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MuJoCo (Multi-Joint dynamics with Contact)

repository·main·Indexed 12 days ago

https://github.com/google-deepmind/mujoco

A high-performance physics engine for simulating articulated structures, widely used in robotics, biomechanics, machine learning, and computer graphics. Includes MuJoCo XLA (MJX), a JAX-based re-implementation (version 3.11.1), as well as support for PID actuator plugins, elasticity plugins, Signed Distance Function (SDF) implicit geometries, and specialized touch sensors.

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What's inside MuJoCo

  1. Overview of OpenUSD support in MuJoCo

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    MuJoCo provides experimental support for OpenUSD (Universal Scene Description), an open-source framework for describing 3D scenes. This integration allows MuJoCo users to leverage the USD ecosystem for interoperability with tools like Houdini, Maya, and Blender, and to utilize USD's rich scene description capabilities (geometry, materials, lighting, and hierarchies).

    Note: OpenUSD support is currently experimental and subject to frequent change.

  2. Overview of the Humanoid model

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    The Humanoid model is a simplified bipedal model designed for studying locomotion behaviors. This specific implementation is based on the model used in the DeepMind Control Suite, which features realistic actuator gains.

    Key specifications:

    • Degrees of Freedom (DoF): 27
    • Actuators: 21

  3. Overview of mjcPhysics for OpenUSD

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    mjcPhysics provides USD (Universal Scene Description) schemas designed to specify MuJoCo simulation environments directly within USD files.

    Key characteristics:

    • Extends, doesn't replace: It is designed to extend existing USD concepts (like UsdPhysics) rather than replacing them, creating new types only when necessary for MuJoCo-specific physics.
    • Compatibility: The schemas are compatible with any application that supports USD natively, including NVIDIA Omniverse, Houdini, and Maya.
    • Usage modes: You can use these schemas 'codeless' (directly within USD authoring tools) or via C++ bindings for programmatic control.

  4. Use the MuJoCo Unity Plug-in

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    The MuJoCo Unity plug-in enables the Unity Editor and runtime to utilize the MuJoCo physics engine. This allows you to import MJCF (MuJoCo XML) files directly into Unity and edit models within the Editor environment. While the plug-in leverages Unity for assets, game logic, and simulation time, it uses MuJoCo to calculate object movement, providing designers with access to the full MuJoCo API within the Unity ecosystem.

  5. Use the Simulate App for interactive MuJoCo visualization

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    The simulate application is an interactive tool for visualizing and interacting with MuJoCo simulations. It uses the GLFW library to open an OpenGL window to render the simulation state.

    Key features include:

    • Model Loading: Specify a model file as a command-line argument or load one at runtime by dragging and dropping a file into the window.
    • Built-in Tools: Access simulation statistics, a profiler, sensor data plots, and built-in help within the application.
    • Interactivity: Provides a fully-featured environment for inspecting simulation behavior visually.
    # Example usage (conceptual):
# Running simulate with a specific model file
./simulate my_model.xml

  7. Use mjcPhysics to specify MuJoCo environments in OpenUSD

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    The mjcPhysics schema allows you to define a MuJoCo simulation environment directly within a USD file. It is designed to extend existing OpenUSD physics concepts rather than replacing UsdPhysics.

    Note: OpenUSD support is currently experimental and subject to frequent change.

  8. MuJoCo XML Schema Overview

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    The MuJoCo XML schema defines the structure for model files used in simulations. The schema is organized into several high-level categories: model, option, compiler, size, statistic, and asset. These categories allow users to define physical properties, simulation parameters, compilation behaviors, memory limits, and external assets like meshes and textures.

  9. Overview of Elasticity plugins

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    MuJoCo provides first-party elasticity plugins that implement passive forces using discretized continuum mechanics models. These plugins can be applied to flexes or to bodies using the composite functionality. You can find sample models for these plugins in the model/plugin/elasticity/ directory of the repository.

  10. What is MuJoCo XLA (MJX)?

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    MuJoCo XLA (MJX) provides a JAX API for MuJoCo implementations, allowing simulations to run on hardware supported by the XLA compiler, including Nvidia and AMD GPUs, Apple Silicon, and Google Cloud TPUs.

    There are two primary implementations:

    1. MJX-JAX: A JAX re-implementation of MuJoCo.
    2. MJX-Warp: An implementation optimized specifically for NVIDIA GPUs to resolve performance bottlenecks found in MJX-JAX.

    MJX is distributed as the mujoco-mjx package and requires the core mujoco package for model compilation and visualization.

  11. What is the MJCF SdfFileFormat plugin?

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    The MJCF SdfFileFormat plugin is a component for the OpenUSD framework that enables USD-aware applications to treat MuJoCo's native .xml (MJCF) files as first-class USD files. It allows USD to understand the serialization and composition of MJCF data, enabling seamless interoperability between MuJoCo physics assets and the USD ecosystem.

  12. Overview of MuJoCo extension mechanisms

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    MuJoCo provides three primary mechanisms for users to author extensions to the engine:

    1. Engine Plugins: Used to extend the core engine functionality.
    2. Decoders: Used to extend how MuJoCo parses and interprets model files.
    3. Resource Providers: Used to extend how MuJoCo locates and loads external resources (like textures or meshes).