Hand Models

This section covers everything related to the DexHand models in MuJoCo, from model conversion to configuration and usage.

Left: Original full mesh-based collision geometries. Right: Simplified collision geometries using primitives.

Contents

• URDF to MJCF Conversion
  • Conversion Process
  • Model Hierarchy
  • Configuration Files
  • Implementation Details
  • Customization
  • Troubleshooting
  • Next Steps
• Collision Models
  • Collision Model Types
  • Configuration
  • Usage
  • Collision Groups
  • Collision Exclusions
  • Implementation
  • Performance Considerations
  • Troubleshooting
  • Next Steps
• Actuators
  • Actuator System
  • Default Configuration
  • Configuration Parameters
  • Implementation
  • Usage
  • Custom Configuration
  • Troubleshooting
  • Next Steps
• Sensors
  • Sensor System Overview
  • Components
  • Implementation
  • Site Parameters
  • Usage
  • Configuration
  • Advanced Usage
  • Troubleshooting
  • Next Steps
• Articulation
  • Overview
  • Basic Concepts
  • Usage
  • Implementation
  • Advanced Features
  • Common Use Cases
  • Troubleshooting
  • Next Steps
• Hand Model Examples
  • Basic Examples
  • Advanced Examples
  • Recording Examples
  • Custom Configurations
  • Next Steps

Overview

The DexHand models in MuJoCo are created through a systematic process that involves:

1. Converting URDF models to MJCF format

2. Optimizing collision geometries

3. Configuring actuator properties

4. Adding sensors and sites

5. Setting up articulation capabilities

Model Structure

Core Components

• Base Link: Provides anchor point for floating base or robot arm attachment

• Finger Links: 5 fingers with multiple joints each

• Palm Links: Structural components of the palm

• Sites: Points of interest for sensors and visualization

• Actuators: Position-controlled joints with configurable parameters

• Sensors: Touch sensors at fingertips

• Collision Geometries: Simplified or full mesh-based

Available Models

• dexhand021_right.xml: Right hand with full collision meshes

• dexhand021_left.xml: Left hand with full collision meshes

• dexhand021_right_simplified.xml: Right hand with optimized collision geometries

• dexhand021_left_simplified.xml: Left hand with optimized collision geometries

• dexhand021_right_floating.xml: Right hand with 6-DoF floating base

• dexhand021_right_jaka_zu7.xml: Right hand mounted on JAKA Zu7 arm

You can also check out Articulation for more details on creating custom models by articulating the hand with your own robot arm.

Joint Configuration

Hand Joint Structure

Each finger has multiple joints:

• Joint 1: Base rotation/spread (1 DoF)

• Joint 2-4: Bending joints (1 DoF each)

Default Joint Ranges

# Bend joints (joints 2-4)
r"[lr]_f_joint[1-5]_[2-4]":
    ctrlrange: "0 1.3"     # 0 to 1.3 radians
    forcerange: "-20 20"   # -20 to 20 N

# Base rotation joints
"r_f_joint1_1":  # Thumb
    ctrlrange: "0 2.2"
"r_f_joint2_1":  # Index
    ctrlrange: "0 0.3"
"r_f_joint3_1":  # Middle
    ctrlrange: "-0.0001 0.0001"
"r_f_joint4_1":  # Ring
    ctrlrange: "0 0.3"
"r_f_joint5_1":  # Pinky
    ctrlrange: "0 0.6"

Next Steps

The following sections provide detailed information about each aspect of the hand models:

• URDF to MJCF Conversion - Converting URDF models to MJCF

• Collision Models - Working with collision geometries

• Actuators - Configuring joint actuators

• Sensors - Setting up touch sensors

• Articulation - Attaching hands to other models

• Hand Model Examples - Example configurations and use cases

Choose a section based on your needs, or follow them in order for a complete understanding of the hand models.

Common Tasks

Converting a URDF Model

python scripts/convert_hand.py --urdf path/to/hand.urdf

Using Simplified Collisions

python scripts/convert_hand.py --urdf hand.urdf \
    --simplified-collision config/collision_geoms/dexhand021_right_simplified.yaml

Attaching to a Robot Arm

python scripts/articulate_hand.py \
    --base robot_arm.xml \
    --hand dexhand021_right.xml \
    --output combined_model.xml \
    --euler 0 90 0