Pop culture is littered with tons of giant robots, which most of us probably grew up with. It is literally impossible to not know who Voltes V is. The same applies with Optimus Prime, Voltron, and all those Gundam models to name a few. These fictional characters became the embodiment of cool, saving all of humanity and the world and all that. While given all the recent innovations in technology, are creating giant robots really possible?
In advent of Pacific Rim's success, a recent article discusses the possibility and physics regarding these kinds of robots.
Given a scientific perspective, these robots may just be purely fictional. Giant robots poses a lot of problems given the parameters of physics. First, the increase in their size, which may give them additional strength, will also give them additional drag. Thus, this will decrease the speed of their movements and with each movement they make, they will need more energy to do so. This then poses another problem, energy source. These robots are usually powered by some fictional source, like the magical Allspark, and even with all the innovations in the field of nuclear energy, replicating their power is still impossible.
Choosing the right materials for production is also challenging, as most existing materials may not be suitable. Steel, titanium and beryllium and carbon reinforced plastic are among the options. However, they may not provide the strength, rigidity, lightweight-ness it needs.
Perfecting a robot's motor skills is another problem most engineers and scientists encounter. Even the existing robots took years to polish, so applying such technology on a larger scale would be more difficult.
To say that these giant robots would remain as a figment of our imagination would be too harsh of a judgement, considering how several millenniums ago, most of the machines we take for granted everyday were deemed impossible. Though it would take several more years for scientists and engineers to develop giant robots, they're still my first bet when some apocalyptic threat to humankind occurs.