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Let's assume you have access to some pretty crazy tech but that you still have to obey the basic rules of biology. If you build your cyborg so that the only remaining squishy bits are the brain and perhaps a few others like the heart and digestive system (though it is my understanding that everything but the brain should be theoretically optional as long as you have mechanical analogues that can provide nutrients and oxygen to the brain), your tin-man will obviously be physically superior to a normal human. That goes without saying. But can they catch a bullet?

While a sufficiently sturdy machine should be capable of doing this (I think), the brain obviously isn't. Even if we assume you've overclocked your organic brain's processing power with some form of nanotechnology or additional cybernetic enhancement so that it can react in time to dodge a bullet, the g-forces you'll be subjecting it to by moving it out of the way of the bullet's projected flight path (even by a marginal amount) will turn that poor defenseless lump of meat into a skull full of jelly. That's why you don't DODGE the bullet. You catch and/or preferably deflect it, only moving your completely mechanical limbs and sparing your squishy head from having to accelerate to a few thousand gs.

But does that really work? Would simply moving one of the mechanical parts of your body at high speeds to intercept a fast-moving projectile keep your organic body parts safe from the strain you'd otherwise be putting on them, or is this just a drastic oversimplification of the forces acting on this cyborg when they attempt to catch/deflect a bullet without moving their head or neck?

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    $\begingroup$ Seems like three separate --but related-- questions: 1) Detecting the projectile far enough away and accurately enough to forecast the movement required, 2) Speed and accuracy of your manipulator(s) required to move into position and grab the projectile based upon the detection, and 3) Force of your manipulator(s) required to absorb the kinetic energy of the projectile during the follow-through of the catch without damage. $\endgroup$ – user535733 Apr 11 '17 at 4:40
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Yes that seems perfectly possible with some slightly futuristic tech, you would just need sensors that can detect a flying bullet (already possible today) and limbs that can move fast enough and are strong enough to catch and stop a bullet.

The stopping part seems doable (the kinetic energy of a bullet is not that high), as for the fast enough part if your wold is advanced enough to build cyborgs it wouldn t be crazy to think that we can manufacture limbs that can move super fast .

The thing is that the reflex of catching shouldn't be processed by the brain because as you mentionnend the brain can t process it fast enough. I would be a separate autonomous system of sensors that would automatically activate the limbs to catch any incoming projectile.

However in a world where such technology is available, it would probably not be really usefull as a way to protect your cyborg because the attackers would probably use different "anti-cyborg" weapons. You can use your imagination to come up with such a weapon (lasers/emp ...) .

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A slightly different idea that might be good enough for your purposes might be to begin performing the stop / dodge manoeuvre before the shot is actually fired. Using cyborg-level vision and decision-making you could begin to move the cyborg's body out of the way while the operator of the weapon is still in the process of squeezing the trigger, or at least deciding to.

According to this totally scientific resource I found (http://www.sciforums.com/threads/reaction-time-for-pulling-a-trigger.61311/) you have about a quarter second (0.25s) between the shooter deciding to fire and the round actually going off. A quarter second is more than enough time to move a human torso out of the way or lift a (well-armoured) hand.

Couple this with your cyborg's ability to very accurately detect the orientation of the weapon and the bullet's subsequent trajectory you easily have an entity that is very, very hard to hit at close range.

For longer ranges you've got fewer options at your disposal (you don't really have the option of using vision to detect the shooter's intentions and a high-powered rifle bullet will easily exceed the speed of sound) so you've pretty much got to resort to some very high-fidelity radar to detect the incoming bullet and begin proceedings.

The whole idea of this proposal (dodging the shot rather than the bullet) is the vastly greater time your cyborg gets to move, meaning that the few meat parts of this cyborg individual left are only subject to fairly ordinary accelerations / conditions.

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  • $\begingroup$ I'd like to imagine that, similar to what they tried to explain with the Robo Cop remake, the meat brain was cut out of the decision making process in combat, meaning catching the bullet was an automatic and AI driven response. $\endgroup$ – Marshall Tigerus Apr 11 '17 at 18:42
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Bulletproof vests already do it: catching a bullet and dissipating its kinetic energy away from vital parts of the target. Yes, the target wearing the vest still get "punched" by the momentum of the bullet, but it is way better than having his/her body internally dissipate the energy of the bullet.

Moreover for close range shots there is almost no time to react and move the limb: for a shot fired at 20 m, with a speed of 200 m/s, you have only 0.1 s to have the limb in place to protect you (if you see the gun pointed at you) or even less if you have to react to the sound of the shot being fired (which reaches you at about 300 m/s).

Therefore, instead of using the cyborg limbs to catch a bullet, equip its body with something similar to a bulletproof vest/armor.

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    $\begingroup$ Please keep in mind that MathJax comes at a cost. It's a great feature when needed, but shouldn't be used in situations where all it adds is a different font. $\endgroup$ – a CVn Apr 11 '17 at 6:17
  • $\begingroup$ @MichaelKjörling, got it $\endgroup$ – L.Dutch Apr 11 '17 at 6:17
  • $\begingroup$ FWIW, at 300 m/s, the sound of the shot moves 20 meters in 67 ms, and the bullet needs 100 ms to move the same distance. That leaves about 33 ms to intercept or evade the bullet, assuming that you're able to determine the bullet's trajectory accurately enough from the initial audiable shockwave alone (which I would consider doubtful). $\endgroup$ – a CVn Apr 11 '17 at 6:20
  • $\begingroup$ I ended up asking a related question about How quickly could a cyborg determine that a bullet has been fired from the sound alone? $\endgroup$ – a CVn Apr 11 '17 at 6:31

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