I’ve heard building mechas is really difficult but there is no problem in building small humanoid robots (Boston Dynamics). So can’t we just upscale them and make mechas this way?
In: Engineering
TL;DR: this is a material problem. A given material can only take so much force and as you scale things up, the forces climb until they just destroy any material you try to use.
This is a great question and applies to a lot more than just mechas (although mechas are certainly one of the coolest applications). The problem of scale can be seen in things like single cell organisms, more complex life, and even buildings and architecture. The scale of all of these things isn’t an accident.
Someone with a similar thought to yours might ask “Why haven’t some animals become enormous? Why can’t living things grow to the size of planets?” The reason is because of some very fundamental properties of physics. When you encounter something you perceive as solid, what you feel is that the molecules in that object are packed very closely and therefore attract each other strongly with different types of forces. These forces have a specific strength based on the shape and size of the molecules or atoms composing the solid.
If you scale this idea up, the hardness of an object depends entirely on how strongly the molecules inside it hold together. Now, let’s take steel. The molecules in steel pull together at a specific strength. From a mechanical perspective, there are two primary ways to apply force to this steel. These are compression (pressing down) and tension (pulling on both ends). For both types of force, there is a maximum tolerance based on the material you use. This tolerance would be higher for steel than paper because the molecules hold themselves together more strongly in steel.
With this knowledge, we can consider a giant, awesome robot. Well, what do we make this robot out of? Metal, probably. A paper robot would fall apart pretty quickly. What kind of metal? Well, probably a strong but light one? In that case, a good candidate would be titanium then. Now, let’s try making a gigantic robot. Well, what we find is that the bottom of the robot is being compressed by everything above it and any hanging parts are tensioning the parts from which they’re hanging. No matter how thick you make certain parts, others will be bearing its load. Now, it would probably be possible to create a robot 20 feet tall, but certainly not 100 or more. The design considerations for moving components under that much load simply defeat the capabilities of modern materials.
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