Fish out of Water: Time/space traveler from Earth as a background

[Grynning]

Newest article on Forgot My Dice is a classic trope. I love the artwork this week:
http://forgotmydice.com/index.php/2016/08/15/tis-new-to-thee/

[khadgar567]

this gets broken real fast think about modern enginer for mega structures if that bastard goes middle ages and decide to use his knowledge to build fort knox you have a problem which is self sufficient castles that can't be seiged if more people choose this background we can say sayonara to the camping world just add mechanics student now our fort has turrets can kill nearly every regular foe

[Griss The Gnome]

this gets broken real fast think about modern enginer for mega structures if that bastard goes middle ages and decide to use his knowledge to build fort knox you have a problem which is self sufficient castles that can't be seiged if more people choose this background we can say sayonara to the camping world just add mechanics student now our fort has turrets can kill nearly every regular foe

A) To be fair, Fort Knox isn't that secure. What makes it hard to get into is that it's in the middle of military base, and what it is holding is heavy as hell, and would require several days to move. Thats why Goldfinger the book had the villain trying to steal the gold, and Goldfinger the film changed it to irradiating it. Because a vault of that size couldn't be emptied in a few hours.
B) The background feature says with DM approval, so if your worried about it, don't let the character do it. Ash Williams converted his gas car to a steam car in like two days or something. It's a funny movie, if your D&D campaign is more gritty then yeah, don't allow it.
C) D&D is already an anachronistic setting, so a character builds an earth turret, swell. Earth technology has never had to deal with dragons, Wizards, Orc Hordes, Divine Avatars, and other D&D problems, so it's probably not that good in practice.