Godot Game Engine Simulation

Author: Lawrence Chan

Overview

Virtual simulation utilizing Godot Game Engine for testing vehicle characteristics / autonomous driving.

Vehicle Controller Script (Godot – VehicleBody3D)

Overview

This script implements a basic vehicle controller for a Godot VehicleBody3D node.

It handles:

• Acceleration and engine force
• Braking
• Steering control
• Natural deceleration
• Speed limiting
• Debug speed output

The script reads player inputs and updates the physics behavior of the vehicle’s VehicleWheel3D nodes accordingly.

Node Requirements

The script must be attached to a VehicleBody3D node.

The vehicle should contain child nodes of type:

• VehicleWheel3D with use_as_traction = true (drive wheels)
• VehicleWheel3D with use_as_steering = true (steering wheels)

Input Controls

These must be mapped in Project Settings → Input Map:

• accelerate
• decelerate
• steer_left
• steer_right
• steer_center

Configuration Constants

Debug

const DISPLAY_DEBUG_SPEED = true

Prints vehicle speed and steering data to the console.

Engine / Acceleration

Braking

Steering

Speed Limit

const MAX_VEHICLE_SPEED_MPH = 90.0

Maximum allowed vehicle speed.

Internally the script uses m/s and km/h, converting to mph only for debug display.

Core Variables

Utility Functions

Degree / Radian Conversion

func deg_to_rad(deg):
    return deg * PI / 180

func rad_to_deg(rad):
    return rad * 180 / PI

Used for steering calculations.

Speed Conversion

func kph_to_mph(kph) -> float:
    return kph / 1.609

Converts kilometers per hour to miles per hour.

Throttle Function

func throttle_function(current_speed) -> float:
    # Connect engine power data here
    return 1000.0

Returns engine force when dynamic throttle is enabled.

This is currently a placeholder and can be replaced with a realistic engine torque curve.

Normalized Steering Angle

func norm_steering_angle(steer: float) -> float:
    return steer * (90/PI)

Converts steering radians into a normalized value for debugging.

Physics Update Loop

Main vehicle logic runs inside:

func _physics_process(delta: float) -> void:

This function performs:

1. Input processing
2. Debug speed calculation
3. Wheel physics updates

Speed Calculation

Vehicle speed is calculated from the body’s velocity:

var velocity_mps = linear_velocity.length()

Conversions:

• m/s → km/h: mps * 3.6
• km/h → mph: kph / 1.609

Example debug output:

VEHICLE SPEED | 72 km/h [20 m/s] (45 mph) | STEER: 0.4

Wheel Processing

The script loops through all child nodes:

for object in get_children():

If the node is a VehicleWheel3D, it is processed depending on its role.

Traction Wheels

If:

wheel.use_as_traction

The script applies engine and braking forces.

Acceleration

Engine force increases while:

• Below MAX_POWER
• Below MAX_VEHICLE_SPEED

Braking

Brake force increases up to:

MAX_BRAKING

Engine force is set to zero when braking.

Natural Deceleration

When neither accelerating nor braking:

• Engine force gradually decreases
• Base braking (BASE_DECEL) is applied

Steering Wheels

If:

wheel.use_as_steering

The script adjusts the wheel steering angle.

Steering changes are converted from degrees to radians because Godot steering uses radians.

Steering Limits

Maximum steering range:

± MAX_STEERING_ANGLE

If exceeded, the value is clamped.

Steering Reset

Pressing C resets steering:

wheel.steering = 0.0

Vehicle Behavior Summary

Possible Improvements

• Implement a realistic engine torque curve
• Add gear ratios and transmission
• Implement traction control
• Add drift or slip simulation
• Display speed using a UI element instead of console output

Example Node Structure

VehicleBody3D
│
├── VehicleWheel3D (FrontLeft)
├── VehicleWheel3D (FrontRight)
├── VehicleWheel3D (RearLeft)
└── VehicleWheel3D (RearRight)

Typical configuration:

Summary

This script provides a basic but functional vehicle physics controller using Godot’s built-in vehicle system.

It demonstrates:

• Player input handling
• Vehicle physics updates
• Wheel-based acceleration and steering
• Debug speed monitoring

The system is designed to be simple, modular, and easily extendable for more advanced driving simulations.