How to apply force at a specific position on a body

Hi,

I have a space ship, and it needs to have a left, middle and right thruster. I was hoping to simply weld 3 thruster rigid bodies to the space ship and simply apply a force directly to the thrusters, but there is no box2D weld joint.

So I think I need to add 3 child game objects which are not physics objects to the space ship, and apply a force to the main spaceship at these positions. Is this the correct approach, and how do I apply a force at those positions...do I apply a force at a world position, or a local position of the spaceship - if world space, how do I get the position vector i need to apply the force at.

Any help appreciated.

Regards

Stephen

 

http://docs.unity3d.com/Documentation/ScriptReference/Rigidbody2D.AddForceAtPosition.html

It is world space. However, you have the child object (engine) transform and rotation, so you can simply apply the force to the parent (ship) at the current transform position.

 

Hi,

Thanks, it was easier than I thought...transform gives world space anyway, even on child objects so no translation required.

Got in a pickle for an hour, because I forgot to Mathf.Abs the horizontal access value and so it only ever turned one way ;-)


public class LanderScript : MonoBehaviour {

public GameObject leftThruster;
public GameObject rightThruster;
public GameObject mainThruster;
public float thrustForce = 2f;
public float sideThrustForce = 2f;
// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update () {
Camera mainCamera = Camera.main;

float leftRightThrust = Input.GetAxis("Horizontal");
float mainThrust;


if(Input.GetKey("joystick button 16")) {
mainThrust = 1.0f;
} else {
mainThrust = 0f;
}

//Vector3 leftThrustPos = transform.TransformPoint(leftThruster.transform.position);
Vector2 leftThrustPos = new Vector2(leftThruster.transform.position.x, leftThruster.transform.position.y);
Vector2 rightThrustPos = new Vector2(rightThruster.transform.position.x, rightThruster.transform.position.y);
Vector2 mainThrustPos = new Vector2(mainThruster.transform.position.x, mainThruster.transform.position.y);

Debug.Log("leftThrustPos " + leftThrustPos.x + " " + leftThrustPos.y);
Debug.Log("rightThrustPos " + rightThrustPos.x + " " + rightThrustPos.y);
Debug.Log("mainThrustPos " + mainThrustPos.x + " " + mainThrustPos.y);

if(leftRightThrust < -0.2) {
Debug.Log("applying thrust to turn left");

rigidbody2D.AddForceAtPosition(transform.up * Mathf.Abs(leftRightThrust) * sideThrustForce, rightThrustPos);
} else if(leftRightThrust > 0.2) {
Debug.Log("applying thrust to turn right");

rigidbody2D.AddForceAtPosition(transform.up * Mathf.Abs(leftRightThrust) * sideThrustForce, leftThrustPos);
}

if(mainThrust > 0) {
rigidbody2D.AddForceAtPosition(transform.up * thrustForce, mainThrustPos);
}
//leftThruster.AddForce(Vector2.up * thrust);
}
}