[Question] How to set the gravity mode of object?

[jo-choi]

Hi,

When setting up my scene in isaac lab, if I defined an object using RigidObjectCfg and initially set disable_gravity=False via rigid_pros parameter using sim_utils.RigidBodyPropertiesCfg, how can I change it to disable_gravity=True (means zero gravity mode) at a specific point during the simulation?

If it doesn't work, Is there any solution?

Thank you in advance.

[Mayankm96]

Hi @cjoattesollo ,

If you go to the root PhysX view for the rigid body asset class, there is a function named: set_disable_gravities which allows you to set this attribute.

You can probably do something like this (not tested):

current_gravity_status = my_cube.root_physx_view.get_disable_gravities()
current_gravity_status[env_ids] = 0  # need to check if 0 means enable or disable
my_cube.root_physx_view.get_disable_gravities(current_gravity_status, env_ids)

[jo-choi]

Thank you for the quick reply. I will try and get back with the result!

[jo-choi]

It works well with object.root_physx_view.set_disable_gravities(current_gravity_status, env_ids(Tensor)) . Thank you again :)

Checkpoint: 0: disable_gravity=False(with gravity) / 1: disable_gravity=True(without gravity)

[strn18]

Does anyone know why this doesn't work for me?
I'm trying to make an object start without gravity and then enable gravity for it after one second.
Here’s my scene configuration:

@configclass
class MySceneCfg(InteractiveSceneCfg):
    # objects
    object: RigidObjectCfg = RigidObjectCfg(
        prim_path="{ENV_REGEX_NS}/object",
        spawn=sim_utils.UsdFileCfg(
            usd_path=".../objec.usd",
            rigid_props=sim_utils.RigidBodyPropertiesCfg(
                kinematic_enabled=False,
                disable_gravity=True,
                enable_gyroscopic_forces=True,
                solver_position_iteration_count=8,
                solver_velocity_iteration_count=0,
                sleep_threshold=0.005,
                stabilization_threshold=0.0025,
                max_depenetration_velocity=1000.0,
            ),
            mass_props=sim_utils.MassPropertiesCfg(density=400.0),
            visual_material=sim_utils.PreviewSurfaceCfg(diffuse_color=(0.95, 0.8, 0.3)),
        ),
        init_state=RigidObjectCfg.InitialStateCfg(pos=(0.0, 0.0, 0.5), rot=(1.0, 0.0, 0.0, 0.0)),
    )

    # lights
    light = AssetBaseCfg(
        prim_path="/World/light",
        spawn=sim_utils.DistantLightCfg(color=(0.95, 0.95, 0.95), intensity=1000.0),
    )

    dome_light = AssetBaseCfg(
        prim_path="/World/domeLight",
        spawn=sim_utils.DomeLightCfg(color=(0.02, 0.02, 0.02), intensity=1000.0),
    )

As shown, I set disable_gravity=True in the object’s rigid body properties so that it stays fixed at its initial position when the environment starts.

After one second, I run the following function (triggered by one of my EventTerm):

def enable_object_gravity(
    env: ManagerBasedEnv,
    env_ids: torch.Tensor,
    asset_cfg: SceneEntityCfg = SceneEntityCfg("object"),
):
    """Enable gravity for the given asset.
    """
    # extract the used quantities (to enable type-hinting)
    asset: RigidObject = env.scene[asset_cfg.name]

    cur_gravity_status = asset.root_physx_view.get_disable_gravities()
    cur_gravity_status[env_ids] = 0

    asset.root_physx_view.set_disable_gravities(cur_gravity_status, env_ids.to(cur_gravity_status.device))

I confirmed that:

• The function is indeed called one second after the environment starts.
• The value of asset.root_physx_view.get_disable_gravities() changes to 0 after execution.

However, despite these checks, the object does not fall as expected. It stays in its initial position as if gravity were still disabled.