⚠️ Deprecation Notice: Starting with Newton 1.3, actuators are created in and used exclusively from Newton's built-in newton.actuators module. This standalone newton-actuators package will no longer be maintained. Please migrate:

• Concepts guide: https://newton-physics.github.io/newton/latest/concepts/actuators.html
• API reference: https://newton-physics.github.io/newton/latest/api/newton_actuators.html

Newton Actuators

GPU-accelerated actuator library for physics simulations.

This library provides a collection of actuator implementations that integrate with physics simulation pipelines. Actuators read from simulation state arrays and write computed forces/torques back to control arrays.

Installation

pip install newton-actuators

Or install from source:

cd newton-actuators
pip install -e .

With PyTorch (for neural network actuators)

The ActuatorNetMLP and ActuatorNetLSTM actuators require PyTorch. Install the extra matching your CUDA version:

Using uv (index routing is automatic):

uv pip install "newton-actuators[torch-cu12]"   # CUDA 12.x
uv pip install "newton-actuators[torch-cu13]"   # CUDA 13.x

Using pip (requires manual --extra-index-url):

pip install "newton-actuators[torch-cu12]" --extra-index-url https://download.pytorch.org/whl/cu128
pip install "newton-actuators[torch-cu13]" --extra-index-url https://download.pytorch.org/whl/cu130

API Reference

Actuator Classes

Actuator	Description	Stateful	Transmission
ActuatorPD	Stateless PD controller	No	No
ActuatorPID	PID controller with integral term	Yes	No
ActuatorDelayedPD	PD controller with input delay	Yes	No
ActuatorDCMotor	PD with DC motor velocity-dependent saturation	No	No
ActuatorRemotizedPD	Delayed PD with angle-dependent torque limits	Yes	No
ActuatorNetMLP	MLP network actuator with position/velocity history	Yes	No
ActuatorNetLSTM	LSTM network actuator with recurrent hidden state	Yes	No

Control Laws

• ActuatorPD: τ = clamp(constant + act + Kp·(target_pos - q) + Kd·(target_vel - v), ±max_force)
• ActuatorPID: τ = clamp(constant + act + Kp·(target_pos - q) + Ki·∫e·dt + Kd·(target_vel - v), ±max_force)
• ActuatorDelayedPD: Same as PD but with delayed targets (circular buffer)
• ActuatorDCMotor: Same PD force computation, but torque is clamped to velocity-dependent bounds from the motor torque-speed curve: τ_max(v) = clamp(τ_sat·(1 - v/v_max), 0, effort_limit), τ_min(v) = clamp(τ_sat·(-1 - v/v_max), -effort_limit, 0), τ = clamp(τ, τ_min(v), τ_max(v))
• ActuatorRemotizedPD: Same as DelayedPD, but torque limits are interpolated from an angle-dependent lookup table: τ_limit = interp(q, lookup_table)
• ActuatorNetMLP: τ = clamp(network(cat(pos_error_history * pos_scale, vel_history * vel_scale)) * torque_scale, ±max_force) — history is maintained internally
• ActuatorNetLSTM: τ = clamp(network(input, (h, c)), ±max_force) — hidden and cell state maintained internally

Base Class Methods

All actuators inherit from Actuator and provide these methods:

• resolve_arguments(args) -> dict: (classmethod) Resolve user-provided arguments with defaults
• is_stateful() -> bool: Returns True if the actuator maintains internal state
• is_graphable() -> bool: Returns True if step() can be captured in a CUDA graph (False for torch-based NN actuators)
• has_transmission() -> bool: Returns True if the actuator has a transmission phase
• state() -> State | None: Returns a new state instance (None for stateless actuators)
• step(sim_state, sim_control, current_state, next_state, dt): Execute one control step

State Classes

Stateful actuators use nested State classes:

• ActuatorPID.State - Contains the integral term for PID control

• ActuatorDelayedPD.State - Contains circular buffers for delayed targets

• ActuatorRemotizedPD.State - Inherits ActuatorDelayedPD.State (same delay buffers)

• ActuatorNetMLP.State - Contains position error and velocity history buffers

• ActuatorNetLSTM.State - Contains LSTM hidden and cell state tensors

Workflow

1. Create actuators with appropriate parameters
2. Check statefulness: Call actuator.is_stateful() to determine if state management is needed
3. Initialize states: For stateful actuators, create double-buffered states with actuator.state()
4. Simulation loop: Call actuator.step() to compute forces
5. Swap buffers: For stateful actuators, swap state buffers after each step
6. Reset between episodes: Call state.reset() on any stateful actuator's state to zero internal buffers without reallocating

Examples

Stateless Actuator (ActuatorPD)

import warp as wp
from newton_actuators import ActuatorPD

# Create a PD actuator for 3 DOFs
indices = wp.array([0, 1, 2], dtype=wp.uint32)
pd_actuator = ActuatorPD(
    input_indices=indices,
    output_indices=indices,
    kp=wp.array([100.0, 100.0, 100.0], dtype=wp.float32),
    kd=wp.array([10.0, 10.0, 10.0], dtype=wp.float32),
    max_force=wp.array([50.0, 50.0, 50.0], dtype=wp.float32),
    constant_force=wp.array([0.0, 0.0, 0.0], dtype=wp.float32),
)

# In simulation loop - stateless actuators don't need state management
pd_actuator.step(sim_state, sim_control, None, None, dt=0.01)

Stateful Actuator (ActuatorPID)

import warp as wp
from newton_actuators import ActuatorPID

indices = wp.array([0, 1], dtype=wp.uint32)
pid_actuator = ActuatorPID(
    input_indices=indices,
    output_indices=indices,
    kp=wp.array([100.0, 100.0], dtype=wp.float32),
    ki=wp.array([10.0, 10.0], dtype=wp.float32),
    kd=wp.array([5.0, 5.0], dtype=wp.float32),
    max_force=wp.array([50.0, 50.0], dtype=wp.float32),
    integral_max=wp.array([10.0, 10.0], dtype=wp.float32),
    constant_force=wp.array([0.0, 0.0], dtype=wp.float32),
)

# Check if actuator needs state management
if pid_actuator.is_stateful():
    # Create double-buffered states
    state_a = pid_actuator.state()
    state_b = pid_actuator.state()

# Simulation loop with state swapping
current_state, next_state = state_a, state_b
for step in range(num_steps):
    pid_actuator.step(sim_state, sim_control, current_state, next_state, dt=0.01)
    current_state, next_state = next_state, current_state  # Swap buffers

Non-Graphable Stateful Actuator (ActuatorNetLSTM)

Network actuators (ActuatorNetMLP, ActuatorNetLSTM) are stateful but not CUDA-graphable due to Warp-PyTorch interop. Because their step() cannot be captured in a CUDA graph, double-buffering is not strictly required — you can pass the same state object as both current_state and next_state:

# Simple: single state object (fine when not using CUDA graphs)
state = lstm_actuator.state()
for step in range(num_steps):
    lstm_actuator.step(sim_state, sim_control, state, state, dt=0.01)

USD Parsing

The library includes utilities for parsing actuator definitions from USD files:

from newton_actuators import parse_actuator_prim

# Parse a USD prim with actuator attributes
result = parse_actuator_prim(prim)
if result is not None:
    actuator_class = result.actuator_class  # e.g., ActuatorPD
    target_paths = result.target_paths      # e.g., ["/World/Robot/Joint1"]
    kwargs = result.kwargs                   # e.g., {"kp": 100.0, "kd": 10.0}

License

Apache-2.0