0.0, 1.0),
    actuator_mode=newton.JointTargetMode.VELOCITY,
    target_kd=100,
)
builder.add_articulation([joint])
builder.add_shape_box(body)

model = builder.finalize()

state_0 = model.state()
state_1 = model.state()
control = model.control()
contacts = model.contacts()

solver = newton.solvers.SolverMuJoCo(model)

joint_target_vels = np.zeros(control.joint_target_vel.shape, dtype=np.float32)  # type: ignore
joint_index = builder.joint_qd_start[joint]
joint_target_vels[joint_index] = 8.0
control.joint_target_vel.assign(joint_target_vels)  # type: ignore

sim_time = 0.0

# viewer = create_viewer("spinning_cube", model)
viewer = create_viewer_viser("spinning_cube", model, quiet=False, overwrite=False)


vels = []

for step in trange(400):
    for substep in range(SIM_SUBSTEPS):
        state_0.clear_forces()
        model.collide(state_0, contacts)
        solver.step(state_0, state_1, control, contacts, TIME_STEP)
        state_0, state_1 = state_1, state_0

    viewer.begin_frame(sim_time)
    viewer.log_state(state_0)
    viewer.end_frame()

    vels.append(state_0.joint_qd.numpy().copy())  # type: ignore

    sim_time += FRAME_STEP

viewer.show_notebook()

Recording to docs/_static/spinning_cube_02.viser...

╭────── viser (listening *:8084) ───────╮
│             ╷                         │
│   HTTP      │ http://localhost:8084   │
│   Websocket │ ws://localhost:8084     │
│             ╵                         │
╰───────────────────────────────────────╯

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plt.plot(vels);