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Vivek Tank

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  1. Objective The main objective of this post is to give an idea of how to work with wheel collider and physics of Wheel Collider. Want to Make a Car Racing Game? Having troubles with Car Physics? Where to use Wheel Collider? How to use Wheel Collider? What are the components of Wheel Collider? How is Wheel Collider Different than other Colliders? Have these Questions in Your Mind? No worries... You'll know everything about Wheelcollider after reading this post. INTRODUCTION Wheel Collider is a special kind of Collider which is used for vehicles. It has in built collision detection technique and physics of actual Wheel. It can be used for objects other than wheels (like bumper Boats, bumper cars etc which uses suspension force ), but it is specially designed for vehicles with wheels. Is there is anything special which is not in other Colliders? Yes, each and every collider has something special (That’s why Unity created them). In this Collider, you will get all the components which are used to make vehicle drivable. Do have any idea about components..? No problem, I will explain components here. Before that, it's very important to understand how the Wheel Collider component works internally, to get a car working in Unity Here, I have explained everything. This is how you look at your dashing and shiny car. But, Unity doesn’t have good eyesight. So Unity looks at your car like this. 4 wheels colliders and 1 car collider, that’s it! Now Let’s Discover inside Wheel Collider. Wheel doesn’t have any shape it is Raycast based. Mass & Radius: mass and radius of the wheel. (Easy isn’t it ?) Below I had given a little introduction about physics of wheel collider. Every Wheel counts it’s sprung mass. Sprung mass (not weight) is used to apply individual force on each wheel. Suspension Distance is the distance between max droop and max compression. This suspension is calculated based on rest pose. Suspension Force(F) = (sprungMass * g ) +( jounce * stiffness) - (damper * jounceSpeed) jounce -> offset of the wheel relative to the rest pose. stiffness -> that means physics friction. (setting this to 0 means no friction change this runtime to simulate in various ground material). damper -> damping value applied to the wheel jounceSpeed -> wheel moved with suspension travel direction. Tire simulation rather than using dynamic or static material slip-based material is used. To learn more about physics of wheel collider click here First we need to setup Scene for that (Don’t Worry that is Easy part). PART-1: SCENE SETUP Step 1: Create a 3D plane Object give it scale of (100, 0, 100). Step 2: Create an empty Object add Rigidbody 3D. Name it as “Car” Step 3: Import 3D Car Model inside your Scene (you will get download link below) add as a child of Car. Step 4: Take Mesh Collider and add as a child of Car name it ”CarCollider”. Step 5: Create Two empty GameObject inside Car name them as “Wheel Meshed ” and “Wheel Collider”. Step 6: Inside Wheel Meshes add 4 empty GameObject name them as “FL” ,”FR” ,”RL” and “RR”. assign Mesh of Wheel (you will get download link below). Set their Position. Step 7: Inside Wheel Collider add 4 empty GameObjects name them as “Col_FL” ,”Col_FR”, ”Col_RL” and “Col_RR”. Add wheel collider as their component. Set radius of colliders same as the size of mesh and set their position same as the mesh have. Yeap, Its Done! actually that was the Difficult part to setup scene. Now Time for really easy part Scripting. PART-2: SCRIPTING (Check Script Reference Click here) [System.Serializable] public class AxleInfo { public WheelCollider leftWheelCollider; public WheelCollider rightWheelCollider; public GameObject leftWheelMesh; public GameObject rightWheelMesh; public bool motor; public bool steering; } In this AxleInfo Class, we are going to store info for a pair of the wheel. Variable Name Variable Type Description leftWheelCollider / rightWheelCollider WheelCollider To drive a car using WheelColliders inbuilt physics. leftWheelMesh / rightWheelMesh GameObject To Visualize rotation and movement of wheels. motor bool Enable movement of this pair of wheels. steering bool Enable rotation of this pair of wheels. Now, Let's go for long drive . This script is to drive Car. public class CarDriver : MonoBehaviour { public List<AxleInfo> axleInfos; public float maxMotorTorque; public float maxSteeringAngle; public float brakeTorque; public float decelerationForce; public void ApplyLocalPositionToVisuals (AxleInfo axleInfo) { Vector3 position; Quaternion rotation; axleInfo.leftWheelCollider.GetWorldPose (out position, out rotation); axleInfo.leftWheelMesh.transform.position = position; axleInfo.leftWheelMesh.transform.rotation = rotation; axleInfo.rightWheelCollider.GetWorldPose (out position, out rotation); axleInfo.rightWheelMesh.transform.position = position; axleInfo.rightWheelMesh.transform.rotation = rotation; } void FixedUpdate () { float motor = maxMotorTorque * Input.GetAxis ("Vertical"); float steering = maxSteeringAngle * Input.GetAxis ("Horizontal"); for (int i = 0; i < axleInfos.Count; i++) { if (axleInfos [i].steering) { Steering (axleInfos [i], steering); } if (axleInfos [i].motor) { Acceleration (axleInfos [i], motor); } if (Input.GetKey (KeyCode.Space)) { Brake (axleInfos [i]); } ApplyLocalPositionToVisuals (axleInfos [i]); } } private void Acceleration (AxleInfo axleInfo, float motor) { if (motor != 0f) { axleInfo.leftWheelCollider.brakeTorque = 0; axleInfo.rightWheelCollider.brakeTorque = 0; axleInfo.leftWheelCollider.motorTorque = motor; axleInfo.rightWheelCollider.motorTorque = motor; } else { Deceleration (axleInfo); } } private void Deceleration (AxleInfo axleInfo) { axleInfo.leftWheelCollider.brakeTorque = decelerationForce; axleInfo.rightWheelCollider.brakeTorque = decelerationForce; } private void Steering (AxleInfo axleInfo, float steering) { axleInfo.leftWheelCollider.steerAngle = steering; axleInfo.rightWheelCollider.steerAngle = steering; } private void Brake (AxleInfo axleInfo) { axleInfo.leftWheelCollider.brakeTorque = brakeTorque; axleInfo.rightWheelCollider.brakeTorque = brakeTorque; } } I know, this script was a little bit difficult but I am here to help you. Variable Name Variable Type Description axleInfos List List of AxleInfo Which contains a pair of wheels data. maxMotorTorque float maximum Torque is applicable on Vehicle. maxSteeringAngle float Maximum angle at which wheel is rotate. brakeTorque float Torque is applied when a brake is pressed. decelerationForce float This force is applied to stop the vehicle because of friction. ApplyLocalPositionToVisuals (AxleInfo axleInfo) This Method takes one argument: axleInfo. This method is used to Display rotation and position of WheelMeshes. FixedUpdate() This is Unity callBack used to do certain changes in physics at fixed time. Inside that, we will take Input. Vertical: W/Up Arrow for Forward & S/Down Arrow for Backward. Horizontal: A/Left Arrow for Left Side Rotation. & D/Right Arrow for Right Side Rotation. Space: To Stop(brake). Assign this Script to our “Car” GameObject. Add Size of AxleInfo to 2. Now add your Colliders and Meshes to appropriate Location. We have 3 methods to Control Car Acceleration(), Steering() and Brake(). You can relate all the methods listed below. These methods are works like how actually Vehicle we drive in reality Accelerator, Brake(No Clutch here). Acceleration() It is used to make the vehicle move forward and backward. If forward or backward buttons are not clicked then need to add Deceleration(). motorTorque is used to add torque (In forward or backward direction) in a vehicle. When the vehicle is moving at that time brakeTorque is needed to change to 0. Deceleration() It is used to stop the vehicle when forward and backward buttons are not pressed. Steering() It is used to turn angle of vehicle. steerAngle is used to change an angle of the the vehicle Brake() It is used to stop the vehicle using brakeTorque property. PART-3: ASSIGNING VALUES Finally at the end, This is the last thing to make your car drivable. Enable motor if you want to Apply Force and Suspension on That Wheel. Enable Steering if you want to give rotation Force on that Wheel. Maximum Motor Torque change as per your car’s Rigidbody mass. Maximum Steering Angle must be between (30-35). Brake Torque depends on how much Brake Torque you want to apply. Deceleration Force is must be less than Brake Torque. Tip Experiment with This Value to make your Car run smoothly. Caution Brake Torque and Deceleration Force value need to be much higher to stop usually(1e+5 to 1e+8).
  2. This article provides a brief introduction to creating Homing Missiles in a 2D game. A Homing Missile is a missile that locks onto and chases a target until it reaches the target and explodes. We'll be using the Unity engine, and a script for the Homing missile is also included and explained in the article. Scene Setup Create two 2D Objects named “Missile ” and “Target” Add a sprite to these 2D Objects (You can download the project from below link) Add rigidBody 2D in missile and add Script also name it as ”Homing Missile” Implementation To implement a basic homing missile we could use MoveToward/Lerp until the missile reaches its target. Using MoveToward/Lerp, the missiong will reach the target properly, but its movement will be very linear - there is no feel of a homing missile. To implement a better feel, we need to simulate with better physics. Let's walk through a solution: public class HomingMissile : MonoBehaviour { public Transform target; public Rigidbody2D rigidBody; public float angleChangingSpeed; public float movementSpeed; void FixedUpdate() { Vector2 direction = (Vector2)target.position - rb.position; direction.Normalize (); float rotateAmount = Vector3.Cross (direction, transform.up).z; rigidBody.angularVelocity = -angleChangingSpeed * rotateAmount; rigidBody.velocity = transform.up * movementSpeed; } } Variables rigidBody: rigidBody of the missile to add velocity and change angle. target: To get the position of the Target. angleChangingSpeed: The speed to change the angle movementSpeed: Speed of movement The Math Here is a visualization of the path our homing missile needs to take on a moving target. Let's talk about how to implement this. First, you need “Direction”. Step 1 We subtract the two vectors, targetPosition and missilePosition to get the direction. direction= targetPosition (target.position) - missilePosition(rb.position); Step 2 We convert the direction vector to a unit vector through normalization. direction.Normalize(); Step 3 Calculate the rotation vector. The rotation vector will be the cross product of our direction vector and our missile's up vector. The rotation vector will be the z-axis of the cross product. In the diagram below the blue arrow is our direction, the red arrow is the up vector of our missile's transform, and the green arrow is our resulting z-axis component of the cross product between direction and up. float rotateAmount=Vector3.Cross(direction,transform.up).z; Step 4 Next, we change the angularVelocity of the missile's rigidBody to control the orientation of our missile. We use an angleChangingSpeed factor to control the speed of rotation. rb.angularVelocity = -angleChangingSpeed * rotationAmount Step 5 And finally we add velocity to our rigidBody, which controls the translation of our missile in the environment. rb.velocity = tranform.up * movementSpeed But wait... We aren't done yet. In the code above we have two movement factors that need to be balanced: angleChangingSpeed and movementSpeed. In the above Image, the missile is moving toward the target, there is no problem here. However, in this image we have one tick of the simulation and the target has moved to a new position. The missile is oriented toward the target due to angular velocity (red), but it continues to move toward the target's previous position due to its velocity (black). As we can see, the missile's velocity moves it behind the target (black) while the angular velocity (red) tries to pull the missile to the target. This can result in the missile falling into a stable orbit around the target and never reaching its goal. We can balance this with the angleChangingSpeed and movementSpeed parameters. There is no particular formula to balance these parameters. The necessary parameters will depend on your gameplay and game design. Be careful with extremes for movementSpeed, positive or negative. Too slow and your missiles won't feel like homing missiles, and too fast will lead to them being trapped in orbit. Same with angleChangingSpeed. Too small it will be in orbit, and too high you will lose the feel of homing missiles. I hope this article has been useful and hope to see homing missiles in your game!
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