Sprites not recognized as whole-spinning in different directions

Hi,

While developing my game (unity newbie) I stumbled upon a problem..

Game is in 2D and in C#.

I have a wheel composed from smaller wheels (like gears on main wheel). Between them there is some empty space (sprite is added as one png).

Object has Sprinte Renderer(for displaying image), Rigidbody 2D, and Circle colider 2D added.

When adding force to wheel (going downhill) sprite start behaving strange. At first they all spin in the same-right direction, but in a few moments the inner wheel starts rotating in different.. Everything starts spinning in different directions-its like unity slices png and every layer behaves on its own.

Could anyone help me?

Thanks