Compressed Air - Acorn Launcher

Make a powerful, air compressed acorn launcher.


A couple of years ago I designed a Hand-held Compressed Air Gun/Launcher. It was made to launch paper rockets and actually worked really well. You can check out the instructable here.

The idea behind the Hand-held Compressed Air Gun/Launcher was to use a sprinkler valve to release the compressed air which was stored in a chamber by a hand pump attached to the launcher. My first design was a little clumsy and there was too much re-working needed on the PVC piping.

Once of the things that I did discover was the launcher was fantastic at launching acorns! This inspired me to make the launcher better so I decided to go back to the drawing board and really make this something special.

This is a real dangerous weapon which makes it damn fun to use!  Saying that, if you do make one - be cool and don't hurt your fellow man or beast.

The following instructions will show you how you can make one of these bad boys.


check out the video below to see it in action:

Parts:
1. 15mm PVC pipe (aprox 400mm long) - barrel of the gun
2. 20mm female threaded / 20mm coupling 
3.  15mm coupling
4. 32 mm T pipe
5. 25mm coupling / 25mm threaded x 2
6. 32 mm PVC Pipe (aprox 700mm long) - handle and air chamber
7. 32 mm Cap
8.  20mm female  / 25mm male coupling
9. 25mm male threaded / 32mm coupling
10. 32mm coupling / 25mm Coupling
11. Plastic pump – small
12. Sprinkler valve
13. Toggle switch
14. Momentary switch
15. 2 x 9v battery holders
16. 2 x 9 v batteries
17. Pressure cement
18. Plumbers tape
19. Blue LED
19. Resistor (47K)

Tools:
1. Circular saw
2. Soldering iron
3. Solder
4. Wire cutters
5. Dremmel

Once you have all of the parts needed, the next steps are to plan the build. Lay out all of the parts needed the as below drawing shows. This way you will ensure that you add the right parts together! Once of the trickiest parts id the "T" section but I will go through this in more detail later.

This drawing is not too accurate anymore as it was something I did before the build.  It gives you a good idea how the thing works though so i have left it in.

The "T" section is very important. It will be your handle as well as store all of the batteries, wires and switches. The first thing you need to do though is to add a piece of 25mm pipe through the middle

Steps:

1. Grab your 32mm "T" section

2. Cut a 150mm piece of 25mm pipe.  This piece of pipe will be going through the middle of the T section.


3. Glue one of the ends of the 25mm pipe into one of the 20mm female threaded / 20mm coupling. The threaded section should be on the outside.

NOTE - Before gluing - make sure that the piece of 25mm pipe is flush with the other end of the T Section.  If it is short then you will need a larger piece of pipe.  If it is longer, measure it flush with the T pipe and cut

4. Push the 25mm pipe through the "T" section and glue the coupling into the T section.

5. On the other end of the "T" section add some glue to the 25mm pipe and push on the other 22mm female threaded / 25mm coupling.

There is some modification that you need to do to the valve.  This is not totally necessary but does help with the wiring later (plus it also looks better)

Steps.

1. Un-screw the 4 screws holding the casing together.

2.  Add some plumbers tape to the end which will be going into the air chamber.  Screw on the 20mm female  / 25mm male coupling.

3. Turn the bottom section with the wires 90 degrees so they are in-line with the 2 male threaded ends.  The wires should be facing the opposite way to the arrow on top of the valve.

4. Screw the valve back together.

The next steps involve adding the valve and preparing the other end of the T section for the air chamber


1. Add some plumbers tape to the end of the male thread on the pump section and screw into one end of the T section.

NOTE: Initially I was just going to have a 25mm Barrel.  after some testing i found that this would be too small so i changed to a 32mm barrel.  The best part to add into the T section would have been a male threaded 25mm / 32 mm coupling.  I didn't have one of these on hand so I improvised.  I have added this part into the parts list.

2. Next screw onto one end of the valve the "T" section the  female end the male threaded 25mm / 32 mm coupling making sure that plumbers tape is used.

Steps.

1. Cut a 200mm length of 32mm pipe

2. Glue on the 32mm / 32mm male screw coupling onto one end

Making the stock
1.  Cut a small piece of 32mm pipe and use this to join-up the 2 curved 32mm coupling pieces

2.  add another small piece of 32mm pipe to the end of the curved 32mm coupling.  This should stick out about 40mm.

3.  Glue all pieces together

4.  Lastly, glue the stock to the end of the 32mm air chamber.  

Steps.

1. Cut a 250mm piece of 15mm pipe.

2. Glue together the 15mm to 20mm coupling inon the 20mm female threaded / 20mm coupling to one end of the 15mm pipe.

3. Screw into the other end of the valve, making sure you use plumbers tape.

To power the launcher, you need to fill the air chamber with air.  To be able to do this you need to add a valve to the launcher.

Steps.

1. First drill a hole in the end of the 32mm cap large enough to hold the valve in place tightly.

2. Add a good lot of hot glue to the inside of the cap to secure the valve into place.

3. Glue onto the end of the stock.

4. Next drill a hole in the air chamber where you want the PSI gauge to go.  You want it out of the way but easily viewed.

5. Use a tap and create a thread for the gauge to go into.  Make sure you add some plumbers
tape to the thread on the gauge to ensure a air tight fit.

I decided not to go with using a pump as I wanted an automatic system to pump up the gun.  I have left this here in case someone else wants to use a hand pump instead of an electric one.  There are some images of one of these that I previously made at the end of this Instructable.

Steps:

It's time to add the pump.  Make sure you don't glue the coupling to the air chamber first, as you need to add glue...you'll see what I'm taking about in a minute.

1.  Gather up the pump and 32mm / 25mm coupling

1. The pump that I used was slightly too large to go into the coupling end. What I did and you will probably need to do is use a dremmel to enlarge the hole. I used a round sanding bit and make the hole taper in. It's important to do this so the glue will stick to the pump. Once you have the hole large enough and the pump is a nice, tight fit, add some glue and stick to the coupling.

**gluing the pump is very critical and is probably the place where you might get a leak** 

2.  Next, add some silicon to the inside of the coupling to ensure that it is air tight.  Also add some silicon to the outside You could also use hot glue if you wanted.

3. Once all the glue and silicon is dry, , glue on the 32mm / 25mm coupling to the air chamber

Steps.

1.  Drill a hole at the top of the handle section of the “T” section and another one underneath it.  The top one will be used for the LED and the bottom for the safety toggle switch.  Obviously make sure that holes are bigger enough to accommodate each item.

2. Drill a hole on the opposite side large enough to allow both wires from the sprinkler valve to go through.

3. Drill another hole on the handle but this one is to go on the front where your trigger finger sits.  This is where the momentary switch will go.

4. Next solder all of the electronics together.  It’s a lot easier if this is done first before you put all of the bits into the “T” section.  The only thing that you will have to do is to make sure that the wires from the sprinkler valve are through the hole in the “T” section first before soldering onto the other bits.

5. The diagram attached will help you work out how each part is soldered together.

6.  Hot glue into place the LED.

7.  Next attach the toggle switch and push switch.

8.  Solder on the wires from the valve to the sections indicated in the drawing below.

9.  Attach the batteries and test.

Steps:

1.  cut a piece of 32mm pipe.  150mm should be fine.

2.  Next modify the pipe on one end as shown.  Remember this is going to be your handle so it needs to slip into the bottom of the T section.  You have to make a couple of mods to allow the switches to slide through the pipe.

3.  Thread the wires and batteries through the pipe and glue into place.

4.  Push on the 32mm cap.

Now that you have your finished product It’s time to give it a lick of paint.  When painting PVC, it’s important to choose the right paint.  I went with the one below which also adheres to plastic.

Steps.

1.  Cover all of the parts that you don't want to paint.

2.  Hang-up the gun with some wire outside and spray away.

3.  Repeat coats if necessary 

4.  If you need to touch-up any sections which might have missed being painted, use a black, permanent marker.

There are many ways to add a sight to your gun.  Initially I was just going to stick a laser onto the gun and be done with it but then I had a look around my shed and found an an old, aluminium cowling from a head lamp.  I thought that this would make a perfect cap to the end of the barrel and would hold a screw in place for the sight.

Steps:

1,  The main thing with making a sight is to have something sticking-up at the end with which to aim with.  I used a small screw.

2.  Next you need to line the screw on the barrel up with the stock.  I used a piece of steel that I had with a hole in it and modified it to make it into a "V"

3.  You need to be able to move the "V" left and right to calibrate the targeting system. To do this I used a cable tie to hold the "V" into place.  This enabled me to turn it if necessary.

So that's it - you should have a damn fine weapon which fires acorns (or whatever else fits into it!) at some serious speed.  

This isn't a toy, so be careful kiddies and don't go firing it at each other.


Things I Learnt.

• Adding a pump to the end is really a good way to make this portable.  I have done this on other versions (check out the below photos) and they really work well.  The one drawback is your arm starts to get sore due to all of the pumping you have to do!  Also, you have to modify the actual PVC coupling to allow the pump to fit correctly and this becomes a real weak point in the launcher.  I had to add a heap of glue just to make sure it didn't shoot out at me!  The pump that I used also broke when I was doing the finishing touches which made it leak.  The best pumps to use are ones that inflate when you are both pushing and pulling the handle.
• I wanted to make this one have an electric pump which at a push of a button would fill the chamber.  Unfortunately, all my experiments came to naught.  The think is, you need some serious amperage to get enough pressure into the chamber and I just couldn't find a battery small enough to be portable.  Plus you have to carry an electric pump as well.  I am still looking into options and if i come across one I'll post it on here.
• With the first launcher I made which can be found here  ible' member ilpug gave me some suggestions on how I could improve the launcher.  Here is what he suggested:

-replace the ball pump with a small bike pump. Bike pumps have a higher pressure rating and are much tougher. They have a much more reliable one-way valve to prevent damage to the pump. Also, if possible, make the pump removable so if it breaks the entire gun isn't junk.
-Add a pressure gauge. Also, some bike pumps have one attached, so you could just use a pump with a gauge attached. This lets you always pump to a known pressure, regardless of temperature, to give you more consistent accuracy.
- I would make the barrel on a screw attachment so you can swap out barrels for different sizes, lengths, kinds of ammunition.
-Give it a stock or shoulder rest.
-make smaller, denser ammo, i suggest taking your rubber corks and putting an eye screw in one end, then tying a few bits of string to the eye screw to act as a tail to improve accuracy. Try cutting pieces of dowel into rounds and firing those for more impact power.
-make a breech-loading barrel, so you can load ammunition into the back without having to ram it down the barrel. You could also hack a nerf gun magazine system into the gun to fire darts.

All these are great ideas and I managed to incorporate a lot of them into this build.  

• The ammo I used is seasonal!  not really the greatest idea but it is free and they fire amazingly well.  If anyone has any other ideas for ammo, then please let me know.  In Australia Paint ball guns are illegal, although we can buy the actual paint balls.  I think I will get some of these and give them a try. I have also used small globes I found at the car wreckers.  These are deadly and also work a treat.  I would suspect that anything that fits snugly into the barrel would work just fine.