dora-mujoco

A MuJoCo physics simulation node for the Dora dataflow framework. This node provides real-time physics simulation with support for a wide range of robots from the robot_descriptions package, as well as custom robot models. Designed for modular robotics control architectures.

Features

• Wide Robot Support: Built-in support for 50+ robot models including quadrupeds, humanoids, arms, drones, and more
• Flexible Model Loading: Load robots by name (via robot_descriptions) or direct XML file paths
• Real-time Simulation: Continuous physics simulation with configurable tick rates
• Live Visualization: Optional MuJoCo viewer for real-time 3D visualization
• Generic Control Interface: Accepts control commands for any robot type
• Rich Data Output: Joint positions, velocities, accelerations, and sensor data

Supported Robot Categories

Category	Examples
Quadrupeds	Unitree Go1/Go2/A1, ANYmal B/C, Boston Dynamics Spot
Humanoids	Unitree G1/H1, Apptronik Apollo, TALOS, JVRC-1
Arms	Franka Panda, KUKA iiwa14, Universal Robots UR5e/UR10e
Dual Arms	Aloha 2, Baxter, YuMi
End Effectors	Allegro Hand, Shadow Hand, Robotiq 2F-85
Drones	Crazyflie 2.0, Skydio X2
Educational	Double Pendulum

Getting Started

Quick Start

1. Run a simple simulation:

dora build demo.yml 
# Start with Unitree Go2 quadruped
dora run demo.yml

2. Use different robots:

# In main.py, modify the model name (line ~95)
model_path_or_name = "franka_panda"  # Change this line
# Examples: "go2", "franka_panda", "g1", "spot", etc.

3. Use custom robot models:

# In main.py, use file path instead of model name
model_path_or_name = "/path/to/my_robot/scene.xml"

Usage Examples

TODO

Available Robot Models

The simulator supports all models from the robot_descriptions package. Common names include:

• Quadrupeds: go1, go2, a1, aliengo, anymal_b, anymal_c, spot
• Humanoids: g1, h1, apollo, talos, jvrc, cassie
• Arms: panda, ur5e, ur10e, iiwa14, gen3, sawyer
• Hands: allegro_hand, shadow_hand, leap_hand, robotiq_2f85

See robot_models.json for the complete list.

Architecture

The dora-mujoco node is designed to be robot-agnostic and work with robot-specific controllers:

┌─────────────────┐    
│  Command Node   │    target_pose/cmd_vel
│  (Gamepad, etc) │─────────────┐
└─────────────────┘             │
                                ▼
┌─────────────────┐    control_input   ┌─────────────────┐
│ Robot Controller│───────────────────▶│  dora-mujoco    │
│ (Franka, Husky) │                    │                 │
└─────────────────┘                    │ ┌─────────────┐ │    joint_positions
           ▲                           │ │  Simulator  │ │──────────────────▶
           │        joint_positions    │ │             │ │    joint_velocities  
           └───────────────────────────│ │  ┌────────┐ │ │──────────────────▶
                                       │ │  │Renderer│ │ │    actuator_controls
                                       │ │  └────────┘ │ │──────────────────▶
                                       │ │             │ │    sensor_data
                                       │ └─────────────┘ │──────────────────▶
                                       └─────────────────┘
the control nodes are optional (the robot will still spawn without them)

YAML Specification

Node Configuration

nodes:
  - id: mujoco_sim
    build: pip install -e .
    path: dora-mujoco
    env:
      MODEL_NAME: "go2"  # Robot model name or file path
    inputs:
      TICK: dora/timer/millis/2  # Simulation tick rate (500Hz)
    outputs:
      - joint_positions    # Joint position array
      - joint_velocities   # Joint velocity array  
      - sensor_data       # Sensor readings array

Input Specification

Input	Type	Description
tick	Timer	Triggers simulation steps and data output
control_input	pa.array(float64)	Control commands for actuators

Control Input Format:

• Manipulator Arms: Joint position commands [q1, q2, ..., q7, gripper]
• Mobile Robots: Wheel velocity commands [wheel1, wheel2, wheel3, wheel4]
• Quadrupeds: Joint position commands [hip1, thigh1, calf1, ...]

Output Specification

Output	Type	Description	Metadata
joint_positions	pa.array(float64)	Joint positions (qpos)	timestamp
joint_velocities	pa.array(float64)	Joint velocities (qvel)	timestamp
actuator_controls	pa.array(float64)	Current actuator commands	timestamp
sensor_data	pa.array(float64)	Sensor readings (if available)	timestamp

Configuration Options

Environment Variables

• MODEL_NAME: Robot model name or XML file path (default: "go2")

Custom Robot Models

# Use direct XML file path
env:
  MODEL_NAME: "/path/to/my_robot/scene.xml"

Simulation Parameters

• Physics Timestep: Fixed at MuJoCo default (0.002s = 500Hz)
• Output Rate: Controlled by tick input frequency
• Control Rate: Determined by control_input frequency

Development

Code Quality

# Format code
uv run ruff check . --fix

# Lint code  
uv run ruff check .

# Run tests
uv pip install pytest
uv run pytest .

Adding New Models

To add support for new robot models:

1. Add the model mapping to robot_models.json:

{
  "category_name": {
    "my_robot": "my_robot_mj_description"
  }
}

2. Ensure the model is available in robot_descriptions or provide the XML file path directly.

Creating Robot Controllers

Robot-specific controllers should:

1. Subscribe to joint_positions from the simulation
2. Implement robot-specific control logic (IK, dynamics, etc.)
3. Publish control_input commands to the simulation

Troubleshooting

Common Issues

1. Model not found:

   ERROR: Model file not found for my_robot
   

   • Check if the model name exists in robot_models.json
   • Verify robot_descriptions has the model installed
   • Use absolute file path for custom models

2. Scene variant missing:

   WARNING: Failed to load scene variant
   

   • Normal behavior - falls back to robot-only model
   • Scene variants include ground plane and lighting

3. Control dimension mismatch:

   WARNING: Control input size doesn't match actuators
   

   • Check that control commands match the robot's actuator count
   • Use print(model.nu) to see expected control dimensions

4. Viewer issues:

   • Ensure proper OpenGL/graphics drivers
   • Use headless mode for server environments

Examples

Complete working examples are available in:

• dora/examples/mujoco-sim/
  • Target pose control with Cartesian space control
  • Gamepad control with real-time interaction

License

This project is released under the MIT License. See the LICENSE file for details.

Contributing

Contributions are welcome! Please:

1. Follow the existing code style (ruff formatting)
2. Add tests for new features
3. Update documentation as needed
4. Submit pull requests with clear descriptions

Related Projects

• Dora-rs - The dataflow framework
• MuJoCo - Physics simulation engine
• robot_descriptions - Robot model collection