Unity车辆控制：如何实现未加速时自动减速？

问题 #

希望车辆在不加速时自动减速，现有Unity车辆控制代码如下：

using UnityEngine;  

public class CarWheelControls : MonoBehaviour {
    [SerializeField] WheelCollider frontRight;
    [SerializeField] WheelCollider frontLeft;
    [SerializeField] WheelCollider BackRight;
    [SerializeField] WheelCollider BackLeft;
    [SerializeField] Transform frontRightTransform;
    [SerializeField] Transform frontLeftTransform;
    [SerializeField] Transform backRightTransform;
    [SerializeField] Transform backLeftTransform;

    public float accerelation = 500f;
    public float breakingForce = 300f;
    public float maxTurnAngle = 15f;

    private float currentAccerelation = 0f;
    private float currentBreakForce = 0f;
    private float currentTurnAngle = 0f;

    private void FixedUpdate(){
        //Forward/Reverse acceleration
        currentAccerelation = accerelation * Input.GetAxis("Vertical");

        //pressing "space" gives currentBreakingForce a value
        if (Input.GetKey(KeyCode.Space))
            currentBreakForce = breakingForce;
        else
            currentBreakForce = 0f;

        // Apply accerelation on all wheels. Change to front wheel or rear 
        // wheel drive by deleting fronts or rears :)
        frontRight.motorTorque = currentAccerelation;
        frontLeft.motorTorque = currentAccerelation;
        BackRight.motorTorque = currentAccerelation;
        BackLeft.motorTorque = currentAccerelation;

        //Wheel stopping
        frontRight.brakeTorque = currentBreakForce;
        frontRight.brakeTorque = currentBreakForce;
        BackRight.brakeTorque = currentBreakForce;
        BackLeft.brakeTorque = currentBreakForce;

        //Steering
        currentTurnAngle = maxTurnAngle * Input.GetAxis("Horizontal");
        frontLeft.steerAngle = currentTurnAngle;
        frontRight.steerAngle = currentTurnAngle;

        //Wheel turning
        UpdateWheel(frontLeft, frontLeftTransform);
        UpdateWheel(frontRight, frontRightTransform);
        UpdateWheel(BackLeft, backLeftTransform);
        UpdateWheel(BackRight, backRightTransform);
    
    }

    void UpdateWheel(WheelCollider col, Transform trans){
        //Wheel collider state
        Vector3 position;
        Quaternion rotation;
        col.GetWorldPose(out position, out rotation);

        //Set wheel angle
        trans.position = position;
        trans.rotation = rotation;

    }
}

解决方案 #

要实现不加速时自动减速，只需修改刹车力的逻辑：当没有加速输入（即Vertical轴输入为0）时，给车轮施加一个较小的制动力；同时保留原有的空格急刹功能。具体步骤如下：

1. 添加一个公共变量，用于控制自动减速的力度：

public float slowDownForce = 100f; // 可在Inspector中调整合适的数值

2. 修改FixedUpdate中的刹车力判断逻辑，替换原有的空格判断代码：

// 自动减速+急刹逻辑
float verticalInput = Input.GetAxis("Vertical");
if (Input.GetKey(KeyCode.Space))
{
    currentBreakForce = breakingForce;
}
else if (Mathf.Abs(verticalInput) < 0.01f) // 无加速输入时自动减速
{
    currentBreakForce = slowDownForce;
}
else
{
    currentBreakForce = 0f;
}

3. 修复原代码中的笔误：原代码中frontRight.brakeTorque重复赋值，漏掉了frontLeft的设置，应改为：

//Wheel stopping
frontRight.brakeTorque = currentBreakForce;
frontLeft.brakeTorque = currentBreakForce; // 补上这一行
BackRight.brakeTorque = currentBreakForce;
BackLeft.brakeTorque = currentBreakForce;

修改后的完整代码 #

using UnityEngine;  

public class CarWheelControls : MonoBehaviour {
    [SerializeField] WheelCollider frontRight;
    [SerializeField] WheelCollider frontLeft;
    [SerializeField] WheelCollider BackRight;
    [SerializeField] WheelCollider BackLeft;
    [SerializeField] Transform frontRightTransform;
    [SerializeField] Transform frontLeftTransform;
    [SerializeField] Transform backRightTransform;
    [SerializeField] Transform backLeftTransform;

    public float accerelation = 500f;
    public float breakingForce = 300f;
    public float maxTurnAngle = 15f;
    public float slowDownForce = 100f; // 新增：自动减速力度

    private float currentAccerelation = 0f;
    private float currentBreakForce = 0f;
    private float currentTurnAngle = 0f;

    private void FixedUpdate(){
        float verticalInput = Input.GetAxis("Vertical");
        //Forward/Reverse acceleration
        currentAccerelation = accerelation * verticalInput;

        // 自动减速+急刹逻辑
        if (Input.GetKey(KeyCode.Space))
        {
            currentBreakForce = breakingForce;
        }
        else if (Mathf.Abs(verticalInput) < 0.01f) // 无加速输入时自动减速
        {
            currentBreakForce = slowDownForce;
        }
        else
        {
            currentBreakForce = 0f;
        }

        // Apply accerelation on all wheels. Change to front wheel or rear 
        // wheel drive by deleting fronts or rears :)
        frontRight.motorTorque = currentAccerelation;
        frontLeft.motorTorque = currentAccerelation;
        BackRight.motorTorque = currentAccerelation;
        BackLeft.motorTorque = currentAccerelation;

        //Wheel stopping
        frontRight.brakeTorque = currentBreakForce;
        frontLeft.brakeTorque = currentBreakForce; // 修复笔误
        BackRight.brakeTorque = currentBreakForce;
        BackLeft.brakeTorque = currentBreakForce;

        //Steering
        currentTurnAngle = maxTurnAngle * Input.GetAxis("Horizontal");
        frontLeft.steerAngle = currentTurnAngle;
        frontRight.steerAngle = currentTurnAngle;

        //Wheel turning
        UpdateWheel(frontLeft, frontLeftTransform);
        UpdateWheel(frontRight, frontRightTransform);
        UpdateWheel(BackLeft, backLeftTransform);
        UpdateWheel(BackRight, backRightTransform);
    
    }

    void UpdateWheel(WheelCollider col, Transform trans){
        //Wheel collider state
        Vector3 position;
        Quaternion rotation;
        col.GetWorldPose(out position, out rotation);

        //Set wheel angle
        trans.position = position;
        trans.rotation = rotation;

    }
}

说明 #

• slowDownForce的数值可以在Unity Inspector面板中调整，根据车辆重量和手感设置合适的力度，数值越大减速越快。
• 使用Mathf.Abs(verticalInput) < 0.01f判断是为了避免输入轴的微小波动导致误触发自动减速。

内容的提问来源于stack exchange，提问作者Ju_hb