lerobot / unitree-g1-mujoco

Standalone MuJoCo Simulator for Unitree G1

This is a standalone MuJoCo physics simulator for the Unitree G1 robot, extracted from the GR00T-WholeBodyControl repository.

Features

• Physics Simulation : Runs G1 robot in MuJoCo at 500Hz (2ms timestep)
• DDS Communication : Uses Unitree SDK2 DDS for robot communication
• Compatible : Works with existing unitree_g1.py control code via DDS
• Visualization : Real-time 3D visualization of robot motion

Directory Structure

mujoco_sim_g1/
├── requirements.txt          # Python dependencies
├── run_sim.py               # Main launcher script
├── config.yaml              # Simulation configuration
├── sim/                     # Simulation modules
│   ├── base_sim.py
│   ├── simulator_factory.py
│   ├── unitree_sdk2py_bridge.py
│   └── ...
└── assets/                  # Robot models
    ├── g1_29dof_with_hand.xml
    └── meshes/*.STL

Installation

1. Create Virtual Environment (Recommended)

cd mujoco_sim_g1
python3 -m venv venv
source venv/bin/activate  # On Windows: venv\Scripts\activate

2. Install Dependencies

pip install -r requirements.txt

Note : If you encounter issues with rclpy , you can comment out the ROS2 imports in sim/base_sim.py (lines 11, 609-617) if you don't need camera publishing.

Usage

Basic Usage

# Activate environment
source venv/bin/activate

# Run the simulator
python run_sim.py

The simulator will:

1. Load the G1 robot model
2. Initialize DDS communication on domain 0
3. Open a MuJoCo visualization window
4. Start listening for motor commands via DDS

Running with Your Robot Control Code

Once the simulator is running, you can control it from another terminal:

# In another terminal
cd /home/yope/Documents/lerobot
conda activate unitree_lerobot

# Run your existing control code
python test_locomotion_minimal.py

Your unitree_g1.py code will automatically connect to the simulator via DDS!

Configuration

Edit config.yaml to customize:

• SIMULATE_DT : Simulation timestep (default: 0.002s = 500Hz)
• DOMAIN_ID : DDS domain ID (default: 0)
• ENABLE_ONSCREEN : Show visualization (default: true)
• USE_JOYSTICK : Enable gamepad control (default: false)
• ROBOT_SCENE : Path to MuJoCo XML scene

PD Gains

The simulator uses the following PD gains (matching NVIDIA GR00T):

Legs (indices 0-11):

• Hip joints: KP=150, KD=2
• Knee joints: KP=300, KD=4
• Ankle joints: KP=40, KD=2

Waist (indices 12-14):

• All waist joints: KP=250, KD=5

Arms (indices 15-28):

• Shoulders: KP=100, KD=2-5
• Elbows/Wrists: KP=20-40, KD=1-2

Troubleshooting

ImportError: cannot import name 'ChannelFactoryInitialize'

pip install --upgrade unitree-sdk2py

ROS2/rclpy errors

If you don't need camera publishing, edit sim/base_sim.py :

• Comment out line 11: import rclpy
• Comment out lines 609-617 (ROS2 initialization)

Meshes not found

Make sure mesh paths in assets/g1_29dof_with_hand.xml are relative:

<mesh file="meshes/pelvis.STL"/>  <!-- Not absolute path -->

Robot falls immediately

Check that:

1. PD gains match NVIDIA's values (see config.yaml)
2. Velocity command scaling is correct (ang_vel_scale=0.25, cmd_scale=[2.0, 2.0, 0.25])
3. Observations for missing joints are zeroed out (indices 12, 14, 20, 21, 27, 28)

Technical Details

Communication

The simulator publishes:

• rt/lowstate : Robot state (joint positions, velocities, IMU, etc.)
• rt/wirelesscontroller : Wireless remote controller state (if joystick enabled)

The simulator subscribes to:

• rt/lowcmd : Motor commands (position, velocity, torque, KP, KD)

Coordinate Frames

• World frame : Z-up
• Joint ordering : 29 DOF (12 legs + 3 waist + 14 arms)
• IMU : Quaternion in [w, x, y, z] format

Performance

• Simulation runs at ~500Hz (2ms timestep)
• Viewer updates at ~50Hz (20ms)
• Typical CPU usage: 20-40% on single core

Files from GR00T-WholeBodyControl

This standalone simulator was extracted from:

• gr00t_wbc/control/envs/g1/sim/ (simulation modules)
• gr00t_wbc/control/robot_model/model_data/g1/ (robot model files)
• gr00t_wbc/control/main/teleop/configs/g1_29dof_gear_wbc.yaml (configuration)

License

Follows the license of the original GR00T-WholeBodyControl repository.