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This question already has an answer here:

I have a series of humanoid combat robot dubbed the Atlanta-Types created specially to fight someone (codenamed Heracles) with the powers of electrokinesis and Low-Mid regeneration on equal footing. The Atlanta-Types are equipped with several features to combat Heracles including an electrically resistant exoskeleton, an aerodynamic body, carbon nanotube muscles granting them incredible strength and four rotating missile-launchers housed in the torso serving as their primary armaments.

However, each missile launcher contains a limited number of micro-missiles and an Atlanta-Types can go through them very quickly. In order to compensate for this drawback, the Atlanta-Types have been outfitted with a pair of forearm-mounted superheated stabbing blades composed of a Coltan-Titanium alloy and capable of reaching temperatures of 1,000°C. These weapons are necessary for negating Heracles' healing factor, which can quickly heal lethal wounds and coupled with his enhanced durability, makes him somewhat difficult to kill.

When I was deciding upon what sort of blades the Atlanta-Types would have, I came across several photos of the NERV-made Anti-G Weapon. The Anti-G Weapon has a large pair of triangular arm blades that fold up against the elbow when unneeded.

Blades deployed and folded up

Although, I'm greatly concerned that these blades will greatly affect the Atlanta-Type's acceleration rate by creating extra drag when running. What would be the practicality or impracticality of such a weapon?

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marked as duplicate by Aify, Frostfyre, Renan, JBH, Mark Olson Jun 7 '18 at 19:20

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ I took the liberty to replace your chest-blaster tvtropes link with a link to your previous question, as far as I understand they are both about the same robots - so that gives some more views, etc. to both :) $\endgroup$ – dot_Sp0T Jun 7 '18 at 10:12
  • $\begingroup$ Also, recommended reading: worldbuilding.stackexchange.com/questions/62638/… $\endgroup$ – Aify Jun 7 '18 at 17:33
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The blade itself, or presence thereof, would not really slow down the accelartion unless the robot is capable or near super sonic speeds, then maybe the blades would create enough drag to count.

Yes, the blades would create drag, and the extra weight would need to be accounted for as well, but not to the point where it would be really noticeable and the downside of the speed loss would be more than compensated by the pros of having a weapon that doesn't require ammo.

However, when a humanoid walks, it swings its arms opposite to its legs, to counterbalance the movement. Adding weight to the arms may actually be off benefit for increased speed. (I can't say that for sure, a smarter person would have to correct me if they can do the math.)

Super Heated Blades... it's just Cons for fighting

If this was for general sword fighting, then the super heated factor is unlikely to add any benefit, although 1,000°C is very hot for organic matter, but if you get a knife red hot and then slash at butter, it doesn't go in much further than a cold knife, due to transfer of heat not being all that quick, whereas a hot knife pushing constantly against butter will go through much easier, as it has time to heat and soften the butter as it goes through. It's a simple experiment you can even try at home (butter, knife and a blow torch).

And if we presume this Heracles would be wearing some form of armour, it is not hot enough to soften any metals that would be used in advanced armours even if held touching the hot metal to the armour for some time. So in theory it's creating a large amount of work and energy into the design and operation of a weapon that is at best marginally better then a standard cold blade.

Suggestion

Save the energy and design time you would put into heating up the blade, and put that into the agility of the robot. The faster you can swing that sword the more effective it can be... so long as it can handle the impacts involved in robot sword fighting...

or...

Have the sword contain super heated plasma (roughly 8,000°C to 10,000°C). Then if you successfully stab through the armour of the Heracles then you could vent this plasma inside the armour. Doesn't really matter how well the healing factor is of the Heracles... it would be a struggle to compensate for the extreme heat being pumped inside it and then insulated between the armour and organic matter. It would also be effective against other robots, if you could punch through the armour, then vent the plasma inside all the complicated circuitry would be destroyed pretty quickly, and solders will melt away, circuit boards would melt - everything would melt or catch fire or start loving Justin Bieber. Just an all around bad day for the victim.

It also wouldn't affect the operation of the weapon that much, but could easily deliver a crippling blow to the enemy.

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  • $\begingroup$ Nice suggestion, and a very cruel one... starting to love Justin Bieber... there's gotta be some kind of war convention forbidding things like that ;) $\endgroup$ – Sec SE - clear Monica's name Jun 7 '18 at 11:15
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    $\begingroup$ @Secespitus: I think technically it would be covered by the Geneva convention, under the cruel and unusual punishment section, but i'm pretty sure weaponized robots would be in there somewhere as well... so if you're gonna break the convention in the first place... why not go all in $\endgroup$ – Blade Wraith Jun 7 '18 at 11:55
  • $\begingroup$ "If you are going to hell for one sin anyway, why not commit a thousand and come here as a hero?!" $\endgroup$ – Sec SE - clear Monica's name Jun 7 '18 at 11:57
  • $\begingroup$ "It's a simple experiment you can even try at home (butter, knife and a blow torch)." - Just keep in mind that this will ruin the blade. $\endgroup$ – Ruther Rendommeleigh Jun 7 '18 at 12:23
  • $\begingroup$ @RutherRendommeleigh: Very True, don't do it with your best silver! Reckon i should edit that into my answer? $\endgroup$ – Blade Wraith Jun 7 '18 at 12:35
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At the risk of moderator ire for both answring and VTC as a duplicate, please note that any metal strong enough to withstand the heat necessary to melt your opponent's armour is likely strong enough to pierce the armour without the benefit of said heat, allowing you to reduce the weight, complexity, and energy consumption of your robot, making it more efficient.

It's almost impossible to scientifically justify the visually cool things regularly associated with cartoons. A cruise missle can readily disable overly complex mecha of any kind. Sorry.

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Blade Wraith already has a very good answer covering both the aerodynamics aspect (not likely to be an issue at subsonic speed). That answer also covers some of the issues of using high temperature blades as weapons. There is however one point I would like to add, and I have some suggestions for alternative uses for all that energy.

First, beyond what the aforementioned answer says, you also have to consider that getting blades that aren't affected by that much heat is not going to be cheap. 1000 degrees Celsius is getting close to the typical temperature range used for tempering most types of steel that are used for blades, so in an ideal situation, an alternative material would be better, which is likely to raise the cost significantly.

Now, as far as alternatives, you have a couple of interesting options:

  • Make the blades vibrate at ultrasonic frequencies. Cutting things is largely about displacing material. Making a blade vibrate very fast improves it's ability to displace material. It also gives a nice indication that it's dangerous (you can probably hear the low frequency harmonics as a high pitched whine), helps keep it clean (most things will just fall off), and can cause a whole lot more damage to organic tissue. If you really want physical blades, this is probably the best option (though you will need special materials for the blade, and proper mechanical isolation from the rest of the mech).

  • This is a bit of a cliché, but give it lightsabers instead. At it's core, a lightsaber is just a plasma cutter with a very long stream, which recirculates the plasma using magnetic fields and thus uses limited energy when not cutting anything. Such a device is actually technically possible with real world tech, it's just prohibitively expensive and would use an insane amount if energy. This would be easily able to cut through most armor, and trivially slice through organic matter. It would also provide similar incendiary properties, and wouldn't affect aerodynamics at all when not in use.

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  • $\begingroup$ IIRC evangelion’s “progressive knife vibrating blades was $\endgroup$ – Dan W Jun 7 '18 at 18:22
  • $\begingroup$ Sorry, hit send by mistake on my tiny mobile keyboard... IIRC, evangelion’s “progressive knife” was a vibrating blade. $\endgroup$ – Dan W Jun 7 '18 at 18:23

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