Importing CAD model on isaac sim

Hi, I imported a CAD(.step) file of a small custom RC car of a robotics company on Isaac sim. There is so many individual pieces on the model. Since it’s just a mesh and it has no joints or physics, I know it wouldn’t move. I want its wheels to rotate. I went through the tutorial. I tried to group all the parts except the wheels so that it acts like 2 bodies. I cant group them. It shows an error. Then i made individual pieces rigid body . But then everything falls apart on starting simulation. I was wondering how i can make other parts stick together. Theres 200 pieces. do i have to make joints for every single of them. I don’t think thats feasible. Is there anyway to group items together so that they move together. When i make the whole car rigid, it does move together and doesn’t fall apart. but i cant make the wheels rotate

I cant add revolute joints. I get an error. because the wheels and the rim weren’t rigid bodies. I can’t make the whole model rigid. it has to be the individual pieces

You should learn Onshape, once you are familiar with Onshape, importing robots should be easy. Import CAD models to Isaac Sim has one disadvantage, that is you have to rig the robot your self, and Isaac Sim has no snapping tool for that job, but Onshape does.