A Car with Wheel Joints

The first thing we are going to address in this tutorial is the geometry of our car. It is possible to use any custom made model for the vehicle appearance. Every wheel and the frame will be individual independent nodes in the world, so make sure that your vehicle model includes separate meshes for the wheels and the frame.

Right now we are going to take the vehicle model from the content addon included in the SDK and then add some physical parameters to the geometry to achieve a viable driving simulation.

1. Let's create an empty C# project.

2. Install the Eastern European Countryside add-on (available via UNIGINE SDK Browser in the Add-Ons section) and add it to your project by clicking Other Actions -> Configure Project -> Add-ons in the My Projects section of UNIGINE SDK Browser. Drag it into the In Use field and click OK.

   

3. Launch the Editor via the Open Editor button. For your vehicle you can choose any of the minibus nodes located in data/countryside/minibus or import your own model in any supported file format.

   

   A minibus vehicle model has the body frame as the parent node and its wheels as child nodes.

   

4. In the Asset Browser, right-click on a minibus node you like the most and choose Place as Node Content. Place the vehicle on the ground in the world. As we don't plan to use multiple instances of the car, we simply put all its parts directly to the scene, without the NodeReference container.

   

Let’s create a camera for a third-person view. While the camera follows the car, the player can control the viewing direction (rotate the camera) with the mouse. To achieve this, perform the following:

1. In the World Nodes window, delete the first_person_controller containing the default camera.
2. Create a custom Persecutor Camera to follow the car. Go to Create -> Camera -> Persecutor and then place it near the vehicle.
3. Check the Main Player option in the Parameters tab of the PlayerPersecutor to make it the default camera in the world.

4. Delete the default Persecutor_Target node from the World Nodes window hierarchy and set our minibus as the target node for the PlayerPersecutor camera instead.

   

5. To put the camera closer to the vehicle, set the Max Distance parameter for the PlayerPersecutor to 8.

6. You can press the F5 or Run button in the Editor to test out the resulting camera behavior.

   

Now let’s create a C# component to implement driving and steering functionality for the car. To achieve this, do the following:

1. In Asset Browser, right-click and select Create Code -> C# Component. Name it Car, assign it to the minibus node and then double-click on the newly created component to open it in an IDE.

   

2. Get references to joints from the wheel nodes and define variables for the velocity, acceleration and torque values.

   Car.cs

   Source code (C#)

   using System;
   using System.Collections;
   using System.Collections.Generic;
   using Unigine;
   
   [Component(PropertyGuid = "AUTOGENERATED_GUID")] // <-- this line is generated automatically for a new component
   public class Car : Component
   {
   	// driving parameters
   	public float acceleration = 50.0f;
   	public float max_velocity = 90.0f;
   	private float max_turn_angle = 30.0f;
   
   	// nodes with the joints
   	public Node wheel_bl = null;
   	public Node wheel_br = null;
   	public Node wheel_fl = null;
   	public Node wheel_fr = null;
   
   	// camera class
   	public Player player = null;
   
   	// wheel joints
   	private JointWheel joint_wheel_bl = null;
   	private JointWheel joint_wheel_br = null;
   	private JointWheel joint_wheel_fl = null;
   	private JointWheel joint_wheel_fr = null;
   
   	// settings of input controls 
   	private Controls controls = null;
   
   	// current driving parameters
   	private float current_velocity = 0.0f;
   	private float current_torque = 0.0f;
   
   	private void Init()
   	{
   		// get the wheel joints from the nodes
   		if (wheel_bl)
   			joint_wheel_bl = wheel_bl.ObjectBody.GetJoint(0) as JointWheel;
   
   		if (wheel_br)
   			joint_wheel_br = wheel_br.ObjectBody.GetJoint(0) as JointWheel;
   
   		if (wheel_fl)
   			joint_wheel_fl = wheel_fl.ObjectBody.GetJoint(0) as JointWheel;
   
   		if (wheel_fr)
   			joint_wheel_fr = wheel_fr.ObjectBody.GetJoint(0) as JointWheel;	
   
   		// get the settings of input controls relevant to the player (camera)
   		if (player)	
   			controls = player.Controls;	
   	}
   
   }

3. Then add control inputs processing to determine the current torque and velocity to be applied to wheel joints.

   Car.cs

   Source code (C#)

   private void Update()
   {
   	// get the time it took to render the previous frame
   	float deltaTime = Game.IFps;
   
   	current_torque = 0.0f;
   
   	// process control inputs
   	if (controls)
   	{
   
   		// set the torque and increase the current velocity if the forward button is pressed
   		if (controls.GetState(Controls.STATE_FORWARD) != 0)
   		{
   			current_torque = default_torque;
   			current_velocity = MathLib.Max(current_velocity, 0.0f);
   			current_velocity += deltaTime * acceleration; 
   		}
   		// set the torque and decrease the current velocity if the backward button is pressed
   		else if (controls.GetState(Controls.STATE_BACKWARD) != 0) 
   		{
   			current_torque = default_torque;
   			current_velocity = MathLib.Min(current_velocity, 0.0f);
   			current_velocity -= deltaTime * acceleration; 
   		}
   		// exponentially decrease the current velocity when neither throttle nor brakes are applied
   		else
   		{
   			current_velocity *= MathLib.Exp(-deltaTime);
   		}
   
   	}
   
   }

4. To move the car forward or backward, we are going to use joint motors of the front wheels:

   • Setting a positive velocity value will move our car forward.
   • Setting a negative velocity value will move our car backward.

   Each physics frame, we apply current angular velocity and torque to the wheel joints based on the user input.

   Car.cs

   Source code (C#)

   // actually apply the torque and velocity to the front wheel joints
   private void UpdatePhysics()
   {
   	joint_wheel_fl.AngularVelocity = current_velocity;
   	joint_wheel_fr.AngularVelocity = current_velocity;
   
   	joint_wheel_fl.AngularTorque = current_torque;
   	joint_wheel_fr.AngularTorque = current_torque;
   }

To provide the ability to turn left or right as well as the ability to slow down with brakes, we shall implement some additional logic that turns the front wheels and stops the rear ones. To achieve this, do the following:

1. Add the following code to the Car component to add the front wheels turning and braking support.

   Car.cs

   Source code (C#)

   public float turn_speed = 50.0f;
   public float default_torque = 5.0f;  
   public float car_base = 3.0f;
   public float car_width = 2.0f;
   
   private float current_turn_angle = 0.0f;
   
   private void Update()
   {
   	// get the time it took to render the previous frame
   	float deltaTime = Game.IFps;
   
   	current_torque = 0.0f;
   
   	// process control inputs
   	if (controls)
   	{
   
   		/*...*/
   		// turn the front wheels based on the direction input
   		if (controls.GetState(Controls.STATE_MOVE_LEFT) != 0)
   			current_turn_angle += deltaTime * turn_speed;
   		else if (controls.GetState(Controls.STATE_MOVE_RIGHT) != 0)
   			current_turn_angle -= deltaTime * turn_speed;
   		else
   		{
   			// get rid of the front wheel wiggle
   			if (MathLib.Abs(current_turn_angle) < 0.25f)
   				current_turn_angle = 0.0f;
   
   			// align the front wheels if there are no more direction input
   			current_turn_angle -= MathLib.Sign(current_turn_angle) * turn_speed * deltaTime;
   		}
   
   		// apply braking by maxing out the angular damping if the brake button is pressed
   		if (controls.GetState(Controls.STATE_USE) != 0)
   		{
   			joint_wheel_bl.AngularDamping = 10000.0f;
   			joint_wheel_br.AngularDamping = 10000.0f;
   		}
   		else
   		{
   			joint_wheel_bl.AngularDamping = 0.0f;
   			joint_wheel_br.AngularDamping = 0.0f;
   		}
   
   	}
   
   	// clamp the velocity and the front wheels turn angle
   	current_velocity = MathLib.Clamp(current_velocity, -max_velocity, max_velocity);
   	current_turn_angle = MathLib.Clamp(current_turn_angle, -max_turn_angle, max_turn_angle);
   
   	// figure out the correct turn angle for the front wheels
   	float angle_0 = current_turn_angle;
   	float angle_1 = current_turn_angle;
   	if (MathLib.Abs(current_turn_angle) > MathLib.EPSILON)
   	{
   		float radius = car_base / MathLib.Tan(current_turn_angle * MathLib.DEG2RAD);
   		float radius_0 = radius - car_width * 0.5f;
   		float radius_1 = radius + car_width * 0.5f;
   
   		angle_0 = MathLib.Atan(car_base / radius_0) * MathLib.RAD2DEG;
   		angle_1 = MathLib.Atan(car_base / radius_1) * MathLib.RAD2DEG;
   	}
   
   	joint_wheel_fr.Axis10 = MathLib.RotateZ(angle_1).GetColumn3(0);
   	joint_wheel_fl.Axis10 = MathLib.RotateZ(angle_0).GetColumn3(0);
   
   }

2. In the Editor, assign wheels (ObjectMeshStatic nodes) and the camera (PlayerPersecutor node) to the corresponding fields of the Car component as specified below.

   

Congratulations! Now you can finally drive the car around the world. If the current physics of the car is not suitable for your needs, you can always fine tune the parameters of the wheel joints and achieve the results you need. Also, see the Basic Programming How-To Livestream for the hands-on vehicle implementation and discussions. The full source code of the Car component is given below.

using System;
using System.Collections;
using System.Collections.Generic;
using Unigine;

[Component(PropertyGuid = "AUTOGENERATED_GUID")] // <-- this line is generated automatically for a new component
public class Car : Component
{
	// driving parameters
	public float acceleration = 50.0f;
	public float max_velocity = 90.0f;
	private float max_turn_angle = 30.0f;

	public float turn_speed = 50.0f;
	public float default_torque = 5.0f;  
	public float car_base = 3.0f;
	public float car_width = 2.0f;

	// nodes with the joints
	public Node wheel_bl = null;
	public Node wheel_br = null;
	public Node wheel_fl = null;
	public Node wheel_fr = null;

	// camera class
	public Player player = null;

	// wheel joints
	private JointWheel joint_wheel_bl = null;
	private JointWheel joint_wheel_br = null;
	private JointWheel joint_wheel_fl = null;
	private JointWheel joint_wheel_fr = null;

	// settings of input controls 
	private Controls controls = null;

	// current driving parameters
	private float current_velocity = 0.0f;
	private float current_torque = 0.0f;

	private float current_turn_angle = 0.0f;

	private void Init()
	{
		// get the wheel joints from the nodes
		if (wheel_bl)
			joint_wheel_bl = wheel_bl.ObjectBody.GetJoint(0) as JointWheel;

		if (wheel_br)
			joint_wheel_br = wheel_br.ObjectBody.GetJoint(0) as JointWheel;

		if (wheel_fl)
			joint_wheel_fl = wheel_fl.ObjectBody.GetJoint(0) as JointWheel;

		if (wheel_fr)
			joint_wheel_fr = wheel_fr.ObjectBody.GetJoint(0) as JointWheel;	

		// get the settings of input controls relevant to the player (camera)
		if (player)	
			controls = player.Controls;	
	}

	private void Update()
	{
		// get the time it took to render the previous frame
		float deltaTime = Game.IFps;

		current_torque = 0.0f;

		// process control inputs
		if (controls)
		{

			// set the torque and increase the current velocity if the forward button is pressed
			if (controls.GetState(Controls.STATE_FORWARD) != 0)
			{
				current_torque = default_torque;
				current_velocity = MathLib.Max(current_velocity, 0.0f);
				current_velocity += deltaTime * acceleration; 
			}
			// set the torque and decrease the current velocity if the backward button is pressed
			else if (controls.GetState(Controls.STATE_BACKWARD) != 0) 
			{
				current_torque = default_torque;
				current_velocity = MathLib.Min(current_velocity, 0.0f);
				current_velocity -= deltaTime * acceleration; 
			}
			// exponentially decrease the current velocity when neither throttle nor brakes are applied
			else
			{
				current_velocity *= MathLib.Exp(-deltaTime);
			}

			/*...*/
			// turn the front wheels based on the direction input
			if (controls.GetState(Controls.STATE_MOVE_LEFT) != 0)
				current_turn_angle += deltaTime * turn_speed;
			else if (controls.GetState(Controls.STATE_MOVE_RIGHT) != 0)
				current_turn_angle -= deltaTime * turn_speed;
			else
			{
				// get rid of the front wheel wiggle
				if (MathLib.Abs(current_turn_angle) < 0.25f)
					current_turn_angle = 0.0f;

				// align the front wheels if there are no more direction input
				current_turn_angle -= MathLib.Sign(current_turn_angle) * turn_speed * deltaTime;
			}

			// apply braking by maxing out the angular damping if the brake button is pressed
			if (controls.GetState(Controls.STATE_USE) != 0)
			{
				joint_wheel_bl.AngularDamping = 10000.0f;
				joint_wheel_br.AngularDamping = 10000.0f;
			}
			else
			{
				joint_wheel_bl.AngularDamping = 0.0f;
				joint_wheel_br.AngularDamping = 0.0f;
			}

		}

		// clamp the velocity and the front wheels turn angle
		current_velocity = MathLib.Clamp(current_velocity, -max_velocity, max_velocity);
		current_turn_angle = MathLib.Clamp(current_turn_angle, -max_turn_angle, max_turn_angle);

		// figure out the correct turn angle for the front wheels
		float angle_0 = current_turn_angle;
		float angle_1 = current_turn_angle;
		if (MathLib.Abs(current_turn_angle) > MathLib.EPSILON)
		{
			float radius = car_base / MathLib.Tan(current_turn_angle * MathLib.DEG2RAD);
			float radius_0 = radius - car_width * 0.5f;
			float radius_1 = radius + car_width * 0.5f;

			angle_0 = MathLib.Atan(car_base / radius_0) * MathLib.RAD2DEG;
			angle_1 = MathLib.Atan(car_base / radius_1) * MathLib.RAD2DEG;
		}

		joint_wheel_fr.Axis10 = MathLib.RotateZ(angle_1).GetColumn3(0);
		joint_wheel_fl.Axis10 = MathLib.RotateZ(angle_0).GetColumn3(0);

	}

	// actually apply the torque and velocity to the front wheel joints
	private void UpdatePhysics()
	{
		joint_wheel_fl.AngularVelocity = current_velocity;
		joint_wheel_fr.AngularVelocity = current_velocity;

		joint_wheel_fl.AngularTorque = current_torque;
		joint_wheel_fr.AngularTorque = current_torque;
	}

}