Physics causing jumps on humanoid robot on flat ground

[MrOCW]

Isaac Sim Version

4.5.0
4.2.0
4.1.0
4.0.0
4.5.0
2023.1.1
2023.1.0-hotfix.1
Other (please specify):

Operating System

Ubuntu 22.04
Ubuntu 20.04
Windows 11
Windows 10
Other (please specify):

GPU Information

• Model: RTX3070Ti
• Driver Version: 560.94

Topic Description

When a G1 humanoid robot is on flat ground, it will jump

Detailed Description

The G1 usd was spawned with stable joint positions. It ends up jumping and sliding on the ground

Steps to Reproduce

1. Set up Physics Scene & Ground Plane
2. Drag a G1.usd onto the scene and play
3. The G1 should start sliding erratically and may also fall over after awhile
4. Change Physics Scene Enable GPU Dynamics to False, Solver Type to PGS
5. Situation improves

Screenshots or Videos

IsaacPhysics.mp4

Related Issues

In Isaac Lab, I am attempting to train the G1 to just balance itself without any velocity commands. The joints are in non optimal positions even though I have a reward function that incentivizes the robot to be in a joint state where it will be balanced without moving. When evaluating the policy, the robot appears to be sliding on the flat ground which causes it to lose balance. When setting Enable GPU Dynamics to False, it will crash due to tensors being on GPU vs CPU

Additional Context

When Enable GPU Dynamics is set to False, my other functionalities will fail, such as collision. Some meshes fail to interact with other prims collisions by phasing through them

[michalin]

Hi @MrOCW, thanks for posting your issue. I tested this on my setup and realized that it is happening due to the coupling between joint drives. If you are using the G1 asset provided by Isaac Sim then this will happen because the Joint Drives are setup by default to very high stiffness with no damping. One way to fix this is to make the stiffness smaller (kp=>1000) and add some damping.

Why is the jumping happening? Simulating the joints with very high stiffness is challenging for a fix step size simulation. If you decrease the simulation step size, then you will be able to get higher fidelity simulation at the cost of slower sim speed (to change sim step go to Windows>Physics Stage Settings>Min Sim frame rate).

Can you try modifying the Joint Drive settings to see if that fixed the issue?

Michael

[michalin]

Hello!

We noticed that this topic hasn’t received any recent responses, so we are closing it for now to help keep the forum organized.

If you’re still experiencing this issue or have additional questions, please feel free to create a new topic with updated details. When doing so, we recommend mentioning or linking to this original topic in your new post—this helps provide context and makes it easier for others to assist you.

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