unity 3d example rotation clamp script c#

using UnityEngine;
using System.Collections;

public class RotateClamp : MonoBehaviour {

    Quaternion originalRotation;
    public float rotationLimit = 15;

    // Use this for initialization
    void Start () {
        originalRotation = rigidbody.rotation;
    }

    // Update is called once per frame
    void FixedUpdate () {

        rigidbody.AddRelativeTorque( Input.GetAxis("Vertical") * Vector3.right * 10 );
        rigidbody.AddRelativeTorque( Input.GetAxis("Horizontal") * Vector3.up * 10 );

        if (Vector3.Angle(rigidbody.rotation * Vector3.up , Vector3.up) > rotationLimit)
        {
            Vector3 flatForwardVector = new Vector3( transform.forward.x, 0, transform.forward.z );
            Quaternion flatRotation = Quaternion.LookRotation( flatForwardVector );
            rigidbody.rotation = Quaternion.RotateTowards(flatRotation, rigidbody.rotation, rotationLimit);
        }

    }
}