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Batman Grappling Gun

Posted: Tue Feb 09, 2010 8:48 pm UTC
by Batkram13
So, I'm sure everyone has at one point wished they had a grappling gun like Batman, and then been devastated to find out they don't actually exist (in the ease that the movies and comics portray them). But I feel like with the advent of carbon nanotubes, such devices could be theoretically buildable. So my question is, what do you guys think it would take to get a working Grappling gun, that is relatively small.

My idea for the design consists of a spool of cable, wound from these carbon nanotubes, attached to a hook which is magnetically accelerated. Then it would need a motor to rewind the cable, and strong enough to pull a person up a building at a reasonable speed. Compressed air is the commonly used launcher in the comics, but I wonder if that is as efficient as an accelerator, or as reusable. Then there's the fact that the hook may not catch. Could some sort of electromagnet be attached to the end instead of a hook?

Re: Batman Grappling Gun

Posted: Tue Feb 09, 2010 9:05 pm UTC
by thicknavyrain
First of all, I love you, second of all, I get the feeling it would have to have some sort of fuel to fire it out at such a fast rate, so it would need some sort of chemical/explosive propellant in order to make it go fast enough. Another question is, what if the hook goes way past the ledge you want it to hook onto? There needs to be some sort of button or trigger to stop/decelerate the line/reel so the hook can catch onto the ledge quickly, if I explained that well enough that is. I like the idea though. Did I mention how cool a topic this is?

Re: Batman Grappling Gun

Posted: Tue Feb 09, 2010 9:21 pm UTC
by TaintedDeity
There's an interesting Mythbusters experiment about this.

Re: Batman Grappling Gun

Posted: Tue Feb 09, 2010 9:58 pm UTC
by Batkram13
Yes, I assume a gas propellant would work. But I wonder if a magnetic accelerator, like in rail guns wouldn't be more efficient? Or at the very least more reusable.

Also, I saw the mythbusters thing a long time ago, but wasn't that more of a rappelling device?

Re: Batman Grappling Gun

Posted: Tue Feb 09, 2010 10:25 pm UTC
by thoughtfully
Rail guns are not more reusable. They require maintenance every couple of firings, typically. Not to mention any sufficient power source would be super bulky! They also work better when the have some length over which to work. I'm not sure how compact you could make a useful rail gun, but there is a limit. Much better to use some sort of a charge (compressed gas or explosive) that can be easily reset from spares on your belt. Sometimes (frequently, actually), old tech is better, more reliable, and easier to use.

The bit that bugs me all the time is the nasty jerk at the end when the slack in your cable runs out. You need a really elastic cable if you want to stay attached to your arm!

Re: Batman Grappling Gun

Posted: Tue Feb 09, 2010 11:08 pm UTC
by Meteorswarm
Why wouldn't a thin steel cable work? You wouldn't need to lift more than 250 lbs for a fit person, even loaded with equipment.

Re: Batman Grappling Gun

Posted: Tue Feb 09, 2010 11:25 pm UTC
by Batkram13
Ok so I just saw this.

http://www.uberreview.com/2008/02/tacti ... ok-gun.htm

That device is on the right track, but it's nearly 20 lbs and close to 4 ft long. I imagine that a lot of that length comes from the rope that it uses. It also only shoots the hook, so you'd then have to climb the building yourself.

Re: Batman Grappling Gun

Posted: Tue Feb 09, 2010 11:54 pm UTC
by Kow
You mention carbon nanotubes like the rope is the problem with the design.

Re: Batman Grappling Gun

Posted: Fri Feb 12, 2010 6:16 pm UTC
by oxoiron
Meteorswarm wrote:Why wouldn't a thin steel cable work? You wouldn't need to lift more than 250 lbs for a fit person, even loaded with equipment.
What is your definition of a fit person?

Re: Batman Grappling Gun

Posted: Sat Feb 13, 2010 6:48 am UTC
by Tass
oxoiron wrote:
Meteorswarm wrote:Why wouldn't a thin steel cable work? You wouldn't need to lift more than 250 lbs for a fit person, even loaded with equipment.
What is your definition of a fit person?


Fine make it 500kg to have some safety margin. Steel, kevlar or spectra would still work just fine.

Re: Batman Grappling Gun

Posted: Sat Feb 13, 2010 7:45 am UTC
by Cobramaster
Yeah as far as a delivery system is concerned using a "blank" bullet would be your best bet due to the reliability and energy density, plus almost all of the energy will be used to propel the hook. And as the Mythbusters proved a system capable of pulling you up is not that large at current off the shelf tech levels. Plus outdoing the Mythbusters on a design is not that difficult especially if you have the same budget.

Re: Batman Grappling Gun

Posted: Sat Feb 13, 2010 7:59 am UTC
by PhoenixEnigma
oxoiron wrote:
Meteorswarm wrote:Why wouldn't a thin steel cable work? You wouldn't need to lift more than 250 lbs for a fit person, even loaded with equipment.
What is your definition of a fit person?

More importantly, what are the forces acting on that person? A line with tensile strength of x Newtons will hold about 0.1* x kg hanging vertically without snapping, but forget about any kind of swinging or the like. If you want to be able to use this in a super hero fashion, you're probably going to want to be doing things a hell of a lot more dynamic then dangling there. I think it's important to define our requirements before discussing approaches.

For example:
What kind of range does our device need?
Does it need to be able to place an anchor into an object, or simply over one?
What is the mass of the user and their equipment?
What actions should we expect the user to take, and how will stress the line, launcher, and anchor?
Does the line need to withstand only tensile forces, or shearing ones as well?
Does it need to be self-retracting? If so, at what speed, and how much control is required?
What are the objectives for stealth, reusability, and portability?

Re: Batman Grappling Gun

Posted: Sat Feb 13, 2010 7:52 pm UTC
by Meteorswarm
PhoenixEnigma wrote:More importantly, what are the forces acting on that person? A line with tensile strength of x Newtons will hold about 0.1* x kg hanging vertically without snapping, but forget about any kind of swinging or the like. If you want to be able to use this in a super hero fashion, you're probably going to want to be doing things a hell of a lot more dynamic then dangling there. I think it's important to define our requirements before discussing approaches.
Let's use the "typical" use shown in Batman. I'll do my best with my memory, and offer some suggestions.
PhoenixEnigma wrote:For example:
What kind of range does our device need?
I'm not sure on this one, but 50-100 feet seems reasonable.
PhoenixEnigma wrote:Does it need to be able to place an anchor into an object, or simply over one?
IMO, over something is probably a better bet. Designing a head that can stick into an arbitrary material with enough strength to hold a lot of weight, and be launched from a small launcher with enough force is difficult.
PhoenixEnigma wrote:What is the mass of the user and their equipment?
We should pick a number for this. I say 250 lbs.
PhoenixEnigma wrote:What actions should we expect the user to take, and how will stress the line, launcher, and anchor?
In my view, I'm seeing shoot, climb, swing a little maybe.

Re: Batman Grappling Gun

Posted: Sat Feb 13, 2010 10:12 pm UTC
by Cynical Idealist
Meteorswarm wrote:
PhoenixEnigma wrote:What is the mass of the user and their equipment?
We should pick a number for this. I say 250 lbs.

That sounds on the low side (the only other number mentioned in this thread, 500 kilograms, sounds like too far in the other direction).

Lets assume a soldier (since grappling guns are likely to find their way into military units first, and thinking of the practical is more fun). To be more specific, we'll assume US Marine, maybe a bit over 6 feet tall, weighing 200 lbs (a bit on the heavy side for someone 6 feet tall, but within acceptable limits, and if they're 6'2" or 6'3", well within limits). For equipment, 20 lbs for the launcher, 16 lbs for the protective vest, 3 lbs for a lightweight helmet, 9 lbs for a loaded m16 (with no extra ammunition!), and we're already uncomfortably close to 250 lbs. Then there's additional magazines of ammo, communications equipment...I'd say that the rope should be able to hold at least 300 lbs of user + equipment, while the user is using a climber to ascend and possibly swinging from side to side. You should also be able to use the same equipment to get back down, so the rope should be strong enough to be used to rappel back down (which will probably cause higher loads than using a steadily moving climber).

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 2:10 am UTC
by Ventanator
Cynical Idealist wrote:You should also be able to use the same equipment to get back down, so the rope should be strong enough to be used to rappel back down (which will probably cause higher loads than using a steadily moving climber).


This.

If you get up, you need a reliable way back down. Also, the engine used in it needs to be strong enough to lower the person. If you're pulled up by the gun itself, that is. If you are pulled up by a secondary device, or your arms, then that wouldn't matter and you could rappel down

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 3:14 am UTC
by Meteorswarm
Cynical Idealist wrote:
Meteorswarm wrote:
PhoenixEnigma wrote:What is the mass of the user and their equipment?
We should pick a number for this. I say 250 lbs.

That sounds on the low side (the only other number mentioned in this thread, 500 kilograms, sounds like too far in the other direction).

Lets assume a soldier (since grappling guns are likely to find their way into military units first, and thinking of the practical is more fun). To be more specific, we'll assume US Marine, maybe a bit over 6 feet tall, weighing 200 lbs (a bit on the heavy side for someone 6 feet tall, but within acceptable limits, and if they're 6'2" or 6'3", well within limits). For equipment, 20 lbs for the launcher, 16 lbs for the protective vest, 3 lbs for a lightweight helmet, 9 lbs for a loaded m16 (with no extra ammunition!), and we're already uncomfortably close to 250 lbs. Then there's additional magazines of ammo, communications equipment...I'd say that the rope should be able to hold at least 300 lbs of user + equipment, while the user is using a climber to ascend and possibly swinging from side to side. You should also be able to use the same equipment to get back down, so the rope should be strong enough to be used to rappel back down (which will probably cause higher loads than using a steadily moving climber).


Well, that's fair, but I think we should separate the extra stresses from the actual weight we want to pull, since the first can be determined from the second. 300 lbs as our user's weight sound ok, then?

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 3:16 am UTC
by PhoenixEnigma
Meteorswarm wrote:Well, that's fair, but I think we should separate the extra stresses from the actual weight we want to pull, since the first can be determined from the second. 300 lbs as our user's weight sound ok, then?

I'd still call that a little low (what if you need to carry an injured person with you?) but it will do as a decent approximation. In a situation like that, you can just rely on your 2x safety factor or whatever.

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 7:29 am UTC
by Tass
Lets look at what rock climbers use. With safety margin, I don't think 5000N is too high, it is still not going to be much of a problem if you only need 30m. Batman doesn't need nanotubes, Spiderman would need it to be able to carry enough of the stuff though.

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 8:13 pm UTC
by Meteorswarm
PhoenixEnigma wrote:
Meteorswarm wrote:Well, that's fair, but I think we should separate the extra stresses from the actual weight we want to pull, since the first can be determined from the second. 300 lbs as our user's weight sound ok, then?

I'd still call that a little low (what if you need to carry an injured person with you?) but it will do as a decent approximation. In a situation like that, you can just rely on your 2x safety factor or whatever.


Ok, I'm not making myself clear enough. I'm saying, let's use 300 lbs as our baseline target weight. THEN, after we decide that, we decide what kind of safety factor we want to factor in based on the expected use cases, for a user weighing 300 lbs.

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 8:56 pm UTC
by Carnildo
Meteorswarm wrote:
PhoenixEnigma wrote:
Meteorswarm wrote:Well, that's fair, but I think we should separate the extra stresses from the actual weight we want to pull, since the first can be determined from the second. 300 lbs as our user's weight sound ok, then?

I'd still call that a little low (what if you need to carry an injured person with you?) but it will do as a decent approximation. In a situation like that, you can just rely on your 2x safety factor or whatever.


Ok, I'm not making myself clear enough. I'm saying, let's use 300 lbs as our baseline target weight. THEN, after we decide that, we decide what kind of safety factor we want to factor in based on the expected use cases, for a user weighing 300 lbs.


Instead of arguing about it, we could see what stresses existing equipment is designed to deal with. I checked a selection of mountain-climbing ropes at REI's website, and they're generally rated for 9000 newtons (2000 pounds force), with the note that they''ll generally stretch up to 30% to absorb the shock from a fall.

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 9:14 pm UTC
by PhoenixEnigma
Carnildo wrote:
Meteorswarm wrote:
PhoenixEnigma wrote:
Meteorswarm wrote:Well, that's fair, but I think we should separate the extra stresses from the actual weight we want to pull, since the first can be determined from the second. 300 lbs as our user's weight sound ok, then?

I'd still call that a little low (what if you need to carry an injured person with you?) but it will do as a decent approximation. In a situation like that, you can just rely on your 2x safety factor or whatever.


Ok, I'm not making myself clear enough. I'm saying, let's use 300 lbs as our baseline target weight. THEN, after we decide that, we decide what kind of safety factor we want to factor in based on the expected use cases, for a user weighing 300 lbs.


Instead of arguing about it, we could see what stresses existing equipment is designed to deal with. I checked a selection of mountain-climbing ropes at REI's website, and they're generally rated for 9000 newtons (2000 pounds force), with the note that they''ll generally stretch up to 30% to absorb the shock from a fall.

That stretching is a major point - that will drastically lower the peak force incurred by spreading it out over a longer period of time. If we can incorporate that in a thinner line (some sort of weaving trickery?), that would be excellent - not only does it reduce forces on the line, but on the person attached to the line as well. Given how thin a carbon nanofibre line might be, stopping it from slicing through things (like users)

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 9:33 pm UTC
by Meteorswarm
PhoenixEnigma wrote:That stretching is a major point - that will drastically lower the peak force incurred by spreading it out over a longer period of time. If we can incorporate that in a thinner line (some sort of weaving trickery?), that would be excellent - not only does it reduce forces on the line, but on the person attached to the line as well. Given how thin a carbon nanofibre line might be, stopping it from slicing through things (like users)


Couldn't you put a sheath around it to make it safer, if that was a problem?

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 9:46 pm UTC
by PhoenixEnigma
Meteorswarm wrote:
PhoenixEnigma wrote:That stretching is a major point - that will drastically lower the peak force incurred by spreading it out over a longer period of time. If we can incorporate that in a thinner line (some sort of weaving trickery?), that would be excellent - not only does it reduce forces on the line, but on the person attached to the line as well. Given how thin a carbon nanofibre line might be, stopping it from slicing through things (like users)


Couldn't you put a sheath around it to make it safer, if that was a problem?

Well, yes, but that kind of defeats the point of using a small diameter line to start with, doesn't it? Unless we have some kind of compressible hollow sheath?

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 11:38 pm UTC
by Matterwave1
Another point to consider is that...is the human grip, for a well trained man, strong enough to grip onto this device one handed while it pulled him up (like Batman does it most of the time)?

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 11:47 pm UTC
by Mr_Rose
Matterwave1 wrote:Another point to consider is that...is the human grip, for a well trained man, strong enough to grip onto this device one handed while it pulled him up (like Batman does it most of the time)?

If you can swing across monkey bars (a semi-standard piece of equipment on an obstacle course) and do pull-ups (a semi-standard part of strength training) you can certainly carry your own weight on your grip. Further training specific to the device wouldn't exactly be far-fetched either. Oh and, for Mythbusters, Jamie was able to use his device effectively despite ostensibly being in late middle age and less than prime condition...
Additionally, Batman isn't always depicted as using the device one-handed; I am pretty sure that it can be clipped to his belt, for instance. Plus I wouldn't put it past him to have some sort of reinforcement in the palms of his gloves that allowed him to lock the grip to the grapnel and possibly lock the glove to the rest of his suit.

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 11:57 pm UTC
by Matterwave1
Ok, seems fair enough. Just, when you're hanging 50-100 feet above the ground, perhaps you want something more than your one handed grip to keep you from falling to your death. (And, yes You can do more than 1 hand, but 1 handed is obviously so much cooler...)

Re: Batman Grappling Gun

Posted: Sun Feb 14, 2010 11:57 pm UTC
by PhoenixEnigma
Matterwave1 wrote:Another point to consider is that...is the human grip, for a well trained man, strong enough to grip onto this device one handed while it pulled him up (like Batman does it most of the time)?

With a suitable grip, I can hang from one hand for a period without terrible difficulty. It's certainly possible, although a simple strap to loop around the forearm would make life much easier.

Anyways, it seems like we're looking for something to project, say, 25m of line, rated to around 9000N. A little research indicated a three-prong climbing hook can probably be made under 200g without any problems.

Assuming we use a material with a tensile strength of 3GPa (of which several materials are available today), I get a required cross section of 0.03cm2 or about, uh, 1mm diameter?

So far, looking pretty realistic :)

Re: Batman Grappling Gun

Posted: Mon Feb 15, 2010 12:52 am UTC
by Meteorswarm
PhoenixEnigma wrote:
Matterwave1 wrote:Another point to consider is that...is the human grip, for a well trained man, strong enough to grip onto this device one handed while it pulled him up (like Batman does it most of the time)?

With a suitable grip, I can hang from one hand for a period without terrible difficulty. It's certainly possible, although a simple strap to loop around the forearm would make life much easier.

Anyways, it seems like we're looking for something to project, say, 25m of line, rated to around 9000N. A little research indicated a three-prong climbing hook can probably be made under 200g without any problems.

Assuming we use a material with a tensile strength of 3GPa (of which several materials are available today), I get a required cross section of 0.03cm2 or about, uh, 1mm diameter?

So far, looking pretty realistic :)


I'd say that, with those parameters, the cable isn't a problem. How small can we get the launcher?

Re: Batman Grappling Gun

Posted: Mon Feb 15, 2010 1:01 am UTC
by PhoenixEnigma
Meteorswarm wrote:
PhoenixEnigma wrote:
Matterwave1 wrote:Another point to consider is that...is the human grip, for a well trained man, strong enough to grip onto this device one handed while it pulled him up (like Batman does it most of the time)?

With a suitable grip, I can hang from one hand for a period without terrible difficulty. It's certainly possible, although a simple strap to loop around the forearm would make life much easier.

Anyways, it seems like we're looking for something to project, say, 25m of line, rated to around 9000N. A little research indicated a three-prong climbing hook can probably be made under 200g without any problems.

Assuming we use a material with a tensile strength of 3GPa (of which several materials are available today), I get a required cross section of 0.03cm2 or about, uh, 1mm diameter?

So far, looking pretty realistic :)


I'd say that, with those parameters, the cable isn't a problem. How small can we get the launcher?

Firing a 200-300g projectile, and allowing for energy to unravel the line? I'm not sure the muzzle velocity required, but I'd guess 30m/s or so would work? In which case, something comprable to a 40mm grenade (which is somewhat lighter and more areodynamic, but somewhat faster and longer range) seems reasonable. Not having fired an M203, I don't know for sure, but it seems recoil may be the practical limiting issue on launcher size?

Re: Batman Grappling Gun

Posted: Mon Feb 15, 2010 2:09 am UTC
by Cobramaster
You can still use a blank to fire the projectile and a 40mm is way more than you need to do so. Ideally you would use a .410 shotgun shell which has a manageable recoil and is much easier on the size issue.

Re: Batman Grappling Gun

Posted: Mon Feb 15, 2010 2:43 am UTC
by Cynical Idealist
PhoenixEnigma wrote:In which case, something comprable to a 40mm grenade (which is somewhat lighter and more areodynamic, but somewhat faster and longer range) seems reasonable.

Now, are you talking about the charge used to launch the grenade*, or the grenade itself?

Because your wording implies the latter, but that would be a little too much.


*From what I can tell with a quick trip to the wiki, a blank round or a regular rifle round for the muzzle-mounted grenades (using a regular round requires a specific grenade design to catch the bullet), so probably roughly the same charge for grenades that come with their own propellant.

Re: Batman Grappling Gun

Posted: Mon Feb 15, 2010 3:51 am UTC
by feedme
thoughtfully wrote:The bit that bugs me all the time is the nasty jerk at the end when the slack in your cable runs out. You need a really elastic cable if you want to stay attached to your arm!



Speaking from experience?


I guess the main factor is what's "portable". Do you want it on your belt...or to be able to sling over your back? I'd think that a spool of cable and some compressed gas could be made into a device to carry. Sadly I doubt it'd be slick like Batmans :(

Re: Batman Grappling Gun

Posted: Mon Feb 15, 2010 4:57 am UTC
by Cobramaster
You have to remember though Batman has a development budget that rivals the DoD and it gets spent on one guy.

Re: Batman Grappling Gun

Posted: Mon Feb 15, 2010 12:24 pm UTC
by Mr_Rose
Cobramaster wrote:You have to remember though Batman has a development budget that rivals the DoD and it gets spent on one guy.

In at least several cases his development budget was part supplied by the DoD; they just wound up not using the final product for whatever bureaucratic reason so he thought "waste not; want not" and ran off a few examples for private use.

Also, if the cable is too inelastic, the next best contrivance could be a mobile reel/motor assembly attached to (the rest of) the launcher via some sort of spring/dampening system to smooth out the bumps a little. Though this would add significant mass and bulk to the launcher, so elastic rope is still preferred.

Re: Batman Grappling Gun

Posted: Mon Feb 15, 2010 10:47 pm UTC
by breintje
I am wondering here if you couldn't use carbon nanotube material to replace another part of this assembly. The Hook. Would it be possible to create something similar to a gecko's footpad using such tubes? Since a single gecko can (ideally) support about 130 KG (!), according to wiki, it seems to me that using something like this would make your system a lot more versatile. You don't need anything for your hook to catch behind/onto, just a reasonably clean, non-teflon surface (A hook should ofcourse be included as well, in case of extremely wet or dirt-covered objects to climb).
As far as I know it should be possible to create a reasonably practical shooting system, but a decent rate of ascent would be hard to achieve, given the power needed to lift a person+kit of ~150 KG (1,5 KW / (m/s)). You need an engine with the power of a moped if you want to get up someplace before dying of old age, and that adds considerable bulk to your system.

Re: Batman Grappling Gun

Posted: Mon Feb 15, 2010 11:10 pm UTC
by Agent_Irons
The limiting technology is definitely not the cable or even the hook. The hardest part about this is the engine that lifts a human being and equipment, at speed. Ideally you should go zipping on up quite briskly. I'd like to ascend the 25m cable in about two seconds, if that's okay with everyone else. That's about 2 kw, or 4 kj, for a 150 kilo load. (From the department of meaningless units: 1 gram thermite.) That's kind of a lot of energy to fit into a small handheld weapon.

One possibility is prewound springs, which could dump a lot of energy into the cable quickly. The spring can be rewound by onsuit batteries.

Re: Batman Grappling Gun

Posted: Tue Feb 16, 2010 1:38 am UTC
by rocketrat
Agent_Irons wrote:One possibility is prewound springs, which could dump a lot of energy into the cable quickly. The spring can be rewound by onsuit batteries.

Now that is a good idea. Then the slow, small but very high (low? can't remember) gear ratio electric motor could get it re set. Jamie's could go at about 1 m/s, even with a very small motor.

Also, for the cable to not need high tech materials, kevlar and gel spun polythene are two very effective materials. Off the top of my head, kevlar is about 5 times the tensile strength of steel. I'm not sure about GSP, but extremely thin lines of it can withstand incredible amounts of force. And unlike steel and probably carbon nanotubes, it can flatten when spooled to take up less space. Sorry for not doing the maths here.

Just so that we don't need Batman's budget.

Re: Batman Grappling Gun

Posted: Tue Feb 16, 2010 3:06 am UTC
by Meteorswarm
How are ultracapacitors coming these days? If a motor that small would work, they might be a tidy solution to the "short burst of energy" problem, and you could use them for elastic-simulating braking at the end.

Re: Batman Grappling Gun

Posted: Tue Feb 16, 2010 6:46 am UTC
by Tass
rocketrat wrote:
Agent_Irons wrote:One possibility is prewound springs, which could dump a lot of energy into the cable quickly. The spring can be rewound by onsuit batteries.

Now that is a good idea. Then the slow, small but very high (low? can't remember) gear ratio electric motor could get it re set. Jamie's could go at about 1 m/s, even with a very small motor.


You need a big and powerful spring to store that muck energy.

Re: Batman Grappling Gun

Posted: Sun Sep 19, 2010 6:05 am UTC
by Batkram13
Wow, just remembered this. I'm glad the good people of the xkcd forums put so much thought into things.
One day, when I'm not in college and I have the necessary funding, I will be building this.