Stopping 3D object in place

Question

I am at 1.2 stage (moving the player) at Unity course "Roll-a-ball" and have question:

I want to add feature that stops a player and sets his new position on 0, 0, 0.

I can reset the position, but I have really problem with stopping a player. The ball won't stop rolling.

My code is:

    using UnityEngine;
    using System.Collections;

    public class PlayerController : MonoBehaviour {

        private Rigidbody rb;
        public float speed = 1.0f;

        void Start()
        {
            rb = GetComponent<Rigidbody>();
        }

        void FixedUpdate()
        {
            float moveHorizontal = Input.GetAxis("Horizontal");
            float moveVertical = Input.GetAxis("Vertical");

            Vector3 movement = new Vector3(moveHorizontal, 0.0f, moveVertical);

            rb.AddForce(movement*speed);
            if (Input.GetKeyDown(KeyCode.Space))
            {
                rb.position = new Vector3(0,0.5f,0);
            }
            print(movement);
        }
    }

What I tried?

• Adding new vector3 (0,0,0) in if section,
• New vector3 that is opposite to movement,
• .Stop after ascribing new position to (0,0,0), but it 'freezes' before (example: I click space when sphere is at board's edge, then it freezes there, when I click arrow it go to new position and start going).

So, how to do that? I have no clue right now, although problem seems be easy.

Here a image with code and Unity with opened Inspector on object.

EDIT

I've a another problem.

Changed code as below (as Byte56 suggested):

if (Input.GetKeyDown(KeyCode.Space))
{
    speed = 0;
    rb.velocity = Vector3.zero;
    rb.transform.position = new Vector3(0, 0.5f, 0);
    rb.constraints = RigidbodyConstraints.FreezeAll;
    speed = 1.0f;
}
if (moveHorizontal != 0 || moveVertical != 0)
{
    rb.constraints = RigidbodyConstraints.None;
}

It seems like clicing space not always freezes object. It always put it on right place, but sometimes doesn't freeze. No matter if I use code rb.constraints = RigidbodyConstraints.FreezeAll; or rb.Sleep(); - sometimes it works, sometimes not. I can't prove it, but it seems the smaller is delta of time between clicking space (smaller than 1 second) the chance that it won't freeze increases. It's not fault of space, I tried it with NumEnter. Any idea? It seems really buggy.

Answer 1

If you want to stop a physics object from moving, you need to zero the forces and the velocity of the RigidBody.

rb.velocity = new Vector3(0,0,0);

For zeroing the force, you can apply a force opposite to the forces you've added that frame already. However, I'd suggest simply not adding those forces if you're stopping. It means a slight rearrangement of your code.

if (Input.GetKeyDown(KeyCode.Space))
{
    rb.position = new Vector3(0,0.5f,0);
    rb.velocity = new Vector3(0,0,0);
} else {
    rb.AddForce(movement*speed);
}

The ultimate way to stop the ball, activating all the constraints on the rigidbody.

if(moveHorizontal != 0 || moveVertical != 0) //for starting the movement again
    rb.constraints = RigidbodyConstraints.None;

if (Input.GetKeyDown(KeyCode.Space))
{
    rb.gameObject.transform.position = new Vector3(0,0.5f,0);
    rb.constraints = RigidbodyConstraints.FreezeAll;
} else {
    rb.AddForce(movement*speed);
}

Answer 2

It is due to constantly applying AddForce in FixedUpdate. You can easily do it by assigning zero to speed and set velocity to zero.

rb.AddForce(movement*speed);
        if (Input.GetKeyDown(KeyCode.Space))
        {
            speed = 0;
            rb.AddForce(-rb.velocity);
            rb.velocity = Vector3.zero;
            rb.position = new Vector3(0,0.5f,0);
        }

// Change speed from zero to any other value when you want to move it again.