feat(robots): add MIT-mode option to reBot B601-DM follower

Adds a control_mode config field ("pos_vel" default, "mit" optional) for
the reBot B601-DM follower. The arm joints switch between POS_VEL (existing
behavior, firmware-internal PID) and MIT (caller-supplied kp/kd, exposed via
mit_kp / mit_kd config fields, defaulting to 100 / 3). The gripper stays in
FORCE_POS in both modes.

Both scalar and per-joint list values are accepted for mit_kp / mit_kd, same
shape convention as pos_vel_velocity. The bi-manual wrapper threads the new
fields through to each per-arm config.

Default control_mode is "pos_vel" so existing configs are unaffected.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lerobot/robots/bi_rebot_b601_follower/bi_rebot_b601_follower.py

@@ -51,7 +51,10 @@ class BiRebotB601Follower(Robot):
             max_relative_target=config.left_arm_config.max_relative_target,
             cameras=config.left_arm_config.cameras,
             motor_can_ids=config.left_arm_config.motor_can_ids,
+            control_mode=config.left_arm_config.control_mode,
             pos_vel_velocity=config.left_arm_config.pos_vel_velocity,
+            mit_kp=config.left_arm_config.mit_kp,
+            mit_kd=config.left_arm_config.mit_kd,
             gripper_torque_ratio=config.left_arm_config.gripper_torque_ratio,
             joint_limits=config.left_arm_config.joint_limits,
         )
@@ -66,7 +69,10 @@ class BiRebotB601Follower(Robot):
             max_relative_target=config.right_arm_config.max_relative_target,
             cameras=config.right_arm_config.cameras,
             motor_can_ids=config.right_arm_config.motor_can_ids,
+            control_mode=config.right_arm_config.control_mode,
             pos_vel_velocity=config.right_arm_config.pos_vel_velocity,
+            mit_kp=config.right_arm_config.mit_kp,
+            mit_kd=config.right_arm_config.mit_kd,
             gripper_torque_ratio=config.right_arm_config.gripper_torque_ratio,
             joint_limits=config.right_arm_config.joint_limits,
         )

src/lerobot/robots/rebot_b601_follower/config_rebot_b601_follower.py

@@ -65,10 +65,24 @@ class RebotB601FollowerConfig:
         }
     )
 
-    # Target velocity for joints running in POS_VEL mode, in degrees/s. A scalar is
-    # applied to every joint; a list provides one value per joint (in motor order).
+    # Control mode for the arm joints (the gripper always runs in FORCE_POS):
+    #   "pos_vel" - position control with velocity limit (firmware PID gains)
+    #   "mit"     - full impedance control with caller-supplied kp/kd
+    control_mode: str = "pos_vel"
+
+    # Target velocity for joints in POS_VEL mode, or velocity feedforward for joints
+    # in MIT mode, in degrees/s. Scalar applies to every joint; a list gives one
+    # value per joint (in motor order).
     pos_vel_velocity: float | list[float] = field(default_factory=lambda: [150.0] * 7)
 
+    # MIT-mode position stiffness (Nm/rad). Scalar applies to every arm joint; a
+    # list gives one value per joint (in motor order). Ignored when control_mode
+    # is "pos_vel". The gripper entry is unused (gripper stays in FORCE_POS).
+    mit_kp: float | list[float] = 100.0
+
+    # MIT-mode velocity damping (Nm·s/rad). Same shape conventions as ``mit_kp``.
+    mit_kd: float | list[float] = 3.0
+
     # Torque/current ratio for the gripper's FORCE_POS mode, in range [0, 1].
     gripper_torque_ratio: float = 0.1
 

src/lerobot/robots/rebot_b601_follower/rebot_b601_follower.py

@@ -38,7 +38,8 @@ else:
 
 logger = logging.getLogger(__name__)
 
-# Joint controlled in FORCE_POS mode; every other joint runs in POS_VEL mode.
+# Joint always controlled in FORCE_POS mode; every other joint runs in the mode
+# selected by ``RebotB601FollowerConfig.control_mode`` (POS_VEL or MIT).
 GRIPPER_MOTOR = "gripper"
 # Per-joint Damiao motor models for the B601-DM (passed to motorbridge).
 MOTOR_MODELS = {
@@ -168,12 +169,22 @@ class RebotB601Follower(Robot):
         self._save_calibration()
         print(f"Calibration saved to {self.calibration_fpath}")
 
+    def _arm_mode(self):
+        """MotorBridge mode used for the arm joints (gripper always uses FORCE_POS)."""
+        mode = self.config.control_mode
+        if mode == "pos_vel":
+            return MotorBridgeMode.POS_VEL
+        if mode == "mit":
+            return MotorBridgeMode.MIT
+        raise ValueError(
+            f"Unsupported control_mode '{mode}'. Use 'pos_vel' or 'mit'."
+        )
+
     def configure(self) -> None:
         self.bus.enable_all()
+        arm_mode = self._arm_mode()
         for motor_name, motor in self.motors.items():
-            target_mode = (
-                MotorBridgeMode.FORCE_POS if motor_name == GRIPPER_MOTOR else MotorBridgeMode.POS_VEL
-            )
+            target_mode = MotorBridgeMode.FORCE_POS if motor_name == GRIPPER_MOTOR else arm_mode
             for attempt in range(_ENSURE_MODE_RETRIES + 1):
                 try:
                     motor.ensure_mode(target_mode)
@@ -252,6 +263,7 @@ class RebotB601Follower(Robot):
             goal_present_pos = {key: (g, present_pos.get(key, g)) for key, g in goal_pos.items()}
             goal_pos = ensure_safe_goal_position(goal_present_pos, self.config.max_relative_target)
 
+        use_mit = self.config.control_mode == "mit"
         for motor_name, position_deg in goal_pos.items():
             motor = self.motors.get(motor_name)
             if motor is None:
@@ -266,6 +278,10 @@ class RebotB601Follower(Robot):
             vel_rad = math.radians(vel_deg_s)
             if motor_name == GRIPPER_MOTOR:
                 motor.send_force_pos(pos_rad, vel_rad, self.config.gripper_torque_ratio)
+            elif use_mit:
+                kp = self.config.mit_kp[idx] if isinstance(self.config.mit_kp, list) else self.config.mit_kp
+                kd = self.config.mit_kd[idx] if isinstance(self.config.mit_kd, list) else self.config.mit_kd
+                motor.send_mit(pos_rad, vel_rad, kp, kd, 0.0)
             else:
                 motor.send_pos_vel(pos_rad, vel_rad)