调用private var到便利init（swift）

Im trying to create a node class of a ball. the ball supposed to have some physics body properties - because of that i created a function that init the physicsbody properties. also, I want that the user will set up the ball radius (via circleOfRadius) which I set up via convenience init. because of that I set the radius var as a private. the problem is the I can set the radius to there private var but then the convenience is not executed. here is my code:Im trying to create a node class of a ball. the