AndEngine rotate all connected bodies

Question

I have created below hexagon structure in Andengine with box2D physics extension. I want to rotate whole structure with respect to center when other ball collides with the structure using physics.

I tried weld joint and revolute joint with the bodies but it is not performing proper motion as required. All bodies are attached with weld joint and vertices have revolute joint with center body which is static like,

RevoluteJointDef revoluteJointDef1 = new RevoluteJointDef();
revoluteJointDef1.initialize(centerB, movingBody[i], centerB.getWorldCenter());
revoluteJointDef1.enableMotor = true;
revoluteJointDef1.motorSpeed = 0;
revoluteJointDef1.maxMotorTorque = 1f;
this.mPhysicsWorld.createJoint(revoluteJointDef1);

I had refered these links: box2d manual and box2d joints tutorial

Is there any other way to perform smooth rotation of whole structure? Thanks.

Answer 1

If the circles never need to move independently, you can make one body. See here for an example of a hexagon body. I've extracted the relavent bits and pasted them here:

import static org.anddev.andengine.extension.physics.box2d.util.constants.PhysicsConstants.PIXEL_TO_METER_RATIO_DEFAULT;
import com.badlogic.gdx.math.Vector2;
import com.badlogic.gdx.physics.box2d.Body;
import com.badlogic.gdx.physics.box2d.BodyDef.BodyType;
import com.badlogic.gdx.physics.box2d.FixtureDef;
import com.badlogic.gdx.physics.box2d.PolygonShape;

/* ... */

public class PhysicsExample extends BaseExample implements IAccelerometerListener, IOnSceneTouchListener {

    /* ... */

    private static Body createHexagonBody(final PhysicsWorld pPhysicsWorld, final Shape pShape, final BodyType pBodyType, final FixtureDef pFixtureDef) {
    /* Remember that the vertices are relative to the center-coordinates of the Shape. */
        final float halfWidth = pShape.getWidthScaled() * 0.5f / PIXEL_TO_METER_RATIO_DEFAULT;
        final float halfHeight = pShape.getHeightScaled() * 0.5f / PIXEL_TO_METER_RATIO_DEFAULT;

    /* The top and bottom vertex of the hexagon are on the bottom and top of hexagon-sprite. */
        final float top = -halfHeight;
        final float bottom = halfHeight;

        final float centerX = 0;

        final float left = -halfWidth + 2.5f / PIXEL_TO_METER_RATIO_DEFAULT;
        final float right = halfWidth - 2.5f / PIXEL_TO_METER_RATIO_DEFAULT;
        final float higher = top + 8.25f / PIXEL_TO_METER_RATIO_DEFAULT;
        final float lower = bottom - 8.25f / PIXEL_TO_METER_RATIO_DEFAULT;

        final Vector2[] vertices = {
            new Vector2(centerX, top),
            new Vector2(right, higher),
            new Vector2(right, lower),
            new Vector2(centerX, bottom),
            new Vector2(left, lower),
            new Vector2(left, higher)
        };

        return PhysicsFactory.createPolygonBody(pPhysicsWorld, pShape, vertices, pBodyType, pFixtureDef);
    }
}

EDIT:

I know the OP has found a working solution to their problem, but I thought I would update my answer anyway. I think the best way is still to make just one body, but you can add multiple fixtures to it (Example done in RUBE):

When a collision happens, the fixture (e.g. ball) in contact is passed to all the collision callbacks, so you don't have to worry about implementing any fancy system to determine which ball was hit in a collision.

IMO this is a lot cleaner and faster than creating new bodies for every ball, and then joining every body to a central one using weld joints.

Answer 2

Oh! i got solution by myself... I did the same thing as i mentioned in first comment my question where I attached balls on a big circle body like,

Body circleBody ... ;// having large radius
//for all balls arranged in hexagon structure
foreach BallBody b
{ 
WeldJointDef def = new WeldJointDef();
def.initialize(b, circleBody, b.getWorldCenter());
mPhysicsWorld.createJoint(def);
}

and got the rotation by having revolute joint of circleBody with center. Thanks who put their efforts.