What is the methodology used at robot companies to design and develop a new robot?

Hello,

My background is a MS in control theory, and I currently work as a software engineer in a team which consists of mechanical and electrical engineers. We don't have any prior experience designing a 6 dof robot arm, but we've been tasked with this project to attempt a custom robot design for a niche application.

From what I understand, the big industrial robot companies (Kuka, Fanuc, ABB, etc.) have large teams of engineers (controls, mech, elec, software, etc) working for many years on a design to bring it to a product-ready state. How correct is this?

Can someone who works/has worked at one of the big robot companies please elaborate on the methodology used?

We are using off-the-shelf components like PLC, motors, drives, etc. How easy or difficult is it to design a robot arm from scratch?