charactor controller角色做平衡木的问题，和小球走平衡木不一样，charctor controller是不可以对地面产生压力的，无论角色是否加了刚体，charactor controller都只具有自由下落，而不具有对地面压力。如果换成box collider等碰撞检测，上下楼梯角色运动的时候很容易倒下。针对这个问题，做出了以下解决方案：

var speed = 10.0;

var gravity = 10.0;

var maxVelocityChange = 10.0;

var canJump = true;

var jumpHeight = 2.0;

private var grounded = false;

@script RequireComponent(Rigidbody, CapsuleCollider)

function Awake ()

{

    rigidbody.freezeRotation = true;

    rigidbody.useGravity = false;

}

function FixedUpdate ()

{

    if (grounded)

        // Calculate how fast we should be moving

        var targetVelocity = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));

        targetVelocity = transform.TransformDirection(targetVelocity);

        targetVelocity *= speed;

        // Apply a force that attempts to reach our target velocity

        var velocity = rigidbody.velocity;

        var velocityChange = (targetVelocity - velocity);

        velocityChange.x = Mathf.Clamp(velocityChange.x, -maxVelocityChange, maxVelocityChange);

        velocityChange.z = Mathf.Clamp(velocityChange.z, -maxVelocityChange, maxVelocityChange);

        velocityChange.y = 0;

        rigidbody.AddForce(velocityChange, ForceMode.VelocityChange);

        // Jump

        if (canJump && Input.GetButton("Jump"))

        {

            rigidbody.velocity = Vector3(velocity.x, CalculateJumpVerticalSpeed(), velocity.z);

        }

    }

    // We apply gravity manually for more tuning control

    rigidbody.AddForce(Vector3 (0, -gravity * rigidbody.mass, 0));

    grounded = false;

}

function OnCollisionStay ()

{

    grounded = true;   

}

function CalculateJumpVerticalSpeed ()

{

    // From the jump height and gravity we deduce the upwards speed

    // for the character to reach at the apex.

    return Mathf.Sqrt(2 * jumpHeight * gravity);

}