Unity3d 汽车物理系统

    

     大家好，认识一下，我叫山西小龙，QQ:1357098586，希望大家能够互相帮助，我的文章偏多与机械方面，呵呵！

     第一篇，就写个物理车的！

          首先，资料的来源!http://www.gotow.net/andrew/wordpress/?page_id=78在这个链接的底部有下载的链接，如果下载不 到，   我可以共享出来！

     第二部，开始一些翻译和讲解！

             1.物理车的碰撞！

            

             其中草绿色线条是车的两个包围盒！四个轮子加了四个车轮碰撞器(WheelCollider);

             2.物理车的层次结构关系

            

            根节点是PlayerCar,Colliders,就是第一张图中的两个包围盒

            WheelColliders的子物体就是四个车轮碰撞器！

            Wheels的子物体就是四个车轮！

    第三部份，代码注解：

           代码使用JS写的！

           首先是：PlayerCar_Script.js

           

// ----------- CAR TUTORIAL SAMPLE PROJECT, ? Andrew Gotow 2009 -----------------

// Here's the basic car script described in my tutorial at www.gotow.net/andrew/blog.
// A Complete explaination of how this script works can be found at the link above, along
// with detailed instructions on how to write one of your own, and tips on what values to 
// assign to the script variables for it to work well for your application.

// Contact me at Maxwelldoggums@Gmail.com for more information.
//这些是外国人写的赛车例子，我个人认为非常好，是用JS写的！
//我来注解一下！
// These variables allow the script to power the wheels of the car.
//前左轮和前右轮
var FrontLeftWheel : WheelCollider;
var FrontRightWheel : WheelCollider;
// These variables are for the gears, the array is the list of ratios. The script
// uses the defined gear ratios to determine how much torque to apply to the wheels.
//齿轮转数系数
var GearRatio : float[];
//档位
var CurrentGear : int = 0;
// These variables are just for applying torque to the wheels and shifting gears.
// using the defined Max and Min Engine RPM, the script can determine what gear the
// car needs to be in.
//向前的动力
var EngineTorque : float = 600.0;
//引擎最大的转速
var MaxEngineRPM : float = 3000.0;
//引擎最小的转速
var MinEngineRPM : float = 1000.0;
private var EngineRPM : float = 0.0;
function Start () {
    // I usually alter the center of mass to make the car more stable. I'ts less likely to flip this way.
    //设置车的中心点，一般在车的底盘下，这样车行驶起来稳定，不会轻易翻车！
    rigidbody.centerOfMass.y = -1.5;
}
function Update () {
    // This is to limith the maximum speed of the car, adjusting the drag probably isn't the best way of doing it,
    // but it's easy, and it doesn't interfere with the physics processing.
    //设置车的阻力为 车的向前的速度的长度除以250
    rigidbody.drag = rigidbody.velocity.magnitude / 250;
    // Compute the engine RPM based on the average RPM of the two wheels, then call the shift gear function
    //档位的转速值车
    EngineRPM = (FrontLeftWheel.rpm + FrontRightWheel.rpm)/2 * GearRatio[CurrentGear];
    ShiftGears();
    // set the audio pitch to the percentage of RPM to the maximum RPM plus one, this makes the sound play
    // up to twice it's pitch, where it will suddenly drop when it switches gears.
    //音频源的音调 发动机的引擎转速越快，则音调越高！
    audio.pitch = Mathf.Abs(EngineRPM / MaxEngineRPM) + 1.0 ;
    // this line is just to ensure that the pitch does not reach a value higher than is desired.
    //超过2.0则归位到2.0
    if ( audio.pitch > 2.0 ) {
        audio.pitch = 2.0;
    }
    // finally, apply the values to the wheels.    The torque applied is divided by the current gear, and
    // multiplied by the user input variable.
    //前面的两个轮子的力矩
    FrontLeftWheel.motorTorque = EngineTorque / GearRatio[CurrentGear] * Input.GetAxis("Vertical");
    FrontRightWheel.motorTorque = EngineTorque / GearRatio[CurrentGear] * Input.GetAxis("Vertical");    
    Debug.Log(Input.GetAxis("Vertical"));
    // the steer angle is an arbitrary value multiplied by the user input.
    FrontLeftWheel.steerAngle = 10 * Input.GetAxis("Horizontal");
    FrontRightWheel.steerAngle = 10 * Input.GetAxis("Horizontal");
}
//换档位
function ShiftGears() {
    // this funciton shifts the gears of the vehcile, it loops through all the gears, checking which will make
    // the engine RPM fall within the desired range. The gear is then set to this "appropriate" value.
    //如果当前引擎的值大于最大引擎
    if ( EngineRPM >= MaxEngineRPM ) {
        var AppropriateGear : int = CurrentGear;
        //则从0开始，往上查，如果左轮的rpm乘以齿轮数小于
        for ( var i = 0; i < GearRatio.length; i ++ ) {
            if ( FrontLeftWheel.rpm * GearRatio[i] < MaxEngineRPM ) {
                AppropriateGear = i;
                break;
            }
        }
        
        CurrentGear = AppropriateGear;
    }
    
    if ( EngineRPM <= MinEngineRPM ) {
        AppropriateGear = CurrentGear;
        
        for ( var j = GearRatio.length-1; j >= 0; j -- ) {
            if ( FrontLeftWheel.rpm * GearRatio[j] > MinEngineRPM ) {
                AppropriateGear = j;
                break;
            }
        }
        
        CurrentGear = AppropriateGear;
    }
}

   解释：

   FrontLeftWheel.motorTorque = EngineTorque / GearRatio[CurrentGear] * Input.GetAxis("Vertical");

   FrontRightWheel.motorTorque = EngineTorque / GearRatio[CurrentGear] * Input.GetAxis("Vertical"); 

   设置车轮的motorTorque可以使车轮滚动！

   FrontLeftWheel.steerAngle = 10 * Input.GetAxis("Horizontal");
   FrontRightWheel.steerAngle = 10 * Input.GetAxis("Horizontal");

   设置车轮的steerAngle可以控制车轮围绕自身Y轴的转向角度！这里的旋转角度是-10度到10度之间！

   作者疑问：

   第57,58,60,61行代码，

   FrontLeftWheel.motorTorque = EngineTorque / GearRatio[CurrentGear] * Input.GetAxis("Vertical");

   Input.GetAxis("Vertical")会返回-1，也就是说motorTorque是负值！

    但是官方文档却说，

    在轮轴上的电机力矩。根据方向正或负。

    To simulate brakes, do not use negative motor torque - use brakeTorque instead.

    模拟刹车，不要使用电机力矩负值，使用brakeTorque代替。

    这两种说法之间可有冲突，请高手指点！

    下篇是车轮与其他物体的碰撞，待续……！