system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: With all the advances in technology, why have we not even come close to replicating exoskeletons like the Iron man suit?

I know exoskeletons do exist out there, but most of them are impractical or really limiting in one regard or the other. What is limiting our ability to make something as efficient?
gpt
A power source with a great enough power-to-weight ratio is one thing. The best we got is gasoline, but gas and combustion engines are heavy unless you're on the scale of a weed-wacker.

Next after that is power transmission: taking energy from the motor and putting it in your arms and hands. Either this is done with relatively slow electric actuators, or very heavy but highly efficient and fast hydraulics. You could do it with electric motors and transmissions, but that would require far more electricity than what's portable for even an exoskeleton.

Iron Man's suit appears to function with the power and accuracy of encoded induction motors comparable to CNC machine tools, but small enough that they have a form factor like a wrist watch or kneepad. This is far out of the reach of modern technology and may be that way for some time. Problems like these aren't matters of making things smaller like in computers. (So Obadiah Stane was wrong on at least one front.) Mechanical issues like these are matters of increasing pure material properties like energy density in batteries, conductance in wires, and compressive strength in structures.