Introduction: Grappling Hook Launcher

About: Currently working on upgrading construction sites everywhere at REEKON Tools. Formlabs/Shaper Tools/MIT Alumni

As surprising as it is, there really is no where on the internet where I found any decent instructions on how to make a grappling hook gun. Figuring it would not be that hard to make, I decided to design and make one myself.  After running into  many problems, obstacles, and a few prototypes, I think I finally have a really solid version that definitely will impress all who use/see/build it.  Naturally there are sure to be plenty of upgrades and other ways to accomplish what I did but I will share the parts and methods I used to make this particular launcher.    
  Although I call it a grappling hook launcher, it is basically a souped up version of any pneumatic gun.  I took the best aspects of many different spud guns to make one of the best possible systems doing my best to avert creating any weak spots and not using any dangerous PVC (which shatters when over pressured and does not work well in the cold).  This system is designed to be robust and efficient in every aspect of its construction.  It is not hard to build and the most trouble anyone would have is gathering all the materials needed.
       I tried my best to used parts locally avaliable (Home Depot, Lowes, etc) but a few i needed to order online. Feel free to ask me any questions you may have. 
   For everyones information, if you are really that concerned about why I didn't film myself climbing the rope,  you are missing the purpose of the video, to show you how it works.  The hook and rope combined for my gun weight 2lbs 2.1oz for anyone concerned that this device isnt practical.  Also, I launched the hook at 150 psi and you could go much higher to achieve greater heights.  
     A little background on myself; I am current a Mechanical Engineering Student at the Massachusetts Institute of Technology  (MIT) and have been building things for 14 years.  My personal blog has most of my creations (some of them made by following Instructables).  Enjoy.  

Step 1: Parts and Materials

My advice to you is you read through the entire instrutable first before beginning to build or obtain parts to make sure I have everything correct or if you see any modifications you would like to make.  Please do not hesitate to contact me with any comments/questions/concerns you may have.  

Parts Needed for Launcher Assembly

-Dry Chemical Fire Extinguisher
-N-Strike Raider Rapid Fire CS 35 Nerf Gun
-Black Spray Paint
-Air Tool 3/8" Hose 
-20 oz CO2 Canister
-Paintball Coil Hose
-1.5 feet 3/4" Copper pipe
-8 inch tie downs
-Blow Gun
-(3) 6" Hose Clamps
-(4) Adjustable 5/8" Hose Clamps
-QEV Valve
-Pressure Gauge (mine had 1/8" threads on it)
-Teflon Tape
-J-B Cold Weld

Brass Fittings
-3/4" garden hose to NPT thread adapter
-3/4" to 3/8" Reducer 
-3/8" Close Nipple
-3/8" to 1/4" Reducer
-(4) 1/4" Close Nipple
-1/4" Cross
-1/4" Tee
-1/4" Check Valve
-175 psi Safety Valve
-(4) 90 Degree Elbows (male x female)
-(2) 1/4"x1/8" Reducing Bushing
-(4) 1/4" thread  x3/8" barb Hose Barbs

14mm, 15mm, 16mm, 18mm
2 Adjustable wrenches
Copper Pipe Cutter (hack saw would be fine too)
Phillips and Flat head Screwdriver
Drill with set of bits
Dremel with bits (Sanding, a few grinding and the cutoff wheel)
Exacto Knife to cut hose
Propane Torch (Soldering copper pipes)

Some other basic tools that I'm sure you have 

Step 2: Plans

I've never been a big user of any CAD program so hopefully these drawings will suffice. This is just to give you an overview of the design which was the second hardest part next to obtaining the materials.  Designing a robust launching system took several tries and eventually I got to this one which seemed pretty solid.  Each step I tried to include a drawing about what we are assembling to make it as easy as possible to follow. All the joints are Teflon taped. 
      So the concept behind this is simple, create a safe, strong and powerful launcher.  Originally (as seen in the photo) I built the device out of SCH-80 PVC but I always have the thought of it exploding in little shrapnel too scary and ABS (which just splinters) was too hard to find.  Also, PVC doesn't fair very well in the cold.  Which also leads to the air source, CO2 (which all the paintballers know can get very cold).  So instead in the second version, I made everything I could stronger (a lot of metal).  You could get away with building this out of PVC but I didn't want to take the risk of anything exploding if i went up in the 150-200psi range (although my current saftey blow off valve is rated at 175 psi).  (Message me personally if you want the plans for this gun as it is much easier to make if your looking for a quick project).  
    The final version begins with the CO2 coming from a paintball cylinder.  It enters the gun through a check valve (to ensure it does not come out once it enters the tank) and then a Quick Exhaust Valve (QEV).  The tank has a gauge on it to show pressure, a blow off safety valve which releases air over 175psi to ensure nothing bursts (although the system can probably handle up to 300psi).  When the air is fully charged, a blow gun is used to change the direction of flow in the valve to allow the air in the tank to exit through the barrel and hence launching the projectile.  

Step 3: Tank

The first thing I built on the final version is the storage tank.  As you may have guessed, it is a fire extinguisher.  However, to this date, I could not find ANY fitting that screwed into the mouth of the tank.  I wound up using a 3/4" adapter (NH to NPT thread) and cold welded it into place.  The rating on the weld is over 6000psi so in theory its the strongest section of any part of the tank.  

First discharge the fire extinguisher wherever you want (fun part).  Next, place the head of the extinguisher in a vice, clamp and twist bottle to the left to loosen it from the base (make sure you already discharged tank before this).  Once the nozzle  section  is  separated from the tank, all you need is the rubber gasket at the top of the stem.  Carefully remove it with some needle nose pliers and save it, the rest of the assembly can be discarded as we will not need it for the rest of out project.  

Next, take the gasket we previously removed and fit in on the NH side of the adapter (this side will have about 3 threads spaced farther apart) and slide it as high as you can get it. You are now ready to cold weld the tank and adapter together. Follow the directions of the cold weld and mix it together.  Apply generously to the NH sides of the threads and insert into tank.  Let tank dry upside down so cold weld goops up at the bottom (following gravity) of the seal which which we want.  Place something heavy on top and leave for 24 hours to set.  

Put the other parts on only after the weld has completely dried.  I would keep a wrench on the 3/4" adapter so you dont put the torque on the weld itself when you put on the other fittings.  

Step 4: CO2 Tank

I got my CO2 tank (20oz) from Lowes.  You can probably find one cheeper online.  There is nothing really hard in this step.  All I bought was the tank and a CO2 paintabll coil hose.  The coil hose had a quick connect included with it which was great.  I've included a link of where to buy this set up as it makes things a lot easier in future steps (although you could get away without it).  Once you have both, simply connect the regulator to the tank but dont screw down the top nozzle as we dont need any co2 to come out yet.  At the end with the quick connect on it, unscrew the black 3/8" fitting (meant for paintball guns) as we do not need this, it is round with a gasket on it.  The 1/8" silver piece of the quick connect that is exposed once we remove this black piece will work just as well.  

Step 5: Barrel

The barrel is made completely out of copper.  Here, you need to have some knowledge of sweating pipes (easy to learn if not).  Once you have connected all the copper sections, connect the the 3/8" to 1/4" reducer.  Although I have the hose barb pictured next, don't do that. Put a 90 degree elbow instead and leave the barrel like that.  This will make it inserting it into the cannon easier later.  So the only change from the picture is the 90 degree elbow instead of the hose barb and hose.

Step 6: Blow Gun

Another pretty straight forward step.  Put the two hose barbs in the hose, clamp down, screw in blowgun on one end.  You may have to cut the hose to the right length later on so it may be wise not to insert the second barb until you know how long the hose will be.  

Step 7: Connecting Everything on the Tank

Now we attach all the fittings to the tank assembly we made in the previous step.  Make sure to add the check valve, I forgot to put it in the drawing.  Do not connect the barrel, blow valve or co2 yet, just make the tank assembly as seen in the first picture (I moved the check valve to right after the tee in my final version but it isn't that important.)  Use a reducing bushing to connect the cross to the gauge.  

Step 8: Connecting Entire System

If you plan on assembling this gun and not attaching it to a nerf gun as I have, this is your last step. Feel free to make whatever you want out of it.  Its pretty easy to change barrel sizes and all sorts of modifications.  Continue onward to place the assembly in the gun (still do not attach the barrel, blowgun, or co2 yet.)

Step 9: Nerf Gun Disassembly

This is the nerf gun I used.  Pretty much everything gets ripped out.  Sorry But I didn't take any pictures of this step.  Basically you want to unscrew the whole thing and clear out any loose parts.  Next, using a dremel and your own judgement, dremel out what you think will get in the way of the cannon barrel.  You are essentially creating a tunnel in the nerf gun for the barrel to slip into.  Once you have all of it Dremeled out and have ensured, by testing, that the barrel fits, paint it whatever color you like and let dry.  I made two additional holes. One on the very end for a hose clamp and one for the pipe from the barrel to come out but do this after you have painted and screwed it back together so you know where to do it.  

Step 10: Securing Tank and Stem to Frame

Using the hose clamps, secure down the tank to the frame of the gun.  Cut a small piece of 1/2" PVC to support the cross (or whatever else you have handy.  You will need to make a slot for the clamp at this section. 

Step 11: Attaching Blow Gun to Frame

Screw in end of blow gun assembly and using the screw tie downs, secure the blow gun to the grip of the gun.  You may need to cut the hose first to be the correct length.  

Step 12: Inserting Barrel

In this step, we inset the barrel into the frame.  If you dremeled the gun out correctly, the barrel should slide back to about the back grip without a problem.  If you haven't already, see how far the barrel goes back and drill a hole for the air to get to the barrel.  The 90 degree elbow on the barrel should be aligned with the hole you made.  Insert a 1/4"x1.5" nipple into the elbow attached to the barrel.  put another elbow on the other end (exposed) of the nipple.  Connect the QEV valve to the 90 bend with a section of air hose (I assume you can make a length of hose by now.  

Step 13: Grappling Hook

You will have to forgive me but my real grappling hook got lost in the woods on a test fire.  Here is my imporvised replacement that I used in the video to demonstrate the concept. If you have a real grappling hook, it will work the same way depending how heavy it is. A big factor in determining how far it goes is how it fits in the barrel.  This may require the use of rubber gaskets and some light oil and some wadding.  Play around until you find something that works.  You have a very powerful air cannon at your hands so this is the only limiting factor at this point.   The rope needs to deploy smoothly so coil it up nicely.  You could add some kind of pole to go on the gun to allow a smooth deployment but I have just been laying it on the ground.   

Step 14: Finish and Fire!

Congratulations, you have finished the gun!  When charging with CO2, be very careful not to overcharge.  The safety valve should prevent pressure from building up past 175 degrees but I make no guarantees.  Put very little at a time.  Screw the release valve very carefully and slowly and always be ready to turn it to the left (off). I usually charge mine to about 120psi.  Don't be stupid though.  Be careful with it, don't shoot anybody or anything with it and never point the barrel at anything you don't want to shoot.  I claim no responsibility for people being foolish while using it. 

Step 15: Modifications

Here I will post modifications that I make to it, or ones that user's make and post pictures of here.  I'll only post ones that are completed and tested as many ideas may seem good on paper but may prove difficult/impractical to build.  

Modification 1
A simple device made out of PVC to use a tire valve (air pump) to connect to the system if you do not want to use CO2.  I'm not sure how it will work with a check valve but it can be used in whatever air cannon project you want.

Modification 2
Another crude grappling hook.  It probably does not support weight but it looks pretty cool.  I used 1/2" copper with endcaps on each side. On one side, I drilled a hole and added the hooks.  I coated the endcaps with camera film to make them smoother when it exits the barrel.

Modification 3
I added the CO2 tank to the gun by just strapping it down with the hose clamps and a towel underneath so I did not scratch the tank. There are probably many ways to affix the tank so keep the ideas coming.  

Modification 4
I threw on a shoulder strap so one could carry it while keeping their hands free.  I do not have any pictures of it but basically I just took one off of a laptop bag and then attached it using, yet again, more hose clamps (strong zip ties may work as well).