[Bug Report] The `set_physical_attr` function in Articulation fails to properly set the mass.

[wuxinxin27]

Describe the bug

The set_physical_attr function in Articulation fails to properly set the mass.

Steps to reproduce

I loaded a single-joint, two-link articulated pipette body. Although I set the mass parameter to 0.1 in gym_config.json, printing the actual mass of the link loaded into the environment reveals it remains at the default value of 1.0.

  "pipette_tip": {
    "get_mass": 1.0,
    "get_static_friction": 1.2000000476837158,
    "get_dynamic_friction": 1.0,
    "get_restitution": 0.0010000000474974513,
    "get_linear_damping": 0.699999988079071,
    "get_angular_damping": 0.699999988079071,
    "get_max_depenetration_velocity": 2.0
  },
  "pipette_button": {
    "get_mass": 1.0,
    "get_static_friction": 1.2000000476837158,
    "get_dynamic_friction": 1.0,
    "get_restitution": 0.0010000000474974513,
    "get_linear_damping": 0.699999988079071,
    "get_angular_damping": 0.699999988079071,
    "get_max_depenetration_velocity": 2.0
  },

System Info

• Commit: main branch
• OS: Ubuntu 22.04
• GPU: RTX 5060Ti
• CUDA: 12.8
• GPU Driver: 580.142

Additional context

By individually specifying the mass for each link within set_dexsim_articulation_cfg, and then attempting to load and print the mass again, the system returned to normal operation.
Add any other context about the problem here.

      for name in link_names:
          physical_body = art.get_physical_body(name)

          if hasattr(physical_body, "set_mass") and cfg.attrs.mass is not None:
              if cfg.attrs.mass > 0:
                  physical_body.set_mass(cfg.attrs.mass)

The printed result is as follows:

  "pipette_tip": {
    "get_mass": 0.009999999776482582,
    "get_static_friction": 1.2000000476837158,
    "get_dynamic_friction": 1.0,
    "get_restitution": 0.0010000000474974513,
    "get_linear_damping": 0.699999988079071,
    "get_angular_damping": 0.699999988079071,
    "get_max_depenetration_velocity": 2.0
  },
  "pipette_button": {
    "get_mass": 0.009999999776482582,
    "get_static_friction": 1.2000000476837158,
    "get_dynamic_friction": 1.0,
    "get_restitution": 0.0010000000474974513,
    "get_linear_damping": 0.699999988079071,
    "get_angular_damping": 0.699999988079071,
    "get_max_depenetration_velocity": 2.0
  },

Checklist

• I have checked that there is no similar issue in the repo (required)

[yuecideng]

Hi @wuxinxin27 , thanks for reporting this issue.

The current design for articulation is that, we do not read the mass attribute from the cfg, instead we read it from asset file (URDF/USD).
I add a new feature that supporting setting the mass via event functor for articulation: #219

You can define a functor in gym_config like:

        "events": {
            "randomize_articulation_mass": {
                "func": "randomize_articulation_mass",
                "mode": "reset",
                "params": {
                    "entity_cfg": {
                        "uid": "drawer"
                    },
                    "link_names": ["outer_box"],
                    "mass_range": [0.1, 0.1],
                }
            },
          ....

For setting mass for specific link.

        "events": {
            "randomize_articulation_mass": {
                "func": "randomize_articulation_mass",
                "mode": "reset",
                "params": {
                    "entity_cfg": {
                        "uid": "drawer"
                    },
                    "mass_range": {
                        "outer_box": [0.1, 0.1],
                        "inner_box": [0.15, 0.15]
                    },
                }
            },
          ....

Feel free to give feadback if this feature can help you.