diff --git a/src/lerobot/robots/so100_follower/robot_kinematic_processor.py b/src/lerobot/robots/so100_follower/robot_kinematic_processor.py
index 67e9f9e1e..3874d711c 100644
--- a/src/lerobot/robots/so100_follower/robot_kinematic_processor.py
+++ b/src/lerobot/robots/so100_follower/robot_kinematic_processor.py
@@ -435,22 +435,23 @@ class ForwardKinematicsJointsToEE(ObservationProcessorStep):
     kinematics: RobotKinematics
     motor_names: list[str]
 
-    def observation(self, obs: dict) -> dict:
-        if not all(f"{OBS_STATE}.{n}.pos" in obs for n in self.motor_names):
+    def observation(self, observation: dict) -> dict:
+        print("observation in step", observation)
+        if not all(f"{n}.pos" in observation for n in self.motor_names):
             raise ValueError(f"Missing required joint positions for motors: {self.motor_names}")
 
-        q = np.array([obs[f"{OBS_STATE}.{n}.pos"] for n in self.motor_names], dtype=float)
+        q = np.array([observation[f"{n}.pos"] for n in self.motor_names], dtype=float)
         t = self.kinematics.forward_kinematics(q)
         pos = t[:3, 3]
         tw = Rotation.from_matrix(t[:3, :3]).as_rotvec()
 
-        obs[f"{OBS_STATE}.ee.x"] = float(pos[0])
-        obs[f"{OBS_STATE}.ee.y"] = float(pos[1])
-        obs[f"{OBS_STATE}.ee.z"] = float(pos[2])
-        obs[f"{OBS_STATE}.ee.wx"] = float(tw[0])
-        obs[f"{OBS_STATE}.ee.wy"] = float(tw[1])
-        obs[f"{OBS_STATE}.ee.wz"] = float(tw[2])
-        return obs
+        observation[f"{OBS_STATE}.ee.x"] = float(pos[0])
+        observation[f"{OBS_STATE}.ee.y"] = float(pos[1])
+        observation[f"{OBS_STATE}.ee.z"] = float(pos[2])
+        observation[f"{OBS_STATE}.ee.wx"] = float(tw[0])
+        observation[f"{OBS_STATE}.ee.wy"] = float(tw[1])
+        observation[f"{OBS_STATE}.ee.wz"] = float(tw[2])
+        return observation
 
     def transform_features(
         self, features: dict[PipelineFeatureType, dict[str, PolicyFeature]]