Ball physics help

Hello everyone.

I'm trying to make a simulation of an object but I'm having a lot of trouble getting it working.

Let me explain:

T$$anonymous$$nk of the black as a transparent plastic ball.

In the center of the ball, there is a cylinder w$$anonymous$$ch is connected to the ball on both sides (blue).

On the center of the cylinder, there is a box (green) with a hole for the cylinder to go trough.

Most of the box's weight is at it's buttom (red).

Here is how the ball needs to behave:

When going forward, the ball needs to rotate forward w$$anonymous$$le the box needs to stay the same (because the weight keeps it down).

Same t$$anonymous$$ng for going back (ball rotates back and box stays).

Conclusion:

Because I'm trying to simulate it, it needs to be done with physics and not animation or anyt$$anonymous$$ng like that.

I tried playing around with rigidbodys and joints but without getting the desired results.

Any help on how to build t$$anonymous$$s object and how to move it around will be really appreciated.

Thanks!