Action Graph for swerve drive robot

[ShauryaJain03]

Hi!
My robot is a 4 wheel swerve drive robot and I want to setup the action graph for it so I can control it using ROS2, how can we configure swerve drive action graph in Isaac Sim?
Thanks.

[rgasoto]

Can you give more details on what specifically you plan on doing? do you want to implement a swerve drive controller in sim, and send a cmd_vel, and let the controller resolve your velocity, or will you send the direct joint action commands for the 4 swerve and 4 drive joints?

[ShauryaJain03]

Hey, thanks for replying. I’d like this to work similar to the Differential Controller OmniGraph setup in Isaac Sim, meaning
I publish geometry_msgs/Twist to /cmd_vel and the robot moves accordingly. Thus, allowing me to teleop the robot and also move it using my control algorithms to test my software stack.
Could you tell me how I can structure the omnigraph and if there is a swerve controller node present within Isaac Sim or will I have to write one myself.

[rgasoto]

Understood - In this case you'll need to implement a controller to drive the wheels correctly - See how the directional drive and Holonomic drive controlers were done. You need to configure it to tell what are the joints that are to be driven, so the controller can make the proper calculation.
The holonomic controller may be a good starting point for you to implement it even - I believe the problem is somewhat analogous, but with a different foundation and way to drive.
https://docs.isaacsim.omniverse.nvidia.com/latest/robot_simulation/mobile_robot_controllers.html#holonomic-controller

[ShauryaJain03]

@rgasoto thanks for the help, I'll reach out again in case I get stuck somewhere. In the meantime, could you please take a look at this issue, I believe a moderator was assigned to this issue, but they might be occupied with some other work. This is turning out to be a blocker for my work and I would appreciate some help with this. Thanks again.

[ShauryaJain03]

@rgasoto is this the correct method for adding custom nodes ?

I wrote .py and .ogn files for swerve drive by copying the structure of the OgnHolonomicController.py and ogn within /isaac-sim/exts/isaacsim.robot.wheeled_robots/isaacsim/robot/wheeled_robots/nodes/

Here are the two files I created - https://github.com/ShauryaJain03/Swerve-Drive-Isaac-Sim

Is this the correct approach, if yes then how do I register it as a node so I can use it to build the omnigraph?

[vick-yu]

Good question — you’re on the right track.

You can indeed define a custom OmniGraph node with a .ogn plus a corresponding Python implementation, and placing them alongside existing controller nodes (like OgnHolonomicController) inside an extension is a valid pattern. The key piece you’re missing is that OmniGraph discovers nodes through extensions, so the files need to live in an enabled extension that’s on Isaac Sim’s extension search path, not just as loose files.

There are two common workflows:

• Reuse an existing extension that already has OmniGraph nodes and drop your .py/.ogn into the same nodes (or ogn) folder, then restart Isaac Sim and make sure that extension is enabled in the Extension Manager.
• Or, create your own extension and have your swerve controller node live there; the recommended way is to use the Isaac Sim VS Code Extension Template Generator, which can scaffold an extension with a ready‑to‑use OmniGraph node that shows up in Action Graph once the extension is enabled.

Once your extension is enabled, your OgnSwerveDriveController node should appear in the Action Graph “Add Node” menu under the extension’s namespace, and you can wire it similarly to the Holonomic Controller example. If it doesn’t show up, double‑check the language field and uiName in the .ogn, the Python class name, and that you don’t have syntax errors in the node implementation.

[ShauryaJain03]

Thanks @vick-yu , I was able to create the extension using the VS Code Template Generator and now I can view the node in the action graph "add node" menu, about the wiring of the action graph, is this the correct way or is there some other method I need to follow?
Also did you happen to take a look at the two files here?

[ShauryaJain03]

Hey @vick-yu @rgasoto , could you guys please take a look at the two files and tell me how I can make an action graph based on it? I have been trying since a couple of days but there seems to be something wrong as it is not working.

[vick-yu]

@ShauryaJain03 — the main reason the action graph “is not working” is a mismatch between your Swerve node’s outputs and what the Articulation Controller expects, not a bug in your .py/.ogn logic.

Your OgnSwerveDriveController node has two outputs:

• driveVelocityCommand (double[], 4) — drive wheel angular velocities (rad/s)
• steeringAngleCommand (double[], 4) — steering angles (rad)

The Articulation Controller node has a single position input and a single velocity input, each meant for all commanded joints. Per the Articulation Controller usage guidelines:

Parameter Validation: Ensure joint commands match the order and number of joint indices or joint names. If neither joint indices nor joint names are specified, the command must match the total number of joints in the robot.

For a 4‑wheel swerve (8 DOFs: 4 steer + 4 drive), that means you must feed:

positionCommand — one array of length 8 (steer angles in the steer-joint slots, in the same order as your robot’s joints)
velocityCommand — one array of length 8 (drive velocities in the drive-joint slots, same order)
You can’t connect driveVelocityCommand (4 values) and steeringAngleCommand (4 values) directly to the Articulation Controller, because it expects one position array and one velocity array, each of length 8 and in joint order (as defined by jointNames / jointIndices on the Articulation Controller).

[vick-yu]

Closing as resolved — the root cause (output array shape mismatch between the custom swerve node and Articulation Controller) was identified above. To summarize: merge your 4-element steeringAngleCommand and driveVelocityCommand into single 8-element positionCommand/velocityCommand arrays matching your robot's joint order. Feel free to reopen or start a new discussion if you hit further issues.