How to create an entity that can pick up blocks

Kind of a noob question I think. So I’m simulating robots, but the problem I have is that I have no idea how to make collisions between one part of the 3D model connect to cubes for example and then wherever the arm goes, the cube goes. It can’t be with the whole 3D model, it has to be a specific portion, which I would also appreciate explanation in how to do that. I’m currently trying to get the 3D model, and if I don’t forget about this I’ll post the GitHub to it

Moving this up