Customize vehicle slip due to road surfaces

Assets/AWSIM/Scripts/Vehicles/GroudSlipMultiplier.cs

@@ -0,0 +1,25 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+namespace AWSIM
+{
+    /// <summary>
+    /// By attaching this script to a collider whose IsTrigger is On, the slip rate of the Vehicle can be changed. 1 no slip, 0 is full slip.
+    /// </summary>
+    public class GroudSlipMultiplier : MonoBehaviour
+    {
+        [Range(0, 1)] [SerializeField] float forwardSlip;
+        [Range(0, 1)] [SerializeField] float sidewaySlip;
+
+        /// <summary>
+        /// Slip multiplier in foward direction.
+        /// </summary>
+        public float FowardSlip => forwardSlip;
+
+        /// <summary>
+        /// Slip multiplier in sideway direction.
+        /// </summary>
+        public float SidewaySlip => sidewaySlip;
+    }
+}

Assets/AWSIM/Scripts/Vehicles/Vehicle.cs

@@ -114,6 +114,40 @@ public class Axle
         // reference sample (in 1998): https://www.researchgate.net/publication/228945609_Measured_Vehicle_Inertial_Parameters-NHTSA
         [SerializeField] Vector3 inertia;
 
+        /// <summary>
+        /// Change the slip rate of the wheel in the foward direction of this car. 1 no slip, 0 is full slip.
+        /// </summary>
+        public float ForwardSlipMultipler
+        {
+            get
+            {
+                return wheels[0].ForwardSlipMultiplier;
+            }
+
+            set
+            {
+                foreach (var e in wheels)
+                    e.ForwardSlipMultiplier = value;
+            }
+        }
+
+        /// <summary>
+        /// Change the slip rate of the wheel in the sideway direction of this car. 1 no slip, 0 is full slip.
+        /// </summary>
+        public float SidewaySlipMultipler
+        {
+            get
+            {
+                return wheels[0].SidewaySlipMultiplier;
+            }
+
+            set
+            {
+                foreach (var e in wheels)
+                    e.SidewaySlipMultiplier = value;
+            }
+        }
+
         [Header("Physics Settings (experimental)")]
 
         // Threshold for Rigidbody Sleep (m/s).
@@ -254,6 +288,32 @@ void Awake()
             // Set inertia values.
             if (useInertia)
                 m_rigidbody.inertiaTensor = inertia;
+
+            // Initialize with non-slip value
+            ForwardSlipMultipler = 1f;
+            SidewaySlipMultipler = 1f;
+        }
+
+        // GroundSlipMultiplier changes the slip rate.
+        private void OnTriggerEnter(Collider other)
+        {
+            var groundSlipMultiplier = other.GetComponent<GroudSlipMultiplier>();
+            if (groundSlipMultiplier != null)
+            {
+                ForwardSlipMultipler = groundSlipMultiplier.FowardSlip;
+                SidewaySlipMultipler = groundSlipMultiplier.SidewaySlip;
+            }
+        }
+
+        // GroundSlipMultiplier changes the slip rate.
+        private void OnTriggerExit(Collider other)
+        {
+            var groundSlipMultiplier = other.GetComponent<GroudSlipMultiplier>();
+            if (groundSlipMultiplier != null)
+            {
+                ForwardSlipMultipler = 1;       // Default value is 1 if there is no slip.
+                SidewaySlipMultipler = 1;
+            }
         }
 
         void FixedUpdate()

Assets/AWSIM/Scripts/Vehicles/Wheel.cs

@@ -24,6 +24,16 @@ public class Wheel : MonoBehaviour
         /// </summary>
         public bool IsSleep { get; private set; }
 
+        /// <summary>
+        /// Slip multiplier in foward direction.
+        /// </summary>
+        public float ForwardSlipMultiplier { get; set; } = 1;
+
+        /// <summary>
+        /// Slip multiplier in sideway direction.
+        /// </summary>
+        public float SidewaySlipMultiplier { get; set; } = 1;
+
         /// <summary>
         /// Steering angle of the wheel.
         /// </summary>
@@ -71,11 +81,12 @@ void Update()
             // TODO: Determine rotation from the speed of the wheels.
             void UpdateVisual(float speed, float steerAngle)
             {
+                // wheel position
                 wheelCollider.GetWorldPose(out var pos, out _);
                 wheelVisualTransform.position = pos;
 
                 // wheel forward rotation(pitch).
-                var additionalPitchAngle = (speed * Time.deltaTime / wheelCollider.radius) * Mathf.Rad2Deg;
+                var additionalPitchAngle = (speed / ForwardSlipMultiplier * Time.deltaTime / wheelCollider.radius) * Mathf.Rad2Deg;
                 wheelPitchAngle += additionalPitchAngle;
                 wheelPitchAngle %= 360;
 
@@ -141,12 +152,12 @@ public void UpdateWheelForce(float acceleration)
                 return;
 
             // Apply cancel force.
-            var lateralCancelForce = GetSkiddingCancelForce();
+            var lateralCancelForce = GetSkiddingCancelForce() * SidewaySlipMultiplier;
             vehicleRigidbody.AddForceAtPosition(lateralCancelForce, wheelHit.point, ForceMode.Force);
 
             // Apply drive force.
             // Apply a force that will result in the commanded acceleration.
-            var driveForce = acceleration * wheelHit.forwardDir;
+            var driveForce = acceleration * wheelHit.forwardDir * ForwardSlipMultiplier;
             vehicleRigidbody.AddForceAtPosition(driveForce, wheelHit.point, ForceMode.Acceleration);
 
             // Counteracts the sideway force of the tire.

docs/Components/Vehicle/CustomizeSlip/index.md

@@ -0,0 +1,15 @@
+# Customize slip
+
+By attaching a `GroundSlipMutiplier.cs` script to a collider (trigger), you can change the slip of the vehicle within the range of that collider.
+
+## Sample scene
+
+`Assets\AWSIM\Scenes\Samples\VehicleSlipSample.unity`
+
+## How to setup
+
+1. Create collider
+2. Check IsTrigger
+3. Change properties of FowardSlip and SidewaySlip.
+
+![](image.png)

mkdocs.yml

@@ -62,6 +62,7 @@ nav:
         - Add Colliders: Components/Vehicle/AddNewVehicle/AddColliders/index.md
         - Add Sensors: Components/Vehicle/AddNewVehicle/AddSensors/index.md
         - Add Visual Elements: Components/Vehicle/AddNewVehicle/AddVisualElements/index.md
+      - Customize Slip: Components/Vehicle/CustomizeSlip/index.md
       - FollowCamera: Components/Vehicle/FollowCamera/index.md
     - Sensors:
       - LiDAR Sensor: