CarController Class Documentation | Krishnamohan Productions

Overview

The CarController class is responsible for controlling a car's movement, including steering, acceleration, and braking. It interacts directly with Unity’s WheelCollider and Transform components to simulate realistic car physics and update the visual position and rotation of the wheels based on player input.

This script is designed to be beginner-friendly, easy to customize, and suitable for both personal and commercial Unity projects.

🔓 Public Variables

⚙️ Settings

motorForce (float)
The force applied to the car’s motor for acceleration.
Higher values result in faster acceleration.
breakForce (float)
The force applied when the car is braking.
Higher values result in stronger and quicker stopping.
maxSteerAngle (float)
The maximum steering angle of the front wheels.
Higher values allow sharper turns.

🛞 Wheel Colliders

frontLeftWheelCollider (WheelCollider)
WheelCollider for the front-left wheel.
frontRightWheelCollider (WheelCollider)
WheelCollider for the front-right wheel.
rearLeftWheelCollider (WheelCollider)
WheelCollider for the rear-left wheel.
rearRightWheelCollider (WheelCollider)
WheelCollider for the rear-right wheel.

These components handle suspension, friction, and collision physics.

🎨 Wheel Transforms (Visuals)

frontLeftWheelTransform (Transform)
Visual transform of the front-left wheel.
frontRightWheelTransform (Transform)
Visual transform of the front-right wheel.
rearLeftWheelTransform (Transform)
Visual transform of the rear-left wheel.
rearRightWheelTransform (Transform)
Visual transform of the rear-right wheel.

These transforms are updated every physics frame to match the WheelCollider’s position and rotation.

🔒 Private Variables

horizontalInput (float)
Stores player steering input (left / right).
verticalInput (float)
Stores player acceleration input (forward / reverse).
currentSteerAngle (float)
Current steering angle applied to the front wheels.
currentBreakForce (float)
Current braking force applied to all wheels.
isBreaking (bool)
Indicates whether the brake key (Spacebar) is pressed.

🧠 Methods

FixedUpdate()

The main physics update loop, called every physics frame.

It performs the following actions in order:

GetInput()
HandleMotor()
HandleSteering()
UpdateWheels()

GetInput()

Collects player input:

Horizontal axis (Input.GetAxis("Horizontal")) for steering
Vertical axis (Input.GetAxis("Vertical")) for acceleration and reverse
Spacebar (Input.GetKey(KeyCode.Space)) for braking

HandleMotor()

Applies motor torque to the driven wheels based on vertical input.

Applies acceleration or reverse torque
Checks if braking is active
Calls ApplyBreaking() when needed

ApplyBreaking()

Applies brake torque to all WheelColliders when braking is active.

Brake strength is controlled by currentBreakForce
Ensures consistent stopping behavior across all wheels

HandleSteering()

Adjusts the steering angle of the front wheels based on horizontal input.

Steering angle is clamped using maxSteerAngle
Provides smooth and responsive turning

UpdateWheels()

Updates the visual position and rotation of each wheel by calling:

UpdateSingleWheel() for every wheel

UpdateSingleWheel(WheelCollider wheelCollider, Transform wheelTransform)

Synchronizes the visual wheel with its physics collider.

Retrieves wheel position and rotation using GetWorldPose()
Applies them to the corresponding Transform

This ensures accurate visual feedback matching the physics simulation.

📝 Notes & Best Practices

Ensure all WheelCollider components are properly aligned with their visual wheel meshes.
Terrain or road surfaces must have a Collider to prevent wheels from sinking or floating.
This script uses Unity’s default Input Manager axes, making it compatible with:
- Arrow keys
- WASD
- Gamepads / joysticks
The controller is designed as a front-wheel-drive system.
- For rear-wheel or all-wheel drive, apply motor torque to additional WheelColliders.

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