Using Unity Physics to consistently bounce a ball to the same height

Question

My ball can only bounce on the y axis. X and Z movement as well as all rotation are locked in the rigidbody component. Originally I was planning to handle this using a combination of the two methods below. I'm adding my own faux-gravity to the object in FixedUpdate and bouncing the ball upwards when it collides with a platform in OnCollisionEnter. Esentially sending it bouncing up and down forever.

void OnCollisionEnter(Collision collision)
{
    ball.AddForce(Vector3.up * force, ForceMode.Impulse);
}

void FixedUpdate()
{
    Vector3 gravity = globalGravity * Vector3.up;
    ball.AddForce(gravity, ForceMode.Acceleration);
}

The problem is that if I place an angled platform under the ball, it no longer bounces vertically with the same force. I believe this is because Unity Physics is calculating the angle/force the object should bounce in a 3D space, and then because of my script only applying the upward force of that calculation. However, I'd like my ball to bounce with a consistent vertical force regardless of the angle of the platform placed under it.

This could be achieved using a coroutine and Lerp to a certain height, which I tried using the script below, using Physics gravity this time, but it didn't have the same natural bouncing feel as Unity Physics. I'd like to go back to using the Physics system but I don't know how to stop Unity from doing the angular calculation and just launch my ball vertically with the force I want.

IEnumerator MoveBall(Vector2 newPos, float time)
{
    ball.useGravity = false;
    float elapsedTime = 0;
    Vector2 startingPos = transform.position;
    while (elapsedTime < time)
    {
        transform.position = Vector2.Lerp(startingPos, newPos, (elapsedTime / time));
        elapsedTime += Time.deltaTime;
        yield return null;
    }
    ball.useGravity = true;
}

Foggzie Foggzie · Accepted Answer · 2019-04-15T22:48:06

It sounds like you want your collider to be setup as a trigger. On your ball's collider, set isTrigger to true and then use OnTriggerEnter instead of OnCollisionEnter. This will prevent Unity's physics engine from creating and resolving a Collision between the ball and whatever it hits.

If you'd also want the ball to bounce off other objects in way that uses Unity's Physics, you'll need to then get creative with which colliders are/arent' triggers, and which physics layers they belong to.

Using Unity Physics to consistently bounce a ball to the same height

1 Answers