Making an NPC/Mech model

I’m wondering how you would actually rig/weld the model together if it doesn’t have any base parts that an r6 model does (aka, the left arm instead being a model made of motor6d connected parts). Would it be animatable? I’ve tried making models/NPCs like this before, but they either made rig edit plugin really hard to use, or just straight up continued to fall apart.
Also am I in the right category?