Step 1: Get a Robot Design

In all seriousness, not everyone is a great designer, and sometimes we'd love to use an existing robot designed by someone else (the Anki Vector for example), you can always find it Design Repositories like GrabCAD

or

Reverse Engineer a 3D Printing Model (Tutorial Coming Soon)

or

Follow the Mechanical Drawings (Good luck finding em), Hope that the text-books are relevant (Yup, that thing in your bag, made of paper) and make your own directly in Autodesk Fusion

Step 2: Create a Project in Fusion

This is just to keep things organized , so its completely optional

Step 3: Upload the Design Files

You dont have to follow this bit tooth n nail

I personally go for a file structure as follows:

.
└── Fusion Project/
    ├── bin/
    │   ├── part1
    │   ├── part2
    │   ├── .
    │   ├── .
    │   ├── .
    │   └── partX
    └── Assembly/
        └── Assembly_Full

Step 4: Make the Full Assembly

This is my favorite part, still feels like Tony Stark

After Creating a new file called Assembly_Full in your Assembly Folder, lets start importing parts from the ground up.

This is a Future-Proofing method that has worked well for me even in clutch situations, where I can iterate quickly by opening the old versions if needed, updating the individual parts in their files, automatically updates the respective component in the assembly, etc.

Assembly_Full is what I call a master design. In this workflow, I copy the master and rename it to a _URDF at the end, as there are a few extra changes to be done to make the URDF. In case, My URDF changes went horrible wrong, somewhere, I can simply delete the _URDF file and create a new copy from the master

Step 4.1: Importing a Referenced Part into the current Design

1. On the Left Pane, navigate to your part of choice
2. Right Click on the part
3. Import into Current Design

As For the Initial Positions, I leave them in Default in most cases, unless the parts overlap and make life not that easier.

Make Sure that the First Link being added needs the Ground to Parent option disabled, as it will be moving to the World Origin anyway

And your Assembly Should Look Something like this:

Step 4.2: Set Part to Origin

By Default the parts you import may not be in World Origin, so lets start by unhiding the Origin.

1. Close the Left Pane if you haven't already (Make use of the whole screen, genius)
2. In the Browser, Check for a folder called Origin
3. Click on the Eye next to Origin to Show the Origin in the Assembly
4. Triple Click anywhere else in the Design to show both the part and the World Origin. It Should Look like something like this:

5. Select the part in the File Browser(Left Pane in the Assembly File) and move the part using the Move Option (Shortcut M) and select the Point-to-Point Mode using the Move Option (Shortcut M) and select the Point-to-Point Mode

1. For the First Point I Chose The Following:
   

And the Second Point as:

And After the Operation, Ends up looking like the following:

Confirm the Operation by Clicking OK and Hide the World Origin by Clicking on the Eye beside the Folder Origin.

Step 4.3 : Capture Position

In Case you are able to see a timeline at the bottom of the window, then you have Design History Enabled. ( Oh which Timeline you say ?...check with the image below:

If So, then On the Top-Right of the Window, Click on the Capture Position to not conflict with any future joints that will be created. The Icon looks something like the following (red highlight)

Step 4.4: Ground the Part

In the Browser, Right Click on the Part, and Click on Ground to Parent

This should pop-up a warning message:

Click on Update Initial Position

Step 4.5: Add More Parts and Create Joints

For the sake of this tutorial, I'll add one more part into the design, so together, thery look like this:

I need a fixed joint, where the top meets the bottom. So Click on Joint (Under Assemble in the Top Panel) or just use the Keyboard Shortcut J

This should open a little widget as follows:

Now here's the tricky part, It needs to follow the logic:

• Component-1 is the new object that has been added. So in this case ,its palm_top and my snapping location is like:

• Component-2 is the old object that is already in the file. In this case, its palm_bottom and the snapping position is like:

🪄 The parts join like magic (I find it magical...deal with it) , but its not over yet.

Although in this case, I'm showing a Rigid Joint , You can head to the Motion tab in the Joint widget and change the type to Revolute, Slider , etc. You can also Preview Motion, although not that important for a Rigid Joint, its instrumental with Revolute and Slider Joints especially to identify the Axis of Rotation and the Axis of Slide respectively. The Motion Tab looks like:

Click OK to confirm the changes.

Step 4.6: Rinse and Repeat

Now Import, the rest of the parts, and join them up like adult lego, or get creative and design your next component around the existing components to the point the assembly looks like a usable robot.

⚠️ Make Sure to Save the file and you can close it

Step 5: Get the fusion2urdf script:

The Repository hosting the URDF Conversion script is here

Open The Zip File, The Contents should look like:

├── URDF_Exporter/
│   ├── utils/
│   │   ├── __init__.py
│   │   └── utils.py
│   ├── package/
│   │   ├── launch/
│   │   │   └── urdf.rviz
│   │   ├── package.xml
│   │   ├── LICENSE
│   │   └── CMakeLists.txt
│   ├── core/
│   │   ├── __init__.py
│   │   ├── Write.py
│   │   ├── Link.py
│   │   └── Joint.py
│   ├── URDF_Exporter.py
│   └── URDF_Exporter.manifest
├── Example
├── README.md
├── LICENSE
└── .gitignore

Copy JUST the URDF_Exporter folder to %APPDATA%\Autodesk\Autodesk Fusion 360\API\Scripts\

The Default Windows Explorer is capable of opening un-encrypted Zip files, but in case you need an archive manager, try WinRAR , 7Zip or Peazip

Verify the Install By Opening Utilities --> Add-Ins –> Scripts and Add-Ins and Check for something Called URDF_Exporter. It should look like something like this:

Step 6: Preparing Model for URDF

Step 6.1: Copy Assembly_Full and Rename Copy to something like Assembly_Full_URDF

• Click on the 9 dot menu (Top Left Corner)
• Navigate to Assembly_Full
• Right-Click
• Copy
• Paste
• Navigate to Assembly_Full copy
• Right-Click
• Rename
• Assembly_Full_URDF

Step 6.2: The Dont's

Step6.2.1 Sub-Assemblies

The repository, doesn't support Sub-Assemblies, Refer to the example below:

Step 6.2.2 Joint Types

The repository on Supports Rigid, Revolute and Slider Joints ONLY, so avoid other joints like Cylinderical, Pin-Slot, Cylinderical, and Ball Joints

Step 6.3: The Do's

Step 6.3.1: File Heirarchy

The Final Assembly (multi-cube icon) should have only Components(cube icon), as seen below:

And Each Component (cube icon) should have only Bodies (silver cylinder icon) and not Meshes (Orange Cloth like icon) as seen below:

Step 6.3.2: Break-Links

If you see a Chain Icon against your Components, that means they are referenced, The script has a few issues while running while linked, to mitigate the issue:

• Select ALL Components with the Chain Icon in the File Browser
• Right Click
• Break-Link

Step 6.3.3: Do Not Capture Design History

Its a Suggestion from the author of the script

• Select the Top Assembly in the File Browser
• Right Click
• Do not Capture Design History

Step 6.3.4: Reduce the number of Joints (Rigid)

As 2 Components that are bonded by a Rigid Body, can be treated as a single body, it makes more sense in the resultant URDF as it becomes easy to control, with only the driving joints in the URDF.

In Step 4.5, I've joined palm_bottom and palm_top using a Rigid Joint, but after the link is broken, You can drag the Body from palm_top to palm_bottom and then delete / remove the Component palm_top, Refer to the flow below (Blue Arrows):

Step 6.3.5: Rename the Grounded Component to base_link

As per the instructions, the component that has been grounded is to be renamed to base_link (Make sure that the Links are Broken)

Step 7: Run Script and Create URDF

Refer to the end of Step 5, but this time run the script by clicking on the Play button.

This will prompt a File Explorer , this the Destination of where you want to export your URDF files

It will take a few seconds, depending on the complexity of the Robot and finally Display a Message Called URDF Exported Successfully

Step 8: Edit the URDF

The Generated URDF has issues with not being compliant for ROS1/ ROS2 Work, primarily due to inconsistencies in the materials. So you need to either comment (Recommended) or remove the parts which mention the material in the URDF.

• Open the Folder where the URDF was Generated in VS Code or any Other editor of Choice
• Open the URDF File
• Search for the following lines:

<material name="silver">
  <color rgba="0.700 0.700 0.700 1.000"/>
</material>

and Replace them lines with:

<!-- <material name="silver">
  <color rgba="0.700 0.700 0.700 1.000"/>
</material> -->

• Search for the following lines:

<material name="silver"/>
    <material/>

and Replace them with:

<!-- <material name="silver"/>
    <material/> -->

Step 9: Add Custom Visuals

The current Repository exports the meshes in the .stl files which do not have the capability of holding data on materials, shaders and textures. But the URDF file format supports other mesh files like .dae (Collada), .wav (Wavefront) and .ply (Stanford) , which all support the above mentioned

⚠️Support for Collada is currently being deprecated from accessible Softwares like Blender since version 4.5 and above

• Download and Install Blender ( Any Version Works) and Open It

Assuming that the Default Settings are being Used

Step 9.1 Texture Painting

• Clear the Current Stage by selecting all the Primatives in the right browser and Delete (Keyboard Shortcut X)
• Import an stl from the /meshes folder in the generated URDF folder by

File --> Import --> STL(.stl) --> Navigate to .stl

By Default, The STL file is imported with the Y being the Forward Axis and Z being the Up Axis

• Switch from Object Mode to Edit Mode ( keyboard Shortcut Tab) and Face Select Mode

• In the Properties Menu , Click on Materials Options, Click + to add a new Material Slot and then on New to create a New Material, Refer to the image below.

• Rename the Newly Created Material (Recommended), Change the Base Color to any HSV value, other properties like Mettalic, Roughness, Sheen , etc. can also be edited. Refer to the Image Below:

• Change the Viewport to Shading Mode, Refer to the Image Below

• While You are in Edit Mode, use Circle Select (Select --> Circle Select or Keyboard Shortcut C) to select the faces that you want to change appearance of.

The Radius of the Circle Select cursor can be varied using the Scroll Wheel on the Mouse

• Then in the Properties Menu, select the Newly Created Material and click on Assign., Refer to the Image Below:

• Create new Material Slots and Materials as per requirement to Change the appearance of the Mesh

Step 9.2: Export Textured Mesh

• Make Sure that there is only one mesh being Textured at a time
• Switch back from Edit Mode to Object Mode
• Select the Mesh
• In the Top Taskbar. File --> Export --> Standord PLY (.ply)
• In the right Taskbar (Operator Presets)....In General make sure that the Forward Axis is at Y and Up Axis is at Z.
• In Geometry, I have enabled UV Coordinates, Vertex Attributes, Apply Modifiers.

• If the base_link.stl was imported then make sure that it is exported as base_link.ply in the same location(/meshes).

Step 9.3: Repeat 9.1 and 9.2 for all other meshes of the Robot

Dont Worry! The process takes even lesser time with practice... keep at it (Or help me make a new tool...Thanx in Advance)

Step 10: Modify the URDF to use .ply instead .stl

Since the .ply files are saved in the same location as the .stl files, this final modification is pretty straightforward and simple.

• Open the URDF file in VS Code.
• Search (Ctrl + F) for .stl
• Replace (Ctrl + H) with .ply
• Save (Ctrl + S)

Validation

Now to Visualize the URDF, we use the urdf-viz project.

Installation

Linux:

sudo apt-get install cargo cmake xorg-dev libglu1-mesa-dev -y
cargo install urdf-viz --features assimp

Windows:

Download the windows the Binary from the Releases page of the urdf-viz Project and extract .exe file in the same location as the .urdf file.

Usage:

Linux:

• Open the Terminal

cd path/to/urdf/folder
urdf-viz robot.urdf 

Windows:

• Open Terminal (CMD)

cd path/to/urdf/folder
urdf-viz.exe robot.urdf

OR

• Open Terminal (Powershell)

cd path/to/urdf/folder
.\urdf-viz.exe robot.urdf

Output: