Checkpoint 7

herding/world/diffdrive.py

@@ -1,11 +1,8 @@
-"""Differential-drive kinematics matching the Webots robot specs.
+"""Differential-drive kinematics, shared by the env and Webots controllers.
 
-The Webots controllers and the training env both use these helpers so the
-sim and the real (Webots) physics agree to first order. They do not model
-slip, wheel acceleration limits, or contact forces — Webots does that for
-us at inference time. The training env has to be close enough that a
-policy trained against this kinematic model still works when handed off
-to ODE physics.
+First-order rigid-body model — no slip, wheel-accel limits, or contact
+forces. Webots' ODE physics handles those at inference; the env stays
+close enough to first order that a policy trained here transfers.
 """
 
 import math
@@ -34,10 +31,9 @@ def kinematics_step(x, y, h, w_left, w_right, wheel_radius, wheel_base, dt):
 
 def velocity_to_wheels(vx, vy, h, max_linear, wheel_radius, max_wheel_omega,
                        k_turn=4.0):
-    """Convert a desired (vx, vy) intent in [-1, 1]^2 to wheel speeds.
+    """Convert a desired (vx, vy) intent in [-1, 1]² to wheel speeds.
 
-    Mirrors ``drive_action`` in controllers/shepherd_dog/shepherd_dog.py:
-    forward speed scales by ``cos(err)`` (clamped to ±90°), and a P
+    Forward speed scales by ``cos(err)`` (clamped to ±90°); a P
     controller on heading error contributes the wheel-rate differential.
     """
     speed_ms = math.hypot(vx, vy) * max_linear
@@ -56,12 +52,7 @@ def velocity_to_wheels(vx, vy, h, max_linear, wheel_radius, max_wheel_omega,
 
 def heading_speed_to_wheels(heading, speed_motor, h, max_wheel_omega,
                             k_turn=4.0):
-    """Sheep variant: speed already expressed in motor (wheel rad/s) units.
-
-    Matches the existing sheep controller (``controllers/sheep/sheep.py``)
-    where ``speed = max(WANDER_SPEED, min(FLEE_SPEED, mag * 3.0))`` and
-    these constants are wheel angular velocities, not linear m/s.
-    """
+    """Sheep variant: speed in wheel rad/s, target as a heading angle."""
     err = math.atan2(math.sin(heading - h), math.cos(heading - h))
     fwd = max(0.0, math.cos(err)) * speed_motor
     turn = k_turn * err