[Question] How to find body with fixed frame?

[jo-choi]

Hi all,

Previously, I was able to find the body named "link_tcp" using self._robot.find_bodies("link_tcp")[0][0] with the older URDF exporter. However, in the current setup (latest version), "link_tcp" is defined as a <fixed_frame> with a parent link "link_base", and it does not appear in the list of available bodies.
In this case, what is the correct way to access or reference "link_tcp"?

<fixed_frame name="link_tcp">
 <parent link="link_base"/> 
 <origin rpy="3.141592653589793 0 0" xyz="0 0 0.22"/>
</fixed_frame> ``` 
Thank you advance.

[jo-choi]

Solved.

For those using DirectRLEnv, here's how I set up the tcp frame:

class EnvCfg(DirectRLEnvCfg):
    robot: ArticulationCfg = DG_CFG.replace(   # type: ignore
        prim_path="/World/envs/env_.*/Robot",
    )

    tcp_frame = FrameTransformerCfg(
        prim_path="/World/envs/env_.*/Robot/link_0",
        debug_vis=False,
        target_frames=[
            FrameTransformerCfg.FrameCfg(
                prim_path="/World/envs/env_.*/Robot/link_dg_base",
                name="link_tcp",
                offset=OffsetCfg(
                    pos=(0.0, 0.0, 0.22),
                    rot=(1, 0, 0, 0),
                ),
            ),
        ],
    )

def _setup_scene(self):
   self._tcp_frame = FrameTransformer(self.cfg.tcp_frame)
   self.scene.sensors["tcp_frame"] = self._tcp_frame
   
# In the training loop:
   tcp_frame_data = self._tcp_frame.data

Hope this helps someone running into the same issue!