Animate a character with individuals parts

So, i’m tryng to make a game where you control a mech and this mech has a member system.

what i mean is that he has 3 different types of members (2 weapons, a base body and mobility) and in my game gonna have a bunch of parts for the player upgrade his mech.

i was wondering on how i’m suppose to merge the conections of thoses parts with the main body like scrap mechanic. i don’t think i explain this well but what i’m trying to know is how to connect individuals parts in the main body and make it look like a single character.