Rigidbody sleeping prevents collision detection

Questions & Answers
1

Hello, I’m trying to detect the collision between two game objects. The first object is a static sphere collider with a rigidbody attached, on a user defined layer and no gravity enabled.

The second object is a user controlled sphere collider (parented) with no rigidbody attached and on the same user defined layer as the static collider.

I think because the first static game object doesn’t move, its rigidbody goes to sleep and stops detecting collision with the player.

And so I’ve added a rigidbody to the player on the parented sphere collider. But I think because the rigidbody is parented to the player and I use a character controller to move the player, that rigidbody is also considered nonmoving and also goes to sleep.

How am I supposed to detect collisions now? Is there a certain best practice to follow when creating my player prefabs in terms of components and parenting?

2

You may have already read through this page, but it explains all the combinations that work: Unity - Manual: Introduction to rigid body physics (Was: http://docs.unity3d.com/Documentation/Components/RigidbodySleeping.html)

If your first object is static and you just want to know when player (second object) enters its bounds, you could remove the first object’s rigidbody and make it a static trigger.

I don’t think the player’s rigidbody child should fall asleep.

Are your layers correct? Double-check Edit > Project Settings > Physics to make sure collisions are enabled.

To get verification that sleeping is the real problem, you could add a temporary test script to keep the rigidbodies awake. Something like:

void Update() {
    if ((rigidbody != null) && rigidbody.IsSleeping()) {
        rigidbody.WakeUp();
    }
}

If they still fail to register collisions, then it’s not a sleep problem.

3

I know this is an old thread, but I had a similar problem, and to fix it I did the following:
On the rigidbody I set

  • collision detection to continuous
  • sleeping mode to never sleep

and it seemed to work for me.

4

You can set Rigidbody.sleepThreshold to 0 to disable rigidbody sleeping feature.

    m_Rigidbody = GetComponent<Rigidbody>();
    m_Rigidbody.sleepThreshold = 0.0f;
5

You can use

void Start()
{
this.GetComponent<Rigidbody>().sleepThreshold = 0.0f;
}

this worked for me