Are the humanoids drivers of their engines or are they the engine themselves (transform into the engine) since steam engines have firemen but can consume coal?
The humanoids are the drivers. Some humanoids in my au used to transform into heir engines but those were the original humanoids in my au. Those humanoids are either retired or scrapped. Those humanoids were know to have many problems
Now the humanoids are just humanoids they cannot transform into their engines but they drive it. Though some engines do need a extra driver because some humanoids are known to shut down a lot because they forget to get coal, water, diesel fuel, or there's a problem with that humanoid. Though luckily they only need to eat that stuff once a month or two.
For example Duck: He normally forgets to eat coal, water, or any food and this caused him to get a extra driver who almost always keeps a eye on him. He shuts down quite a bit because he forgets to get coal and water for himself let alone any food.
Humanoids though are connected to their engines in a way. They can feel if their engines get damages or anything like that. Though when their engines get fully scrapped the humanoid doesn’t die but feels horrible pain as their engine gets fully ripped apart but once their engine is fully scrapped they don’t feel that pain anymore but they end up feeling something part of them is missing.