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);
     var dJoint:b2DistanceJointDef=new b2DistanceJointDef();
     dJoint.bodyA=frontCart;
     dJoint.bodyB=rearCart;
     dJoint.localAnchorA=new b2Vec2(0,0);
     dJoint.localAnchorB=new b2Vec2(0,0);
     dJoint.length=100/worldScale;
     var distanceJoint:b2DistanceJoint;
     distanceJoint...