I'm trying to get a general idea of the development of arms and armour throughout history. Not just the types of armor used. That I can find with a simple google search. Rather what caused the evolution and all kinds other factors.
Such a question alone, breaks this subs rules. Recently I made a try at narrowing down a timeline and geographical area. Backfired somewhat. So I'm wondering.
How should I approach this? What kind of timeline and geographical constraints should I place for the questions?
In addition to what /u/The_Alaskan and /u/Georgy_K_Zhukov said, you could try using Google to find previous comments on this and related subjects. Browsing those might give you an idea of what to ask for.
If you add "site:reddit.com/r/askhistorians" to your search terms, it will only return results from AskHistorians. This search seems very promising:
armor development site:reddit.com/r/askhistorians
As for narrowing questions down, your previous attempt wasn't all that bad. The only thing is, once the question is opened the body of the question contains 8 more questions! If anyone has something to contribute in reply to the title question, seeing those additional questions ranging from materials used to socio-economic structures might discourage them.
You're probably better off asking one or two questions, saving the others for follow-up questions or other threads. This is not guaranteed to get you an answer, but it will improve your odds.
If you're asking that general a question, this probably isn't the best place. You'd have better luck if you went to the library first ... now, if you were looking for recommendations on what to look for in the library, I think this is the right spot.
I would say you want to focus on a specific period or time span, or even better, region (at least to a continent!). "How did the standard issuance of arms change for a European army between the late-medieval period and early-modern" for example.
Whether a question gets notices is sometimes a crap-shoot. Some get upvoted, some don't. And even if they do, doesn't mean the right guy will show up to answer it. Looking at your last submission, you are going about it the right way, but really, the more specific you get, the better chance of an answer you get. Specific time and specific place is really the best for question. Just gotta have a little patience, and hopefully it'll pay off!