URDF

Introduction

URDF is a very standard format that can be exported by onshape-to-robot. Below are the specific configuration entries that can be specified when using this format.

When using this exporter, frames will be added as a dummy links attached to their body using a fixed joint

config.json entries (URDF)

Here is an example of complete config.json file, with details below:

{
    "url": "document-url",
    "output_format": "urdf",
    // ...
    // General import options (see config.json documentation)
    // ...

    // Package name (for ROS) (default: "")
    "package_name": "my_robot",
    // Additional XML file to be included in the URDF (default: "")
    "additional_xml": "my_custom_file.xml",
    // Exclude inertial data for fixed bodies (default: false)
    "set_zero_mass_to_fixed": true,

    // Override joint properties (default: {})
    "joint_properties": {
        // Default properties for all joints
        "*": {
            "max_effort": 10.0,
            "max_velocity": 6.0,
            "friction": 0.5
        },
        // Set the properties for a specific joint
        "joint_name": {
            "max_effort": 20.0,
            "max_velocity": 10.0,
            "friction": 0.1,
            "limits": [0.5, 1.2]
        },
        "wheel": {
            "type": "continuous"
        }
    },

    // Override geometry properties (default: {})
    "geom_properties": {
        // Set properties for specific links using pattern matching
        "tibia": {
            "collision": {
                "mu1": "1.2",
                "mu2": "0.8"
            }
        },
        // Wildcard patterns are supported
        "leg_*": {
            "visual": {
                "material": "leg_material"
            }
        }
    },
}

joint_properties (default: {})

Allow to specify the properties of the joints produced in the URDF output. The key should be joint names. The special default key will set default values for each joints.

Possible values are:

• max_effort: The maximum effort that can be applied to the joint (added in the <joint effort=...> tag)

• max_velocity: The maximum velocity of the joint (added in the <joint velocity=...> tag)

• friction: The friction of the joint (added in the <joint_properties friction=...> tag)

• type: Sets the joint type (changing the <joint type="..."> tag)

• limits: Override the joint limits, should be a list of two values (min, max)

geom_properties (default: {})

Allow to specify the properties of the geometries (collision and visual) produced in the URDF output. The key should be part names with support for wildcard pattern matching.

Properties can be specified separately for visual and collision geometries, or applied to both if not nested.

Wildcard patterns (*, ?, [seq]) are supported for matching part names. When multiple patterns match, properties are merged in order with later matches overriding earlier ones.

All properties are added as nested XML elements within the <visual> or <collision> tags. Common URDF geometry properties include:

• mu1, mu2: Friction coefficients for collision geometries

• kp, kd: Contact stiffness and damping parameters

• material: Material reference for visual geometries

package_name (default: “”)

If you are exporting a URDF for ROS, you can specify the package name here. This will be used in the <robot> tag.

additional_xml (default: “”)

If you want to include additional XML in the URDF, you can specify the path to the file here. This file will be included in the produced URDF file.

Note

Alternatively, additional_xml can be a list of files

set_zero_mass_to_fixed (default: false)

This option sets the mass to 0 for bodies that are fixed to the world.

Note

In PyBullet, such bodies are indeed recognized as fixed