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Prepare Robot Model

Using Provided Robot Models

Isaac Sim provides various robot models from popular manufacturers like Universal Robots, Unitree, Franka Robotics etc. by default.

You can access these models by clicking Window -> Browsers -> Isaac Sim Assets.

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There should be a new tab appeared next to the Content tab. You may have to wait for a while for Isaac Sim to load all the assets. There are plenty of robot models here. But if you need your own robot to be implemented, please follow below general setup guide.

Building Robot model

Prerequisites

You can make any robot with all the shapes and sizes you'd like, but there are some rules that need to be addressed.

  • The name of your robot prim must match the name from StellarX.
  • Robot must contain only one articulation root.
  • All the links in the robot must be rigid-bodies. Collision or weight settings is not mandatory, but is recommanded for accurate physics simulation.
  • Closed-loop articulation is not supported. You can exclude some joints from articulation, but this may result in inaccurate simulation result.
  • ( Add more if needed )

Most of the time, you'll be using urdf format. If you wish to use urdf, please refer to this guide. In this tutorial, we'll be rigging the robot ourselves. Before starting, please download the result robot model from 3D Model Creation guide.

Making Robot Model

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  • Open up new file. From main screen, Click File -> Import.
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  • Go to downloaded file's directory. Select the file and enable Use Meter as World Unit. Click box next to Up-axis and select Z-up and import. The result should look like bottom picture.
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  • If you take a look at the file's directory, you'll see a new .usd format file with the same name. Click File -> Open and open the .usd file. You'll be then able to see the full robot model.
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  • Open up all the joint prims and you'll see the full stage tree. Right-click on the empty part of the stage and click Create -> Scope. This will create scope for organizing the stage. Create two scopes and name them links and joints.
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  • Drag all the links to links scope and delete joint prims.
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  • Select all the links and right-click. Click Add -> Physics -> Rigid Body to make them rigid-bodies. You can verify it by scrolling down on the property tab.
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  • Next, open the link prim and select mesh prim. Right-click and click Add -> Physics -> Collider. This will add collider to mesh and you can also verify it by scrolling down. Default collider type is trimesh, but since the parent prim is rigid-body, it is automatically set to Convex Hull. Repeat this for all the other link meshes.
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  • Now, we need to add joints. First, select link0 and right-click. Click Create -> Physics -> Joint -> Fixed Joint. This will create FixedJoint under link0. This joint is like an anchor that fixes base link of the robot to the world. You can see this by looking at the Body settings of FixedJoint. Empty Body 0 means it is fixed to world. You can explicitly set this To /World prim.
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  • Next, we will add revolute joint. Select link0 and then ctrl-click link1. Order matters in this part. Selecting link1 then link0 will result in link0 trying to revolute relative to link1 and not vice versa. Right-click on link1 and click Create -> Physics -> Joint -> Revolute Joint. This will create revolute joint under link1.
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  • Rename joint to J1 for consistency. Right-click on J1 and select Add -> Physics -> Angular Drive. We can only control joints with drive property, and joints without them can only move passively.
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  • Repeat the same process for the other joints. And move them to joints scope.
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  • Select all the active joints and scroll down to Drive property. Set Stiffness and Damping to 100000.0 and 10000.0, resplectively. This is only to set the joints fixed when not using Stellar X. You can choose arbitrary values, only if Stiffness is higher than Damping.
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  • Select J1 and scroll down to Revolute Joint section. Click Axis and selelct Z. Repeat same process for J4 and J6.
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  • Finally, select FixedJoint and right-click. Select Add -> Physics -> Articulation Root. Articulation Root is what defines robot in Isaac Sim. For more information, check out this documentation.
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And that's it! You just made your own robot model. Save and open up new file. Click Create -> Environments -> Flat Grid. Drag the robot model file to Stage on the right, and you'll see the robot in the world!

(Insert example gif here)

Change the robot's name to your StellarX's robot name and click Play button on the left side. Jog the robot via StellarX and you'll see the robot is moving accordingly. You can also write your own python script to move the robot at your need.

You can download final robot model below.

Conclusion

In this tutorial, we set up robot eligible for Isaac Sim environment. Isaac Sim is a powerful tool for robot simulation with numerous features. Check out official Isaac Sim Documentation for more information. If you have questions regarding Isaac Sim, please check out Isaac Sim Forum.