How do i make an objact without waight and mass-point effekt

[Drachenbauer]

Hello

I´m creating Angry-Birds-marbles for marble-race-simulations.

I use common marbles, provided by another user and add Angry-Birds-sprites as a third objrct ontop.
I make the original circle invisible and the rectangle with the sprite-graphic in no collision-group, to still have the circle for the collison-effects.
I do it this way, because i want the body-size (without head- and tail-feathers) match the size of the circle from the marble.
If the whole bird-sprite fit´s inside the circle, it looks too small.

Algodoo Marbles.png

(35.65 KiB) Not downloaded yet

Already turned a marble inte a sprite from Stella from the angry birds, the others wait to be modifyed

But now i have a question:
actueaay the mass-point of the modifyed marble is not exactly in it´s center.
So on a horizontal surface, it acts similar to a standup figure (oscillates to the left and right, until it finds it´s balance with the mass-point down).
How can i remove the wight and mass-center-effects of the rectangle with the bird-sprite from the marble to make it act exactly like it did without the sprite?

I want to change the look of the marbles, but not their physics
They should be still compatible to the marble-race track-parts from the user, i got the marbles from.

Edit: i found a solution:
i set the density value of the aditional bird-sprite-part to 0,0100.
It seems, this is the density of the air in this simulation.
so the marble get´s its physics now only from it´s now invisible circle-part.

[Ken3344]

Yeah, that works, you can also make it a photo.