Fix Unitree Go1 and Go2 calf actuator limits

Both configurations applied one set of DC motor limits to all twelve leg
joints, but the Go1 and Go2 calf sits behind an extra knee reduction
(1.50:1 and 1.92:1). The calf was therefore capped at roughly half its
rated torque while its torque-speed curve kept motoring up to a no-load
speed it cannot reach on hardware.

Give the calf its own limits, taken from the joint drives authored in
go1.usd and go2.usd, which already carry the reduction. The hip and thigh
limits are aligned with the same assets so all three come from one source.

Author: AntoineRichard

source/isaaclab_assets/changelog.d/fix-unitree-knee-reduction.minor.rst

@@ -0,0 +1,11 @@
+Fixed
+^^^^^
+
+* Fixed the Unitree Go1 and Go2 leg actuator limits ignoring the knee reduction. Both robots applied
+  the hip and thigh limits to the calf joints, which capped calf torque well below its rated value and
+  let the torque-speed curve keep motoring past its rated speed. The calf joints now use the limits
+  authored in ``go1.usd`` and ``go2.usd`` (Go1: 35.55 N·m, 20.06 rad/s; Go2: 45.43 N·m, 15.70 rad/s),
+  and the hip and thigh limits were aligned with the same assets (23.7 N·m, 30.1 rad/s).
+
+  These robots now produce more calf torque at lower calf speeds, so policies trained on the previous
+  configuration should be retrained rather than reused directly.

source/isaaclab_assets/isaaclab_assets/robots/unitree.py

@@ -39,9 +39,11 @@
     torque_scale=1.0,
     input_order="pos_vel",
     input_idx=[0, 1, 2],
-    actuator_effort_limit=23.7,  # taken from spec sheet
-    actuator_velocity_limit=30.0,  # taken from spec sheet
-    saturation_effort=23.7,  # same as effort limit
+    # the calf sits behind an extra 1.5:1 knee reduction, so its joint-side torque is higher
+    # and its joint-side speed lower than the hip and thigh. Values match ``go1.usd``.
+    actuator_effort_limit={".*_hip_joint": 23.7, ".*_thigh_joint": 23.7, ".*_calf_joint": 35.55},
+    actuator_velocity_limit={".*_hip_joint": 30.1, ".*_thigh_joint": 30.1, ".*_calf_joint": 20.06},
+    saturation_effort={".*_hip_joint": 23.7, ".*_thigh_joint": 23.7, ".*_calf_joint": 35.55},
 )
 """Configuration of Go1 actuators using MLP model.
 
@@ -171,9 +173,11 @@
     actuators={
         "base_legs": DCMotorCfg(
             joint_names_expr=[".*_hip_joint", ".*_thigh_joint", ".*_calf_joint"],
-            actuator_effort_limit=23.5,
-            saturation_effort=23.5,
-            actuator_velocity_limit=30.0,
+            # the calf sits behind an extra 1.92:1 knee reduction, so its joint-side torque is
+            # higher and its joint-side speed lower than the hip and thigh. Values match ``go2.usd``.
+            actuator_effort_limit={".*_hip_joint": 23.7, ".*_thigh_joint": 23.7, ".*_calf_joint": 45.43},
+            saturation_effort={".*_hip_joint": 23.7, ".*_thigh_joint": 23.7, ".*_calf_joint": 45.43},
+            actuator_velocity_limit={".*_hip_joint": 30.1, ".*_thigh_joint": 30.1, ".*_calf_joint": 15.70},
             stiffness=25.0,
             damping=0.5,
             friction=0.0,