Bumper car physics

Unity Engine
1

Hi,

I’m developing a game with a faux car physics, which is actually a box with almost 0 frictions physic material pushed around along its forward vector. I’ve mentioned this in my previous thread (which doesn’t get any reply, unfortunately): Car Tutorial didn't work in Unity 5.0.1 - Unity Engine - Unity Discussions . I can’t use the wheel collider and I didn’t make a raytracing one for the car physics. But the one I use is actually good enough, because my game is only an isometric car game, like “Pako Car Chase” or “Mini Motor Racing”.

Now, I’ve got a physics problem. My employer wanted me to make a physics that will behave unlike the usual physics if colliding into a wall. I don’t know how to put it into English, so I’ll put it into some images.

Currently, the usual physics of collision will go like this, right?

2150005--141895--normal1.png
2150005--141895--normal1.png1152×720 2.33 KB
2150005--141896--normal2.png
2150005--141896--normal2.png1152×720 1.75 KB

But, my employer wanted it to go like this:

2150005--141895--normal1.png
2150005--141895--normal1.png1152×720 2.33 KB

2150005--141897--abnormal2.png
2150005--141897--abnormal2.png1152×720 1.03 KB

So basically, maybe he wanted it to behave similarly to a bumper car. If the car collided with a wall, it won’t bounce but will traverse along the wall instead. So, any idea about how to do that? I’m currently blank right now. Thanks.

2

Maybe this can be a starting point.
Note - I have not tested this to much.
Click for code

using UnityEngine;

public class ConvertBounce : MonoBehaviour
{
    Rigidbody myRigidbody;
    Vector3 velocityBeforeCollision;

    void Start()
    {
        myRigidbody = gameObject.GetComponent<Rigidbody>();
        myRigidbody.constraints = RigidbodyConstraints.FreezeRotation;
    }

    void FixedUpdate()
    {
        velocityBeforeCollision = myRigidbody.velocity;
    }

    void OnCollisionEnter(Collision collisionInfo)
    {
        if(collisionInfo.collider.tag == "Wall")
        {
            Vector3 normal = Vector3.zero;
            foreach(ContactPoint contact in collisionInfo.contacts)
            {
                normal += contact.normal;
            }
            normal.Normalize();
            Vector3 newDirection = Vector3.Cross(normal, Vector3.Cross((velocityBeforeCollision), normal));
            newDirection.Normalize();

            myRigidbody.velocity = newDirection * velocityBeforeCollision.magnitude;
            myRigidbody.transform.rotation = Quaternion.LookRotation(newDirection);
        }
    }
}

Place this on your car, Make all walls tags to “Wall”, and it should work.

3

Set up the physic materials of both car and wall so the bounce factor of their collision result 0.

There are several setups that result a bounce factor of 0. The simplest one would be to configure a physic material with bounciness = 0 and bounceCombine = minimum. You should also do the same with both dynamic and static frictions. With frictions, you might want to use small values as well (~0.05 - 0.1) so the car looses some speed when colliding. Assign this physic material to all the colliders in the car.

4

Hi guys, thanks for the replies. I was trying to tweak the physic material the other day, and it is working. Thanks Edy.

@Edy : BTW, can I ask a rather OOT question. As you can see, I was using a faux car physics because wheel collider behaved strangely in my project. My original question of this problem can be found here: Car Tutorial didn't work in Unity 5.0.1 - Unity Engine - Unity Discussions . Now I’ve browsed the forum and answer, and I found out that you are also experiencing a problem with the new Unity 5 wheel collider. Any idea about how to solve it?

Thanks again.