Lol, interesting. I was thinking of starting a thread like this since I'm looking for inspiration for my killer robots game (the one that the avatar comes from). I was also going to do something with giant robots for my thesis too, but due to a bunch of issues, I have to choose something else
Anyway...
Giant robots in movies and anime are lame. They have this tall thing and what does it do? Shoot lasers and guns and missiles from their body. It's a waste!!
No, a giant robot should do what a person can do, but better! A giant robot shouldn't be 20 meters high, just about 10 meters would do. Too big and it'll be like fighting off ants. You want it to have the advantage that humans did throughout their early years.. where they fought off dinosaurs with obsidan swords.
A giant robot needs to utilize its strength and computational powers. The control systems allow it to wield anything as a weapon - you should give it claws for melee attacks and let it rip apart buildings.
Legs are a disadvantage for balance.. but give three advantages:
1. Better force (torque): They can swing things much better than any wheeled device.
2. Speed/weight: higher center of gravity, but they can walk over small obstacles
3. Dodging: Tanks can not dodge. A giant robot, with a giant computer in its head can anticipate attacks, calculate the possibility of success when dodging, calculate the perfect dodge, and the effects of a misdodge. With legs, it can twist its body to deflect AP missiles. Like a human who can block arrows!
With all these advantages, they should only be as big as needed to give it the strength.
Giant robots are not battlefield devices, like tanks or infantry. They are SIEGE devices. They can smash tanks, throw them, easily smash walls with no ammunition. They are thick enough to handle some heavy damage.
Power is a severe disadvantage, but cold fusion should be available by 20XX. The biggest problem with giant bots are humans. Humans heavily limit its computational potential and speed.
Since we're not just talking about giant robots, I offer a better, cheaper alternative: Small bots.
These things will be small, and inter-connected by a wireless LAN in their heads. They can be equipped with any small weapon, bullets, or simply claws. They're perfect for urban combat. They can crouch quietly near bins. When detecting an opponent, they can alert the others to its presence and strike.. like zerglings, but with more strength, power and speed. With a proper processor, they can even dodge attacks as mentioned above.
What's cool is that our technology is not far from making them as it is.