Joints and Motors - Box2D for Flash Games - page 104

dJoint.localAnchorB=new b2Vec2(0,0);
dJoint.length=100/worldScale;
var distanceJoint:b2DistanceJoint;
distanceJoint=world.CreateJoint(dJoint) as b2DistanceJoint;
addEventListener(Event.ENTER_FRAME,updateWorld);
}

13. And there's nothing new at the moment, but you were able to start building
your siege machine anyway. Test the movie:

Your carts now have wheels and are linked by a distance joint. Now we must
introduce something new to allow players to move the truck.

Controlling joints with motors
Some joints, such as the revolute joint feature motors, which in this case can be used
to rotate the joint at a given speed unless a given maximum torque is exceeded.

Learning motors will allow you to develop every kind of car/truck game you see on
the Web.

1. To create the truck, we need to apply a motor on the rightmost cart, so in the

addCart function we are adding an argument to tell us whether it should
have a motor or not. Change the Main function to specify that frontCart
will have a motor while rearCart won't:
public function Main() {
world=new b2World(new b2Vec2(0,5),true);
debugDraw();
ground();
var frontCart:b2Body=addCart(200,430,true);
var rearCart:b2Body=addCart(100,430,false);