Categories for Development

Offroad Speeder v02

July 17, 2012 by

I updated the version of the Speeder with the CarSmoothFollow Script from the Unity Wiki.

I also added detachable spoilers via the Hinge Joints (setting the Limits very narrow so that they don’t move by themselves). The Fixed Joints seemed a good idea at first but they wouldn’t keep still. So to prevent the spoilers from wobbeling around I used the Hinge Joints instead.

I also tweaked the physics a little bit more but without getting significantly better handling from the car…

Speeder v02

Basic Car Setup

June 26, 2012 by

My current findings for setting up a car rig have been the following:

As we usually deal with several wheels I use arrays to store everything. This lets me add more wheels without breaking into a sweat or having to go copy-paste all over the place.

The base vehicle Axis contains four wheel axis objects that have the WheelColliders. Parented to these we find the wheel meshes. To link these up to the script we have to add these definitions.

public Transform[] wheels;
public WheelCollider[] colliders;
public float[] powers;
public float[] brakes;
public float[] rotations;
public Transform[] steerings;
public Transform centerOfMass;

wheels is for the mesh objects
colliders is for the wheelcolliders
powers is for the amount of torque we apply to each wheel
brakes is for the amount of brakes we apply to each wheel
rotations is for the rotation ratio that is applied to each wheel
steerings is for the amount of steering we apply to each wheel
centerOfMass defines the center of gravity

I set all the WheelCollider settings via script. You can also do this in the inspector, which is much more convinient since you are now able to edit all wheels at one, but in earlier versions you had to do this for every wheel individually.

void Start () {
rigidbody.centerOfMass = centerOfMass.localPosition;

JointSpring suspensionSpring = new JointSpring();
suspensionSpring.spring = 2048.0F;
suspensionSpring.damper = 16.0F;
suspensionSpring.targetPosition = 0.0F;

WheelFrictionCurve forwardFriction = new WheelFrictionCurve();
forwardFriction.extremumSlip = 2.0F;
forwardFriction.extremumValue = 1024.0F;
forwardFriction.asymptoteSlip = 4.0F;
forwardFriction.asymptoteValue = 512.0F;
forwardFriction.stiffness = 1.0F;

WheelFrictionCurve sidewaysFriction = new WheelFrictionCurve();
sidewaysFriction.extremumSlip = 8.0F;
sidewaysFriction.extremumValue = 128.0F;
sidewaysFriction.asymptoteSlip = 16.0F;
sidewaysFriction.asymptoteValue = 64.0F;
sidewaysFriction.stiffness = 1.0F;

for (int i = 0; i < colliders.Length; i++) { colliders[i].suspensionDistance = 1.0F; colliders[i].suspensionSpring = suspensionSpring; colliders[i].forwardFriction = forwardFriction; colliders[i].sidewaysFriction = sidewaysFriction; } }

I first have to define the JointSpring, which defines how much the wheel colliders will bounce. Usually you'll want to set everything to "0" and then increase the spring value until the car stays up by itself. This is very dependant on the number of wheels and the weight of the car. Then set the damper until the car stops bouncing.

The WheelFrictionCurves are a bit more difficult. They will usually define when the wheels will start to spin (forwardFriction) and when the car begins to slide (sidewaysFriction). I still haven't found a good method to set these up right but usually you'll want to set the extremumValue to a force value where you want the car to skid and then set the asymptoteValue to a value of force or grip that you want to have when the wheels have begun to slide.

Finally the values are applied to each individual WheelCollider including the suspensionDistance, which defines how far down the suspension will travel when the wheels are not touching the ground.

Next are the physics calculcations which take place in the FixedUpdate function because these have to run at a constant rate, independant of the frame rate.

void FixedUpdate() {
float speed = Vector3.Magnitude(rigidbody.velocity);
float rpm = (colliders[0].rpm + colliders[1].rpm) / 2.0F;
float torque = 0.0F;
float brake = 0.0F;
float throttle = Input.GetAxis("Vertical");
float steering = Input.GetAxis("Horizontal");
float steering_magnitude = speed;
float steering_range = 45.0F;

if (throttle > 0.0F) {
torque = throttle;
} else if (throttle < 0.0F) { brake = Mathf.Abs(throttle); }

if (steering_magnitude > 0.0F) {
float ratio = steering_magnitude / 45.0F;
steering_range *= 1.0F - ratio;
steering_range = Mathf.Clamp(steering_range, 15.0F, 45.0F);

speed gets the velocity of the car
rpm gets the rpm values from the front wheels
throttle reads the throttle input from the player
torque torque applied by the player
brake brakes applied by the player
steering amount of steering applied by the player
steering_magnitude controls the amount of steering and is decreased at higher speeds to prevent the car from rolling over
steering_range maximum steering angle

for (int i = 0; i < steerings.Length; i++) { steerings[i].localEulerAngles = new Vector3(0.0F, steering * steering_range, 0.0F); }
for (int i = 0; i < colliders.Length; i++) { colliders[i].motorTorque = torque * powers[i]; colliders[i].brakeTorque = brake * brakes[i]; wheels[i].Rotate(colliders[i].rpm * rotations[i] * Time.deltaTime,0 ,0); UpdateWheelHeight(wheels[i], colliders[i]); }
rigidbody.AddForce(Vector3.down * downforce * Vector3.Magnitude(rigidbody.velocity));

Apply steering to the wheels (by multiplying these with the array values I can freely set up steering of the wheels in the front or of all wheels or even only the back wheels

Then apply the throttle and/or brake forces to all wheels, again multiplying these with the array values to switch between FWD / RWD / 4WD, and even braking can be set up to equal the usual 60% front / 40% rear braking force

The visible wheel meshes don't realy contribute to the simulation but are necessary for the player to see what's going on. Therefore the rotation values for the wheels are somewhat approximated. I haven't yet found a reliable calculation example for this allthough I am almost certain there should be one. Simple experiment for the time beeing.

Last but not least the function that sets the wheel height. This was taken from some other example I currently don't remember - probably the official Unity car tutorial.

void UpdateWheelHeight(Transform wheelTransform, WheelCollider collider) {
Vector3 localPosition = wheelTransform.localPosition;
WheelHit hit = new WheelHit();
// see if we have contact with ground
if (collider.GetGroundHit(out hit)) {
// calculate the distance between current wheel position and hit point, correct
// wheel position
localPosition.y -= Vector3.Dot(wheelTransform.position - hit.point, transform.up) - collider.radius;
} else {
// no contact with ground, just extend wheel position with suspension distance
localPosition = -Vector3.up * collider.suspensionDistance;
// actually update the position
wheelTransform.localPosition = localPosition;

There's also a good thread in the Unity forums which deals with adding anti rollbars to the simulation. I removed these again since they didn't improve the handling in later tests of the setup and I wanted to eliminate factors that may make the handling unstable. There'll probably be setups where these anti rollbars serve a usefull purpose:

Unity Forum - anti rollbars

Offroad Speeder

June 25, 2012 by

I’ve experimented with an offroad vehicle, based on the experiences gained with the truck. The basic setup wasn’t too difficult and even jumping and speeding over the rough terrain was pretty nice, but trying to point the car in the right direction or even getting it through the poles grew into quite a challenge because the car slips away much to easily. I’m not sure this can be fixed with simple adjustments to the wheel friction curves.

In it’s normal state the car reacts wonderfully. It accellerates, with little wheel spin, the suspension reacts accordingly. When going into a turn the car begins to slip smoothly outwards, drifting nicely. When going on rough terrain the car jumps an, naturally, is unsteerable while the wheels are airborne. The trouble starts when the car slams onto the ground or is pressed onto the terrain, as it increases its pressure. Somehow the wheel friction curves lose control and the back of the car brakes away violently – sometimes even instantly. I do guess that this is an intended behaviour, but the result leads to an uncontrollable car (most of the time – if a certain speed is reached) and this is not what I had in mind for a fun offroader.

Another challenge was proposed with the following camera. The usual smooth following camera script has the problem that the camera is unable to maintain a fixed distance to the vehicle. My current attempt locks the camera behind the car and smooths out the vertical position. It’s nice but the camera tends to lose the car from view if it goes into a dip… ah well, that’ll also require improvements.

Speeder v01

Improved Trucking Physics

June 7, 2012 by

Had another go at the WheelCollider, as I wasn’t convinced that completely custom built vehicle physics would save that much time, and I have made a couple of improvements. Most of all the Suspension is now correct, as I was doing it wrong most of the time:

  • The best way to start is to set “Spring”, “Damper” and “Target Position” to zero.
  • Set “Suspension Distance” to the distance you want the wheels to drop when the vehicle is in the air.
  • Set “Spring” to something high (try 10240, depending on the weight and number of wheels of the vehicle) and start the game. Tweak the “Spring” value until the suspension is strong enough to keep the body of the vehicle from hitting the ground.
  • Now set the “Damper” to roughly 1/20 of the “Spring” value and tweak it until the vehicle stops bouncing (depending on how much you like it to bounce)
  • Note that everything you attach to the vehicle as well as the center of mass will affect the suspension behaviour and you will probably have to tweak it all over again

Here’s the new version with the improved settings.

Trucking v02


March 18, 2012 by

iTween must be one of the single most usefull scripts that are available. There is just one thing that makes working with it slightly obscure, because of the way extended options have to be added via the hash table by using the iTween.Hash() function.
iTween.MoveTo(exhibitObject, iTween.Hash(
"position", presenterTransform.position,
"time", reloadDelay,
"islocal", false,
"easetype", iTween.EaseType.easeOutQuad

Realtime Cubemap for Reflections

February 25, 2012 by

A nice script for creating a real time cubemap from an object position for use with a reflection shader to create realtime reflections in Unity. Converted from the JavaScript example. Note: This script requires the Unity Pro license.

using UnityEngine;
using System.Collections;

public class RealtimeCubemap : MonoBehaviour {

    public int cubemapSize = 128;
    public bool oneFacePerFrame = false;
    private Camera cam;
    private RenderTexture rtex;
    private GameObject go;

    void Start() {
        // render all six faces at startup

    void LateUpdate() {
        if (oneFacePerFrame) {
            int faceToRender = Time.frameCount % 6;
            int faceMask = 1 << faceToRender;
        } else {
            UpdateCubemap(63); // all six faces

    void UpdateCubemap(int faceMask) {
        if (!cam) {
            go = new GameObject("CubemapCamera");
            go.hideFlags = HideFlags.HideAndDontSave;
            go.transform.position = transform.position;
            go.transform.rotation = Quaternion.identity;
            cam =;
            cam.farClipPlane = 100; // don't render very far into cubemap
            cam.enabled = false;

        if (!rtex) {    
            rtex = new RenderTexture(cubemapSize, cubemapSize, 16);
            rtex.isCubemap = true;
            rtex.hideFlags = HideFlags.HideAndDontSave;
            renderer.sharedMaterial.SetTexture ("_Cube", rtex);

        cam.transform.position = transform.position;
        cam.RenderToCubemap(rtex, faceMask);

    void OnDisable() {
        DestroyImmediate (cam);
        DestroyImmediate (rtex);

String formatting

February 2, 2012 by

Something small but usefull is the String.Format function, with which you can format your numerical outputs:

using System;
using System.Collections;


// formatted float with three zero padded digits
// in front of the "." and three digits after it.
debugText += String.Format("H{0:000.000}\n", heading);

// formatted int with formats for positive;negative;zero values
debugText += String.Format("S{0:+000;-000; 000}\n", speed);

Calculate intersection between to lines

January 25, 2012 by

Here’s something that will calculate where two lines will intersect. If they don’t intersect then the two resulting vectors will mark the points where both lines are closest together.

/* setup vectors */
 Vector3 l1begin = playerCurrentPosition;
 Vector3 l1end = playerTargetPosition - l1begin;
 Vector3 l2begin = enemyCurrentPosition;
 Vector3 l2end = enemyTargetPosition - l2begin;
/* calculate vectors */
 Vector3 n = Vector3.Cross(l1end, l2end);
 Vector3 u = Vector3.Cross(n, l1begin - l2begin) / Vector3.Dot(n, n);
 Vector3 intersection1 = l1begin - l1end * Vector3.Dot(l2end, u);
 Vector3 intersection2 = l2begin - l2end * Vector3.Dot(l1end, u);
/* draw vectors */
 Debug.DrawRay(l1begin, l1end, Color.cyan);
 Debug.DrawRay(l2begin, l2end, Color.magenta);
 Debug.DrawLine(intersection1, intersection2, Color.white);