What are the obstacles in making giant robot combat practical besides the square-cube law...

That's not how planes work.

Giant robots are terrible. Without outrageous energy shields or some other caveat, they have no purpose on a battlefield.

Small fire support robots like Gekkos from MGS are a far better idea.

That said, rule of cool trumps all. I recently played a giant robot fighting campaign inspired by Pacific Rim using Legends of Wulin rules and it was fucking awesome.

It's also nearly impossible to make them walk. Get an action figure, pull one leg forward at a time from the articulation points and try to walk. It becomes like a game of QWOP and will look awkward no matter how good your pilot gets at it. Bipedal bots are simply unnecessary. Look at how insanely difficult it is to get Asimov to walk.

Heat buildup.
As mentioned, the engine is going to be massive and a giant engine will have horrible overheating. This is made even worse since a mech has way more moving parts than a tank.

Other than the square cube law? That's a pretty big one right there.

Energy density: the weight and fuel required to generate enough power is a problem. You can do it, but not enough to meet the needs of combat.

Complexity: only very recently have computers and balancing systems managed to tackle even human-sized bipedal locomotion. Let alone giant-sized robots in combat conditions. The mechanical complexity of a legged drive is very high, too.

Speed: a leg can only swing so fast. So very large machines don't move proportionally faster, and a running gait is right out. Admittedly, this derives a bit from square-cube, but it's a major issue.

Interface: the devil's in the details. Ever watch a baby learn to walk? There's a lot of footwork that we take for granted, beyond "go forward" or "turn right". And no good way for that to translate in a control system, other than to automate it away.

Lack of need/expense: We have tracks and wheeled vehicles that can serve all these needs. If necessary, we can use helicopters. What do walkers do that these can't? Even if hypothetically a mature system would be superior, that would take longer and be more expensive than doing without or using an existing system. This is called a competency trap-- it happens even when the alternative technology will eventually be far superior because extant tech is so far developed that it's good enough.

I'm building a game based on the Podfall CYOA. People get sucked into pods at random and are given Warframe-like biosuits along with a transforming mecha, then turned loose to their own devices. There's a very good reason why the pods give you a mecha, which relates to why the pods are falling to begin with, but the game solves all these problems by making the mecha considerably more advanced than earth tech. If the alien had made non-transforming tanks, they'd be even better, but those aren't in the cards so mechs rock vs everything else in the setting.

Notice something about your OP pic?

You've got huge legs, normal arms and head... and a very very small torso. Why?

In most mecha (and for that matter most of the animal kingdom) the torso contains all the energy-producing and distributing components of the body: digestive system, respiratory system, metabolic controls, and a circulatory system to get all that energy out to the limbs to power operations.

So a body plan like that in a giant robot implies a VERY powerful and compact energy source, one close to the limits of what the mecha's systems can reasonably use. If power were limited, it would have a bigger torso to accommodate a larger engine. Those long legs clearly aren't there because the designers wanted to sacrifice mobility. This is a fast design. A scout might sacrifice armament (no visible weapons!), and maybe there aren't defenses like shields that require power output, so you can't rule out this being a scout model, but even then it clearly has a potent source of energy (eg fusion).

The large feet make sense; like any ground vehicle, you have to watch ground pressure (weight / surface area of the feet). A 60 ton M1 Abrams has 8000 square inches of contact with whatever it's driving on, for a ground pressure of 15 lbs/inch^2 (about double that of a human). So a 60 ton mecha needs 4000 in^2 per foot to give the same 15psi, or 8000 per foot to match a human's performance in the same terrain.

The presence of what appears to be jetpacks doesn't tell me anything. Since there are mechanical limits on walking/running speed, a jetpack can easily be justified as a means for surpassing even what this design's long legs can accomplish, or quickly traversing terrain, or permitting an air drop insertion.

The spike at the top is clearly a sensor mast.

Why are you asking, anyway? Idle curiosity or world-building and looking for a way to explain mecha?

Use the jetpack to reduce ground pressure? Add some thrusters on the front to balance out horizontal forces and you're set.

Of course then why use legs at all if you can just use more thrusters, and you end up with a Starfury optimized for flight in-atmo.

You start by picking an example that is not literally powered by God and his Chosen Agent on Earth.

That God chose His vessel to be a giant robot is really secondary to this.

>So a body plan like that in a giant robot implies a VERY powerful and compact energy source, one close to the limits of what the mecha's systems can reasonably use. If power were limited, it would have a bigger torso to accommodate a larger engine. Those long legs clearly aren't there because the designers wanted to sacrifice mobility. This is a fast design. A scout might sacrifice armament (no visible weapons!), and maybe there aren't defenses like shields that require power output, so you can't rule out this being a scout model, but even then it clearly has a potent source of energy (eg fusion).

Its flight capable and its not a scout. It does not need weaponry. It tears mechs, fortifications, and whole ships apart with its bare hands because it literally runs on der Wille zur Macht. Even its movements are controlled by the pilot's mind and its awareness is shared with him.

I was thinking using the jetpack to traverse rivers and ridges. You're right that if I have that much power and thrusters are that compact and reliable, then I might as well use a VTOL. This came up in a thread yesterday-- if you have grav tanks, then you really don't need mechs or anything else. The same principle applies to easy reliable survivable sustained VTOL.

So instead we have the setting limited to BT-like jump jets. My mech can handle normal ground. Jets will get me across short stretches of impassable terrain. If I sink into soft ground, the jets can get me clear. But I can't just fly around everywhere.

Ahh so it's a supermech powered by plot. Obviously we're talking at least moderate levels of realism. If the setting is soft enough, then why bother with rationales at all?

youtube.com/watch?v=g0TaYhjpOfo

Before you even start trying to build a giant robot you have to first overcome the problems of robotic walking, which is something very smart people have been trying and failing to do for decades. Given the rate of progression in that field robots are going to be falling flat on their asses when trying to do simple tasks for the next 40 years at least.

Human-like range of motion and balancing ability aren't a given and don't exist in modern robotics.

They started off closer to hard mecha, and the protagonist being a martial artist (admittedly he can also throw Hadokens around..) simply never adapted to using weapons. Offensively he's toward the middle of the pack but had an extreme mobility advantage.

Come disc 2 is when they upgrade entirely to plot powered supertech, hence the mind controlled mechs, the unlimited energy systems, etc etc etc.

The civilization that all this tech came from is about 5000 years in the future from us and discovered a fourth dimensional being trapped inside a billions year old construct for ???? reasons.

They basically used the equivalent of God as a power source and reverse engineered a lot of tech from discoveries they made on this artifact. Its why all the tech seems ridiculous, because it really is.

Fast forward another 10,000 years, all that tech and god-as-a-battery have been scattered across a distant world. Humanity rebuilt with what they could scavenge, and so we get way lower tech levels. The current timeline is almost like early 1900's only giant robots dominate the field of combat because they keep excavating ancient robots from out of the dirt and refurbishing them. Its very anachronistic but kind of cool.

>planes
>getting shot down by rpgs

What? Are you retarded?

That's not how planes work

I like the way you think, user.