零重力box2d世界中的遞減速度

我正在試圖創建一個動態的物體，它圍繞Box2D中的一個靜態物體進行軌道運動。我有一個零重力世界，和一個連接兩個身體的DistanceJoint。我已經消除了身體和關節的所有摩擦和阻尼，並且正在向動體施加初始線速度。其結果是人體開始繞軌道運行，但隨着時間的推移，其速度逐漸減小 - 這在沒有摩擦的零重力環境中我並不期待。零重力box2d世界中的遞減速度

我做錯了什麼？線性速度應該在每一步重新創建，還是我可以將這項工作委託給Box2D？

下面是相關代碼：

// positions of both bodies 

Vector2 planetPosition = new Vector2(x1/Physics.RATIO, y1/Physics.RATIO); 
Vector2 satellitePosition = new Vector2(x2/Physics.RATIO, y2/Physics.RATIO); 


// creating static body 

BodyDef planetBodyDef = new BodyDef(); 
planetBodyDef.type = BodyType.StaticBody; 
planetBodyDef.position.set(planetPosition); 
planetBodyDef.angularDamping = 0; 
planetBodyDef.linearDamping = 0; 

planetBody = _world.createBody(planetBodyDef); 

CircleShape planetShapeDef = new CircleShape(); 
planetShapeDef.setRadius(40); 

FixtureDef planetFixtureDef = new FixtureDef(); 
planetFixtureDef.shape = planetShapeDef; 
planetFixtureDef.density = 0.7f; 
planetFixtureDef.friction = 0; 

planetBody.createFixture(planetFixtureDef); 

// creating dynamic body 

BodyDef satelliteBodyDef = new BodyDef(); 
satelliteBodyDef.type = BodyType.DynamicBody; 
satelliteBodyDef.position.set(satellitePosition); 
satelliteBodyDef.linearDamping = 0; 
satelliteBodyDef.angularDamping = 0; 

satelliteBody = _world.createBody(satelliteBodyDef); 

CircleShape satelliteShapeDef = new CircleShape(); 
satelliteShapeDef.setRadius(10); 

FixtureDef satelliteFixtureDef = new FixtureDef(); 
satelliteFixtureDef.shape = satelliteShapeDef; 
satelliteFixtureDef.density = 0.7f; 
satelliteFixtureDef.friction = 0; 

satelliteBody.createFixture(satelliteFixtureDef); 

// create DistanceJoint between bodies 

DistanceJointDef jointDef = new DistanceJointDef();   
jointDef.initialize(satelliteBody, planetBody, satellitePosition, planetPosition); 
jointDef.collideConnected = false; 
jointDef.dampingRatio = 0; 

_world.createJoint(jointDef); 

// set initial velocity 

satelliteBody.setLinearVelocity(new Vector2(0, 30.0f)); // orthogonal to the joint

來源

2010-07-30 Alex Gyoshev