AddForce has no effect on my cannonball.

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Hey folks, first post so if something is wrong please let me know?

I am creating an augmented reality game with two cannons shooting at each other, I have a script attached to the barrel of my cannon to instantiate a cannonball to be fired, when a button on the mobile device is pressed.

My problem is that the cannonball appears and simply falls to the ground under the force of gravity, I can fire(spawn) lots and they react with one another but there is no movement in any direction other than the vertical axis.

My code is as follows

var cannonBallPrefab : Transform;

function Update () { if(Input.GetKeyDown(KeyCode.Menu)) { var cannonBall = Instantiate(cannonBallPrefab, transform.position, Quaternion.identity) as GameObject;

     cannonBall.rigidbody.AddForce(Vector3.right * 40000);
 }

}

I have read other peoples attempts to solve this problem but none seem to work, it is rigidbody, not kinematic, I have tried excessively large and small forces, large and small masses, there are no mesh colliders other than that of the cannonball itself.

I really dont know what to do

any help would be amazing

Thanks in advance

Euan Hislop

Answer 1

Best Answer

Answer by Chris D · Mar 03, 2011 at 10:44 PM

I've had luck with my code below. It's got a few extra items in there, but successfully spawns at the cannonballSpawn transform and applies force to the instanced ball, relative to the spawn's position and rotation.

var cannonballSpawn : Transform; var cannonballPrefab : GameObject; var cannonForce : int;

function Update() {
    if(Input.GetButtonUp("Fire1")) {
        var projectile = Instantiate(cannonballPrefab,
                                     cannonballSpawn.position,
                                     Quaternion.identity);
        projectile.rigidbody.AddRelativeForce(transform.up* cannonForce);//cannon's axis
    }
}

edit:

on taking a look at our codes, the only real difference I see is straight up Instantiating my prefab as a GameObject as opposed to a transform. Maybe there's something happening there?

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Yons · Mar 03, 2011 at 11:14 PM 0

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Genius! Thank you for the help. I am guessing this line 'var cannonBallPrefab : Transform;' is where the problem was co$$anonymous$$g from, although I looked at tutorials that used it, this works! Thank you so much!

Chris D · Apr 29, 2011 at 05:01 PM 0

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No problem, glad to help. Co$$anonymous$$g back and looking at this now, I think I'm making the mistake of adding force in the Update as opposed to FixedUpdate...oh well.

Answer 2

Answer by tertle · Mar 03, 2011 at 10:19 PM

The default ForceMode of AddForce is ForceMode.Force

ForceMode.Force is intended to be put on an object over various frames.

GetKeyDown will only run for a single frame.

You should look at changing the ForceMode. In this case an Impulse force might work as intended for a realistic cannon effect.

cannonBall.rigidbody.AddForce(Vector3.right* 40000, ForceMode.Impulse);

Note with you applying such a high force, Vector3.right* 40000, your cannon ball is likely to instantly be shot 1000km away.

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Yons · Mar 03, 2011 at 10:28 PM 0

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Wow, thanks for the speedy comment but unfortunately this did not work.

I tried using Force$$anonymous$$ode.Impulse but there was no effect again, when you say

"Force$$anonymous$$ode.Force is intended to be put on an object over various frames."

do you mean kind of like using the 'FixedUpdate()' function, cause I tried this as well to no effect! I maybe should not have posted using such a high value that was just for testing as some other users had solved there problems by using a higher force.

Thanks

Euan Hislop

tertle · Mar 03, 2011 at 10:44 PM 0

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Ideally you should do all rigidbody stuff (adding forces etc) in FixedUpdate. $$anonymous$$ay be a silly question, but does your cannonBallPrefab actually have a rigidbody attached to it? Finally

Yons · Mar 03, 2011 at 10:50 PM 0

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I tried using FixedUpdate, but once again it did not work, and it was creating two cannonballs sometimes. The cannonBallPrefab does have a rigidbody attached to it, I am very confused, I have tried all the solutions that worked for other people lol Thanks Euan Hislop

Answer 3

Answer by efge · Mar 03, 2011 at 10:26 PM

If you only want to access the Rigidbody of the instantiated object you could do this.
Define a Rigidbody and set it's velocity along z-axis:

var cannonBall : Rigidbody =  Instantiate(cannonBallPrefab, transform.position, Quaternion.identity);
cannonBall.velocity = transform.TransformDirection (Vector3.forward * factor);

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Yons · Mar 03, 2011 at 10:42 PM 0

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Hey thanks for the reply

But this also did not work.

I will keep on plugging away though

Thanks

Euan Hislop

AddForce has no effect on my cannonball.

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