Unity Instantiated object only moves up

Question

I have a Light_Spell script attached to a magic wand which is parented to a Razer Hydra hand object. The Light_Spell takes a prefab of a Light which is projected out of it when a button is pressed. However the light is just moving up, no matter what way I rotate the hand object, it always goes up. I had it working but I changed some code around and can't remember how I got it working in the first place.

Here is the code I have so far:

    //What happens when bumper is pressed
    if (isSelectedSpell && SixenseInput.Controllers [0].GetButtonDown (SixenseButtons.BUMPER) && triggerIsPressed == false) {
        Rigidbody instantiateProjectile = Instantiate(projectile, transform.position, transform.rotation) as Rigidbody;
        instantiateProjectile.position += Vector3.down * 20.0F;
    }

I have tried setting Vector3 to up and forward and a whole set of different things. Any ideas on what I should do to make it match the rotation of where the hand is pointing and stuff? Thanks

Answer 1

Consider using:

instantiateProjectile.position += -instantiateProjectile.transform.up * 20.0f;

Explanation:

Vector3.down is not relative to the transform's rotation, it is a 'down' in World space, that is to say it will always be going down according to the cardinal axes.

transform.up is relative to that transform's rotation. If the projectile is rotated, the axes used to obtain "up" are rotated too. We must use an inverted transform.up instead of transform.down because no transform.down exists.