Building a Simple Robot#
In this first lesson, you will learn how to build a simple robot using Isaac Sim. You will navigate the interface, create and configure basic components like the chassis and wheels, and set up physics to simulate realistic movements. By the end of this lesson, you will have a foundational understanding of constructing a robot model that can interact with its environment.
Learning Objectives#
In this lesson, we will:
Navigate the Isaac Sim interface to effectively manage simulations.
Create a visual mesh and enable physics for basic shapes.
Configure hierarchical structures to organize robot components.
Apply revolute joints to enable wheel movement.
Simulate the robot’s movement by adding drive forces.
Building a Simple Robot#
Now that we can confidently navigate the Isaac Sim interface, let’s construct a basic robot model within Isaac Sim. This section will guide you through creating a visual mesh for the robot’s chassis and adding essential components like wheels and joints. You’ll learn how to enable physics to simulate realistic movements and interactions, ensuring your robot can navigate its environment effectively.
By the end of this section, you’ll have a functional robot model ready for further enhancements and control mechanisms in subsequent lessons.
Creating a Visual Mesh#
Start by creating a cube in the scene.
Select Create > Mesh > Cube to create a cube in your scene.
Note
The cube created is a visual mesh, which is what we see in the viewport. However, this cube is not yet defined as a physics object.
Enabling Physics in the Scene#
Press the Play button to simulate physics in the scene.
Observe that nothing happens. This is because the cube is not yet a physics object and has no colliders.
To enable physics in the scene, go to Create > Physics > Physics Scene.
This provides mechanics such as gravity and other needed forces for simulations.
Look at the default properties of the physics scene. See that gravity is set to Earth Gravity, and in Isaac Sim, the up/down axis is in Z.
Refer to the axis indicator in the bottom left of the viewport for orientation.
Adding Physics to the Cube#
Press Play again, and still, nothing happens.
This is because the scene understands that there is physics in the scene, but the cube is still not a physics object.
To fix this, right-click on the cube in the Stage window and select Add > Physics > Rigid Body with Colliders Preset.
The difference between the visual mesh and the collision mesh: The visual mesh is what we see in the viewport, while the collision mesh provides the way that the object interacts with other objects and how other objects react with it.
Open the Show icon, then select Show by Type > Physics > Colliders > Selected.
Now, we can see the green mesh showing us the collision mesh on the cube.
Simulating Physics With a Ground Plane#
Select Play to see what happens.
The cube falls indefinitely because there is no ground plane to stop it.
To prevent the cube from falling indefinitely, we need to add a ground plane. This is an infinitely extended plane that prevents all physics objects from going underneath it.
Add a ground plane through Create > Physics > Ground plane.
Notice that the visual mesh has an end, but the collision mesh continues infinitely.
Expand the GroundFloor xform to find a CollisionMesh and the CollisionPlane.
Move the cube to be above the ground plane. Remember that the default unit in Isaac Sim is meters (m), so raise the cube up to 1 meter.
Final Simulation: Press Play again.
Notice how the cube stops falling when it hits the ground plane. This is the interaction we would expect in a physics simulation.
Additional Notes#
Try changing the gravity direction in the physics scene properties to see how it affects the simulation.
Note
When importing assets into Isaac Sim, different importers will bring in different sets of data. For example, URDF importers can bring in defined physics data, while Isaac Sim importers will only bring in visual data. This is important to keep in mind when working with various assets in Isaac Sim.
SAVE
Go to File > Save to save your work!
Adding the Four Wheels#
Moving on, let’s enhance our Simple Robot by attaching wheels and configuring them for movement. You’ll start by preparing the chassis and understanding the importance of hierarchies in organizing robot components. Next, you’ll create and position the wheels, ensuring they are correctly aligned and attached to the robot’s body. You’ll also add physics properties to the wheels, allowing them to interact with the environment. Finally, you’ll configure revolute joints for rotational movement and apply drive forces to simulate wheel propulsion.
By the end of this section, your robot will be equipped with functional wheels, ready for dynamic movement in future simulations.
Preparing the Chassis#
Ensure the cube is at the world origin (0, 0, 0). This cube will become the main chassis of our robot.
Scale the cube to 2, 1, 0.5. The 2 in the X dimension allows for the front and back wheels.
Understanding the importance of hierarchies in building complex models will help to organize objects, and make transformations and modifications easier.
Creating the Robot Xform and Adding the Chassis#
Create an xform by right-clicking in the Stage panel and selecting Create > Xform. This will serve as the parent for our robot.
Double-click the new xform and rename it to SimpleRobot.
Add the chassis (the cube) to the SimpleRobot xform by dragging it to the SimpleRobot xform in the Stage.
With the SimpleRobot xform selected, find the Transform properties in the Properties tab.
Raise the SimpleRobot up by 1 in the Z-direction.
Observe how the chassis moves up with the xform. This is because the translations are applying to every prim within that SimpleRobot xform, which serves as a container.
Set the height value on the body to 0 to correct this.
Child-Parent Relationships#
As noted in the previous step, the SimpleRobot xform is a container. It creates a child-parent relationship in the stage. Identify the importance of child-parent relationships in hierarchies. This relationship allows for easier management and transformation of objects within the hierarchy.
Creating and Positioning the Wheels#
In the Stage, right-click on SimpleRobot and select Create > Mesh > Cylinder to create a wheel.
Under the transform properties, rotate it 90 degrees in the X dimension and scale it to 0.75, 0.75, 0.25.
Translate the wheel to 0.5, 0.75, 0. This positions the wheel relative to the world axis and the body of the robot.
Rename the cylinder to Front_Left_Wheel by right-clicking it in the Stage panel and selecting Rename.
Duplicate Front_Left_Wheel to create the other three wheels. You can do this by right-clicking and selecting Duplicate, or by pressing Ctrl+D on your keyboard with the prim selected.
Rename each wheel relative to its position (Front_Right_Wheel, Rear_Left_Wheel, Rear_Right_Wheel).
Make sure all wheels are children of the SimpleRobot xform.
Adding Physics to the Wheels and Simulating#
Select all the wheels, right-click, and under Add, select Rigid Body with Collision Preset.
With the wheels selected, see that the collision meshes are now showing.
Press Play and observe how the wheels also fall to the ground due to gravity.
SAVE
Go to File > Save to save your work!
Preparing the Joints#
With our wheels set up, we can focus on enhancing the SimpleRobot by configuring joints that enable wheel movement. This section will guide you through selecting and setting up revolute joints, which allow for rotational movement ideal for wheels. You’ll learn how to configure these joints correctly by adjusting axes and rotations to ensure they align with the wheels’ orientation. Additionally, you’ll create angular drives for the rear wheels to simulate propulsion, setting parameters like velocity and damping for stable control.
By the end of this section, your robot will have fully functional joints, ready to move dynamically in simulations.
Creating Revolute Joints#
Select a wheel. Observe that it is the Y-axis that we want to place the joint on.
Revolute joints allow for rotational movement around a single axis, which is ideal for wheels.
To create a revolute joint, select the parent body Cube first, then, while holding Ctrl select the child prim, (Front_Left_Wheel). Right-click and select Create > Physics > Joint > Revolute joint.
Holding Ctrl will allow you to select both at the same time.
Remember to select the Cube first and then the wheel to allow the joint to set itself up correctly. The order establishes how they move in relation to each other, but it can also be changed later.
Configuring the Revolute Joint#
Note that the default values are incorrect. The default axis is set to X, but we need to change it to Y.
Change the joint axis to Y. Observe that the visualization is now pointing up.
We need to manually set the local rotation 0 of the joint to match the orientation of the prim.
Set the local rotation 0 to 0, 0, 0.
See that the revolute joint now aligns with the orientation of the wheel. Zoom into the joint and notice that the red X arrows are aligned properly, but the blue Z arrows are not.
Set the Local Rotation 1 value to -90, 0, 0 to correct the mismatch.
Deselect and reselect the joint to see the update.
Make sure all the lines are along their correct orientation.
We can ignore the arrow’s pointing direction.
Rename the RevoluteJoint to match the name of the wheel they are connected to, Front_Left_Joint.
Creating the Remaining Joints#
Create the next joints one at a time.
Select the body first, then the next wheel. Create the new joint using the same parameters as the first one.
When finished, move the robot down to the ground plane.
Adding a Drive Force to the Rear Wheels#
We’ll add a drive force to only the rear wheels since the rear wheels are the two that are driving the robot.
Right-click on the joint of the back wheel and select Add > Physics > Angular Drive.
Set the damping for the drive to 10,000.
A large damping value of 10,000 for the rear wheels is chosen to achieve precise velocity control, reduce oscillations, and ensure stability.
Set the target velocity to 50.Because this is an angular drive, the units for velocity are degrees / second.
Repeat for the other rear wheel.
Simulating the Robot#
Press Play to see the robot move forward.
SAVE
Go to File > Save to save your work!
Challenge#
How would you prepare the robot to turn? Try setting a positive value to one wheel and a negative value to the other.
If there are issues, check that the wheels are lower than the body and that the joints are set up correctly. If not, it will drag the robot. Confirm that the joints’ Body 0 and Body 1 values aren’t mixed up. When debugging, double check all the parameters to ensure correct values. One value mistake may cause strange results. Finally, it may be helpful to disable joints one-by-one to narrow down the issue.
Review#
In this lesson, you have successfully built a simple robot in Isaac Sim. You navigated the interface, created a visual mesh for the chassis, and enabled physics to simulate realistic interactions. You also learned to configure hierarchies and apply revolute joints for wheel movement, culminating in a functional robot model.
Learning Objectives#
Navigation of the Isaac Sim interface and becoming familiar with panels and tools.
Created a visual mesh and added physics properties to simulate interactions.
Configured hierarchical structures within your robot model.
Applied revolute joints, allowing for rotational wheel movement.
Simulated the robot’s movement by adding drive forces to the rear wheels.
In the next lesson, you’ll explore preparing and controlling the robot using the keyboard and further enhance its functionality.
Quiz#
Which of the following actions allows you to move the camera forward in the Isaac Sim viewport?
Hold the right mouse button and drag
Use the WASD keys while holding the right mouse button
Use the Q and E keys while holding the left mouse button
Press the Up Key on the keyboard
Answer
B
In Isaac Sim, holding the right mouse button and using the WASD keys allows you to move the camera forward, backward, left, and right in the viewport. This is essential for navigating around your simulation environment.
What must be added to a cube in Isaac Sim to enable it to interact with other objects in a physics simulation?
A visual mesh
A collision mesh
A texture
A light source
Answer
B
A collision mesh defines how an object interacts with other objects in a simulation. While a visual mesh shows what we see in the viewport, it is the collision mesh that allows objects to physically interact within a scene.
Why is it important to use hierarchies when building a robot in Isaac Sim?
It ensures all components are visible in the viewport.
It automatically applies physics to all child objects.
It reduces simulation time.
It helps organize components and simplifies transformations.
Answer
D
Hierarchies are crucial for organizing robot components in Isaac Sim because they allow for easier management of complex models. By grouping related parts under a parent object, transformations like scaling or moving can be applied more efficiently.
What is the primary function of a revolute joint when applied to a robot’s wheels in Isaac Sim?
To allow the wheels to rotate around a fixed point
To move the wheels up and down
To lock the wheels in place
To change the wheel’s shape during simulation
Answer
A
A revolute joint allows for rotational movement around a single axis, which is essential for enabling wheel movement in simulations. This type of joint is commonly used to simulate the rotation of wheels on vehicles or robots.
To simulate forward movement of a robot with rear-wheel drive, what needs to be configured on the rear wheels?
Increase gravity on rear wheels
Change wheel scale to increase friction
Remove collision meshes from front wheels
Add an angular drive with velocity control
Answer
D To simulate wheel propulsion, an angular drive must be added to the rear wheels, which controls their rotational velocity. This enables forward or backward movement by applying forces that simulate real-world driving mechanics.