Fix issue that car can't full stop if brake (#786)

Fix issue that car can't full stop if brake=-1

metadrive/component/vehicle/base_vehicle.py

@@ -506,8 +506,19 @@ def _apply_throttle_brake(self, throttle_brake):
                     self.system.applyEngineForce(max_engine_force * throttle_brake, wheel_index)
                     self.system.setBrake(0, wheel_index)
                 else:
-                    self.system.applyEngineForce(0.0, wheel_index)
-                    self.system.setBrake(abs(throttle_brake) * max_brake_force, wheel_index)
+                    DEADZONE = 0.01
+
+                    # Speed m/s in car's heading:
+                    heading = self.heading
+                    velocity = self.velocity
+                    speed_in_heading = velocity[0] * heading[0] + velocity[1] * heading[1]
+
+                    if speed_in_heading < DEADZONE:
+                        self.system.applyEngineForce(0.0, wheel_index)
+                        self.system.setBrake(2, wheel_index)
+                    else:
+                        self.system.applyEngineForce(0.0, wheel_index)
+                        self.system.setBrake(abs(throttle_brake) * max_brake_force, wheel_index)
 
     """---------------------------------------- vehicle info ----------------------------------------------"""
 

metadrive/tests/test_policy/test_full_stop.py

@@ -0,0 +1,43 @@
+from metadrive.envs import MetaDriveEnv
+
+
+def test_full_stop():
+    config = {
+        "use_render": False,
+        "map": "y",
+        "vehicle_config": {
+            "spawn_position_heading": [[10, 10], 0],
+        },
+    }
+
+    env = MetaDriveEnv(config)
+    env.reset()
+
+    try:
+        # Driving forward phase
+        for step in range(30):  # Drive forward for 30 steps
+            env.step([0, 1])  # Full throttle, no steering
+            # print("Speed: ", env.agent.speed)
+            # env.render(mode="topdown")
+
+        success = False
+        print("Starting Brake Phase")
+        for i in range(20):  # Continue braking until the car stops
+            env.step([0.0, -1.0])  # No throttle, apply brake
+            # print(i, "Speed: ", env.agent.speed)
+            # env.render(mode="topdown")
+
+            if env.agent.speed <= 0.01:  # Stop if speed is effectively zero
+                print("Car has stopped.")
+                success = True
+                break
+
+        if not success:
+            raise ValueError("Car did not stop after 20 steps")
+
+    finally:
+        env.close()
+
+
+if __name__ == '__main__':
+    test_full_stop()