You can export meshes from Blender either as DAE or OBJ files and use them in Gazebo. Here's a tutorial on importing meshes. If you want the meshes to move with respect to each other, you should put each mesh in a different link. This tutorial has some information about the different parts of a model in Gazebo.

Once you got your model working in Gazebo, you can control it with ROS as explained on this tutorial.