The original version of this answer is here.
Nothing on Stack Exchange has copyright protection, which is good and bad
I posted a question about my original answer at Law.SE. That answer is well informed and very much worth reading by anyone who uses Worldbuilding.SE with the worry that they may be restricted in any way by using ideas found via this Stack.
In a nutshell: you have no problems. People who post answers are posting them gratis and your use of those answers to guide your writing efforts leave you in full control of your copyright without dependence.
Further, the author of the Law answer posted a question and answer concerning co-authorship and derivative works that will also be valuable to the practitioners of the arcane art of Worldbuilding.
The CC-BY-SA license
Proponents of the license will remind you that nothing about that license stops you from using what you learn from here commercially.
While you have no copyright problems at all using what you learn here in your writing, neither does anyone else. Granted, you can't copyright the idea of FTL travel, but you can copyright the phrase, "the HGP intersplit engine." So long as the idea came from Worldbuilding and the name came from you, you have absolutely no problem. But, as was mentioned over at Law.SE, due to the Creative Commons licensing, even if you got a cool proper noun from here, you won't have copyright problems — other than you can't stop anyone else from using it, either.
In another nutshell: the more specific the wording you take from Worldbuilding, the harder it will be for you to protect your copyright if someone else uses that same wording. If you took an idea and crafted that idea to make it your own — you're in like flynt! Because everything you do to mold it to your story makes it ever more unique.