[Question] how to deal with a robot Including a spring-damper structure in Isaac Sim

[E1chooo]

I have a question related to IsaacSim: how can I add a robot equipped with a spring-damper structure, and what proper approach should I take to simulate this kind of spring-damper system? Please note that this spring-damper is not the stiffness and damping coefficients applied in joint calculations.

I would greatly appreciate any guidance, practical examples or relevant suggestions you could offer to help me solve this problem.

Thank you so much for your time and assistance!

[RandomOakForest]

Thank you for posting this. I'll move this to our Discussions section. Here is a summary to consider that is still under review, but may be of help.

You model a spring-damper in Isaac Sim either as:

1. a joint drive–based virtual spring, or
2. a geometric “mechanism” built from bodies and joints that approximate a physical spring.

Because you explicitly do not want “the stiffness and damping coefficients applied in joint calculations” as your spring, the recommended approach is to construct a dedicated spring-damper mechanism with its own joints, and only use joint drive gains as low-level stabilizers, not as the conceptual spring itself.¹²

What “spring-damper” options exist in Isaac Sim?

Isaac Sim’s PhysX backend exposes spring-damper behavior in three main ways:³¹

• Joint drives (articulations and rigid body joints)
  • Use stiffness/damping on the drive to implement a virtual spring around a target pose or target velocity.⁴⁵⁶
  • This is the standard robotics way (PD control) and is documented in the joint tuning tutorial.⁵⁶
• Soft joint limits and limit springs (non-articulation joints only)
  • Certain PhysX joints (e.g., PxRevoluteJoint) support a limit with a spring and damping that acts when the joint hits the limit.⁷⁸³
  • In Isaac Sim articulations, soft joint limits are currently not supported; limits are hard constraints.⁸
• Compliant contact via material properties
  • Rigid contacts can be made compliant through spring-damper parameters in the material’s advanced contact model, effectively giving “springy” contact behavior between bodies.¹

Since your spring-damper is not the same as the robot joint controller stiffness/damping, you typically:

• Model the robot as one articulation.
• Model the spring-damper structure as an additional mechanism (rigid bodies + joints) that connects robot links or connects robot to environment, with its own geometry and parameters.²¹

Recommended modeling approach for a physical spring-damper

A practical way to add a physical spring-damper between two links (or robot–world) is:

• Use a prismatic or spherical joint chain to represent the compliant element
  • For 1D translational compliance (e.g., linear spring along one axis), create a prismatic joint between two rigid bodies aligned with the spring axis.²
  • For bending/flexible rods, approximate the spring as a chain of capsule segments connected by spherical joints.⁹⁷
• Attach the spring mechanism to the robot
  • Connect one end body of the chain to a link in the robot articulation via a fixed joint or rigid attachment.
  • Connect the other end to another link or to the environment, again using fixed or rigid attachment.¹
• Use drive-based spring behavior only inside the spring mechanism, separate from the robot’s main control logic:
  • On each prismatic or spherical joint of the spring mechanism, set up a drive whose stiffness/damping describe the physical spring constant and damping of that element, rather than the robot’s control gains.⁶⁴⁵
  • The robot’s own actuated joints can then remain torque/position controlled with their own gains, independent of the spring mechanism.

Even though this still uses drive stiffness/damping at the physics level, conceptually you are implementing a distinct “component” whose dynamics are those of a mechanical spring, not the robot servo controller.

For linear springs where you also want visible compression/extension, a commonly used pattern in Isaac Sim is:²

• Drive the physics with a prismatic joint representing compression.
• Render a separate mesh (for the helix or spring graphic) whose scale along the joint axis tracks the prismatic joint displacement, giving you both physical forces and visible deformation.

Implementation details and recommended settings

To add such a spring-damper structure and connect it to your robot in Isaac Sim 6.0 and later:¹⁰⁶¹

• Base physics configuration
  • Ensure your scene uses PhysX with articulations enabled (default in Isaac Sim 4.x–6.x).¹
  • For compliant contact-based “springiness” (e.g., rubber bumpers), configure the rigid material contact model to use spring-damper parameters in the advanced tab.¹
• Spring mechanism construction
  • Create rigid bodies (e.g., capsules or boxes) that form the spring.
  • Add joints between these bodies:
    • Prismatic for axial compression.
    • Spherical for chain-like flexible springs/rods.⁷⁹
  • Place and orient the joints so the drive axis is aligned with the physical direction of elasticity.
• Drive configuration to mimic a physical spring-damper
  • Use the joint tuning methodology in the Isaac Sim joint drive tutorial.⁵⁶
  • Set:
    • A position target equal to the undeformed length / neutral orientation.
    • Stiffness equal to your desired spring constant (scaled as needed by units and masses).⁴⁵
    • Damping about an order of magnitude lower than stiffness as a starting point, then tune for critical or underdamped behavior as needed.⁶⁴⁵
  • Limit the maximum joint force/torque in the drive if you want the spring to saturate.¹¹
• Closed-loop integration with robot
  • If the spring structure closes a kinematic loop on the robot (e.g., parallel linkages or passive elements between links), follow the closed-loop rigging tutorial: break one link, add an extra articulation root or mimic joint, then reconnect using joint drives or constraints.¹⁰
  • This helps keep the articulation solvable while still giving you the structural behavior you want.

Relevant Isaac Sim and PhysX documentation / tutorials

These NVIDIA documentation pages and tutorials give concrete guidance and examples for the components you will use:

• Isaac Sim physics fundamentals (contact and compliance)
  • Physics overview and compliant contact configuration:
    • https://docs.isaacsim.omniverse.nvidia.com/4.2.0/simulation_fundamentals.html[^1]
• Joint drive tuning (for the spring-damper behavior inside your mechanism)
  • Isaac Sim Joint Drive Tuning tutorial (latest 6.0):
    • https://docs.isaacsim.omniverse.nvidia.com/6.0.0/robot_setup_tutorials/joint_tuning.html[^6]
  • Isaac Sim 4.5 joint tuning guide (conceptual discussion of stiffness/damping as spring-damper):
    • https://docs.isaacsim.omniverse.nvidia.com/4.5.0/robot_setup/joint_tuning.html[^5]
• Closed-loop structures (for integrating spring mechanisms into robots)
  • Rigging closed-loop structures and using drives/mimic joints:
    • https://docs.isaacsim.omniverse.nvidia.com/6.0.0/robot_setup_tutorials/rig_closed_loop_structures.html[^10]
• PhysX joint and spring APIs (underlying model)
  • PhysX Joints documentation (limit springs, damping, and drives):
    • https://nvidia-omniverse.github.io/PhysX/physx/5.1.0/docs/Joints.html[^3]
  • Physx Joint Schema in Omniverse (Drive and performance envelope APIs used under the hood):
    • https://docs.omniverse.nvidia.com/kit/docs/omni_physics/latest/dev_guide/joints/physx_joint_schema.html[^11]
• Developer forum threads with recommended patterns
  • “How to simulate the spring in Isaac Sim?” (prismatic joint + visual scaling recommendation):
    • https://forums.developer.nvidia.com/t/how-to-simulate-the-spring-in-isaac-sim/238123[^2]
  • “How to simulate a spring” (joint and limit approaches, plus discussion of PhysX behavior):
    • https://forums.developer.nvidia.com/t/how-to-simulate-a-spring/201491[^12]
  • “Does Isaac Sim support soft joint limits?” (clarifying when soft limit springs are available):
    • https://forums.developer.nvidia.com/t/does-isaacsim-support-soft-joint-limits/311045[^8]

You may consider posting more specific follow up questions in the Isaac Sim GitHub discussions forum here.

Footnotes

1. https://docs.isaacsim.omniverse.nvidia.com/4.2.0/simulation_fundamentals.html ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

2. https://forums.developer.nvidia.com/t/how-to-simulate-the-spring-in-isaac-sim/238123 ↩ ↩² ↩³ ↩⁴

3. https://nvidia-omniverse.github.io/PhysX/physx/5.1.0/docs/Joints.html ↩ ↩²

4. https://docs.omniverse.nvidia.com/kit/docs/omni_physics/107.3/dev_guide/guides/gripper_tuning_example.html ↩ ↩² ↩³ ↩⁴

5. https://docs.isaacsim.omniverse.nvidia.com/4.5.0/robot_setup/joint_tuning.html ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

6. https://docs.isaacsim.omniverse.nvidia.com/6.0.0/robot_setup_tutorials/joint_tuning.html ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

7. https://forums.developer.nvidia.com/t/isaac-sim-4-5-physx-sphericaljoint-soft-limit-springcompliance-damping-not-producing-expected-elastic-return/333914 ↩ ↩² ↩³

8. https://forums.developer.nvidia.com/t/does-isaacsim-support-soft-joint-limits/311045 ↩ ↩²

9. https://forums.developer.nvidia.com/t/spherical-joint-moves-like-spring/335011 ↩ ↩²

10. https://docs.isaacsim.omniverse.nvidia.com/6.0.0/robot_setup_tutorials/rig_closed_loop_structures.html ↩ ↩²

11. https://docs.omniverse.nvidia.com/kit/docs/omni_physics/latest/dev_guide/joints/physx_joint_schema.html ↩