Quick Change Electronic 2 Litre Water Rocket Launcher




Introduction: Quick Change Electronic 2 Litre Water Rocket Launcher

OK so I have been lurking here on the site for some time and this is my first instructable. This was my second launcher the first was a modification of the one from  "This Old House."  I used a ball valve instead of the complicated zip tie design. No offense to that design, but it just seems a bit much and possibly prone to failure. I admit freely that this design is not the cheapest but it fit my needs for form and function.

Please remember that the act of pressurizing a vessel can be dangerous and even deadly. If you are not sure if something is correct or doubt your construction in anyway, DO NOT USE IT.

This instructable is for information only and I assume no responsibility for your actions after reading it.

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Step 1: The Basic Design

I wanted the launcher to look spacey,  I liked the way rockets looked from the early space program, so I built the unit  vertical and tall instead of horizontal and close to the ground.

I wanted to be able to use both a bike pump and an compressor or compressed tank so there is both a schrader valve and a compressor fitting.

I wanted it to be electrically controlled, so I used a sprinkler valve and and string of 3 9v batteries to power the valve.

The most important thing I wanted to change was how the bottles were placed on the launcher, because they are 1/4 full of water  other designs required the entire unit to be tilted down  for loading. I thought this was dangerous since it allowed the possibility for an accidental horizontal launch if the system was primed. So I made a sort of quick change system that allows for much faster cycling and more fun per minute!!!

Step 2: The Parts

All of these parts were purchased from Lowes and Radio Shack. The only exception was the tire inflator--I already had that, but I got it from Harbor Frieght.

Tools Used

PVC Preparation
Chop Saw (you could use a hack saw)
Drill Press(You could use a Hand Drill or a Brace if your old school)
De-Burring Tool( You could use sandpaper or a utility knife--be careful)
1/2 Drill Bit for Schrader Valve
7/32 Drill For Tap
1/4 NPT Tap (If you don't have a tap, the PVC is soft enough to just use the part as the tap but take your time.)
One Sheet of 100 Grit Sandpaper
Channel Locks(You might be able to use pliers)

PVC Construction

Framing Square to ensure the base is plumb to the ground( in a pinch anything with a 90 degree angle could work, even a hard bound book)
PVC  Glue
Teflon Tape

Electrical Control Box
Phillips Screw Driver
Wire Strippers
Hot Glue Gun( You could use any adhesive, its just so much easier with Hot Glue)
Needle nose Pliers

Brass Plumbing
1/4 wrench
Teflon Tape


Parts PVC
X 3   2" T
x 4   2" Cap
x1    2" 45 Deg Coupler
x1    2" Coupler
x1    2" to 1" Reducer
x1    1" to 3/4 female threaded
x2    1" to 1" Female Threaded Coupler
x1 1" Sprinkler Valve In-Line ( I used Orbit because it was the cheapest)
Paint bucket Lid (this is optional, but I liked the way it looked and diverts the blast water more uniformly.)

Plumbing Parts
1 Schrader Valve( This is if you ever want to use a Bike pump)
25' 1/4 Inch Air Hose
1/4"   115 PSI Brass Relief valve( This is just for safety, since i was using it around kids.)
1/4" Brass T
1/4" Air hose Male Bib
1/4" Air Hose Female
1/4'" Pressure Gauge(my tire filler had one already)

Electrical Parts
25' Phone Cord
2 Surface Mount phone jacks
3 9v Snap Connectors
3 9V Battery Holders
1 Medium Project Case
3 9v Batteries
1 Switch(I chose a rocker with the safety cover for effect)

Step 3: The PVC CONSTRUCTION--The Base--Dry Work

Begin by collecting the parts for the base.

4 2" End Caps
3 2" Tees
1 45 Degree Coupler

approx 2' of 2" Pipe

You will need to cut  7 pieces from the 2" pipe . I cut them about 2". This made the joints I would be making flush. (In hindsite, I would recommend doubling them to 4-6 inches to give a more stable base--sometimes kids get excited and pull on the launcher wire and it can tip the launcher over)

I cut them using a chop saw with a wood block set to the correct measurement.

Once I had all of them cut I smoothed and squared the edges by rubbing each end in a circular motion on a piece if 220 grit sand paper on a flat surface.

Make a hole in the center of one of the end caps using the 1/2" bit .

Clean up the hole.

Push the capped end of the schrader valve through the inside of the end cap and pull through using vice grips or pliers. It is set when it looks even.

Using the 7/32 Drill (3/16 will work in a pinch) drill a hole in the center of a second end cap.

Tap this hole using the 1/4 inch NPT tap . If you don't have a tap you can work the brass fitting in slowly.)

Use Teflon tape to cover the the threads of the 1/4" Air hose Male Bib . Apply counter-clockwise.

Attach bib.

Step 4: PVC Construction--The Base--Wet Assembly

I recommend wearing gloves, having a rag nearby and doing the gluing over cardboard or newspaper. YOU WILL DRIP!!!!

What we are going to do is mate the small sections of 2" pipe to  two of the 2" Tees creating a left and right side.

Be sure to apply a light film of the cement to both parts to be mated and be sure to seat the male part into the female part. IE push till it wont go any further.

Do this for two of the tees.

You should have 1 short section of pipe left over.  Glue this into the 45 degree coupler, it doesn't matter which end.

Glue the Brass Coupler cap to the 45 degree fitting. The purpose of this is to keep the fitting elevated when using the launcher.

Lay the tees so that the middles are facing each other.

Glue a 2" end cap to each sections "top."

Glue the "Schradered" cap to a bottom.

Glue the 45 degree couple to the other bottom. Be sure the 45 is angling up.

Now dry fit the last tee between the two you just built. NO GLUE AT THIS POINT!!!

Also dry fit a section of 2" pipe into the middle of this tee.

Using a square position the upright tube so that it is perpendicular to the ground.

Using a marker make a line across the tee and the ends that connect the sides pieces to the middle tee. This will allow you to line up these lines when the glue is on and have it dry straight and perpendicular.

Step 5: PVC Construction--Tower

Once the base has set you can begin to assemble the tower. Again READ THE WHOLE SECTION BEFORE YOU START!!!!

The first thing is to determine how high you want you launcher. I wanted the business end to be taller than my kids, so there was no accidental  discharges into a face. It is really up to you though I think a minimum of 24" of 2 inch pipe would be prudent. I actually just used the section that was left over from cutting the small bits from a 4' section.

Glue a section of 2" pipe into the base.

Glue a 2" coupler onto the top.

Glue in the 2" to 1" reducer.

Cut a 6" section of 1" pipe.(You can really make it any length that you find appealing.)

Glue in the piece of 1" pipe.

Attached the 1" threaded couplers to the sprinkler valve. (I used a pipe wrench to help.)


Glue coupled Sprinkler valve to tower in proper orientation.

Drill a hole if the center of the bucket lid to fit a 1" to 1/4" female coupler.
The lip of the coupler will seat against the lid's hole.

Glue this assemble to tower.

Step 6: Electric Control

I liked the idea of having a remote switch to launch. It looks cool and kids and adults like the flip up switch.

Tools I used:

Wire Cutters/Strippers
Chop Saw
Drill Press
Soldering Iron
Heat Gun
Hot Glue Gun

Items needed (all were purchased at Radio Shack):

1 Medium Project Box
2 Surface Mount Phone Jacks
1 25 foot Phone Cord
3 9 volt Batteries
3 9 volt Battery Holders
3 9 Volt Battery Leads
1 Grommet
    Heat Shrink Tubing


1 The phone jacks have 4 wires Red, Black, Yellow, and Green. I first just used the black and red but found that they wires were too small to run the current over the 25 feet so I doubled them up and shorted the base of one jack so it would fit in the project box. I did Red and Green being Positive and Yellow and Black as negative.

2 I found that it was best if the batteries were to one side of the box and the surface mount on the other. The switch which would be mounted to the top cover had to go over the surface mount area or it would not fit.

3 Use a hot glue gun to glue in the mounts. It is critical that the batter is flush to the bottom of the mount as you glue it it glue will come up through the hole in the middle and your battery wont seat flush later.

4 Drill a hole for the phone cord insuring that it was on the side of the box that would be facing away from me as I held it. I use a bit just slight bigger that the head of the cord by sight.

5 Push the grommet over the jack being careful not to break the the little lever.

6 Feed the cord through the hole in the box and then work the grommet into place

7 Drill the hole on the top of the box for the switch. Again I just eyeballed it, I think the switch actually told you what size bit to use.

Now for the REALLY Critical part, the wiring.

It really wasn't hard, it is just critical that the batteries be wired in series and not in parallel.
(I hope I dont have that terminology backwards.) What you need is to go from positive to negative on the batteries so you get them producing more than 9 volts. If you wire all the reds together and all the blacks you will get only 9 Volts, In series they should produce ~27v.

8 Put battery leads onto batteries and place batteries into holders. Be careful not to touch any of the wires together. Number the batteries or go clock wise or something just to keep them straight to yourself as you wire them.

9 Take the red wire from battery one and join it with the black wire from battery 2.

10 Take the red wire from Battery 2 and join it with the black wire from battery 3.

11 The black wire from battery 1 and the red wire from battery 3 are now your positive and negative.

12 Attach the black wire from battery 3 to the Flush Mount on the same terminal as the black and yellow.

13 Attach the red wire from battery on to the appropriate point on your switch, then run a wire from the other point on your switch to the same terminal as your red and green wire. Note I used a black wire to do this sorry if it confusing in the picture, I just had a scrap that worked.

I am not going to go into detail on how to solder or use heat tube there are better instuctables than I would do so look them up if your not sure.

14 Assemble the box.

15 Wire the other surface mount to the sprinkler valve. Remember to double up the wires Red and Green and Black and yellow. It does not matter which sprinkler wire goes where.

Step 7: The Charging System

1/4 wrenchs
Teflon Tape

25' 1/4 Inch Air Hose
1/4" 115 PSI Brass Relief valve( This is just for safety, since i was using it around kids.)
1/4" Brass T
1/4" Barrel Adapter
1/4" Air hose Male Bib
1/4" Air Hose Female
1/4'" Pressure Gauge(my tire filler had one already)

So this pretty straight forward. We are creating an hose that connects to the air compressor that will allow us to charge the unit. I set it up so that the control valve and gauge were at one end and the quick connect and pressure relief was at the other. This puts the filler at a safe distance from the unit. I used the relief valve because little kids( as well as big ones) can get excited and forget to let go of the filler handle.

Use Teflon Tape on all the fitting connections.

1 Remove the tire adapter from the air valve/pressure gauge.
2 Mate the air valve/pressure gauge to one end of the of the pressure hose using the 1/4" Barrel Adapter.
3 Attach the other end of the hose to the 1/4" Brass T. Attach it to one of the inline female ends.
4 Attach the pressure relief valve to the other female end.
5 Attach the the 1/4" Air Hose Female to the remaining fitting on the T

You now have the ability to safely charge your system! 

Step 8: The Quick Change

So most of the launcher designs I have seen require you to tip the launcher over to put on the bottle. I wanted to be able to have rockets watered and ready to go.

The quick change stick consists of:

1 length of 1/2 inch PVC (~12 inches long for 2 liters and 8 inches long for 16 oz water bottles)
1 1/2 to 1/2 slip connector
1 smaller length of 1/2 inch pipe ( ~4 inches long)
1 1/2 slip to 1/2 male threaded

Assemble them as in the picture. Again use care with the glue.

You are now ready to LAUNCH!!!!!

Step 9: The Fun

You can play with the amount of water you add to the bottles to get your maximum fun. I found just about to the bottom of the lable worked great. Also, really any more than 80 psi is just a waste, also this is about the limit of the sprinkler valve. I found that more than 80 sometimes locks it. Use your imagination. I had some left over PVC parts and made a quad launcher as well.  There are also a ton of actual rocket designs, there are even multiple stage units. Do some googleing.


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    7 Discussions


    8 years ago on Introduction

    Nice Job on this. I went out and got the parts and built it last night. I didn't see in the material list the length of 2 inch pipe to get but you can never have too much PVC pipe around for other projects. :-) I am going to try and add a servo into the mix with a release idea from this one. https://www.instructables.com/id/water-rocket-launcher/ > then I will have two buttons on the control pad. Air up and Arm. then fire.


    Reply 8 years ago on Introduction

    Awesome! Let me know how it works out.


    8 years ago on Step 8

    Can you hash out step 8 a little more so I can be sure I am getting it right? The girl's hands are covering how the soda bottle mates to the "quick change" assembly. I am making an assumption that it is a friction fit and triggering the sprinkler valve overcomes the friction and launches the bottle. But you know what they say when one "assume".


    Reply 8 years ago on Introduction

    Yes it is just a friction fit. Unlike a lot of other designs, the bottle is not pressurized prior to launching. I think this may cause a bit of loss of height, but the kids and adults don't seem to mind. They just want to "do it again, do it again!"

    The bottle spout will rest on the coupler.
    What we do is fill the bottle with water about to where the bottom of the label is, insert the "quick change", invert and screw into the launcher. A small amount of water will leak as you prepare to launch.


    8 years ago on Introduction

    This is an awesome first instructable. It's always fun when lurkers make their first contribution. Some constructive feedback: use a photo editor to tweak the white balance in your pics, and make sure your main image is super-awesome. Beyond that, this is an excellent instructable. Keep 'em coming.


    Reply 8 years ago on Introduction

    Thanks for commenting and the feedback, will do!


    8 years ago on Introduction

    22 views but no comments? I need some feedback people:)