[scanr]

You're right that it's unlikely that the current generation of mechanical 'robots' will be able to effectively take over.

We are looking a future where we'll have armed AI e.g.:

http://motherboard.vice.com/en_uk/blog/the-pentagons-vision-...

That said, even without weapons, a Strong AI could probably just manipulate humans into self destructing. Given the amount of effort going into machine learning to convince humans to buy things, I suspect it won't be much of a stretch for a Strong AI to switch to more nefarious objectives.