Reliable Water Rocket Launcher

Water rockets are a great way to have fun and provide educational opportunities. We designed a water rocket launcher for our 4H Club since several of our members were doing Water Rockets for a project. The idea behind this launcher was to make it out of easily obtainable parts and make it so it can be assembled by the youth of our club with minimal adult assistance. It was designed to be reliable and robust. We have used this design and it has launched hundreds of rockets. It holds up well, it is compact and easy to use. The following Instructable will lead you through the process to make one of these launchers. There are a lot of pictures and details. Do not be discouraged by the number of steps! Remember to use good judgement and common sense. Have fun and enjoy.

Here is a list of the items you will need to build this launcher. These pictures only represent a few of the total items As we go through the building process each item will be identified throughout the process.

1- Heavy Duty Plastic Electrical Box, not the standard plastic boxes! I get one from Lowes. The brand is Carion #BH122A. It is a 2 x 4 x 3 1/2 deep box

2- 16 penny nails (Sinkers)

2- 1 1/2" long Wood Screws

1- 3/16 eye screw with a 1/2" eye. It should have about 1" of threads

1- 1/2 NPT to 1/8 NPT Bushing reducer (Galvanized or brass)

1- Air fitting for portable air tank (Schrader Valve) You can get them from an auto parts store

1- 1/4 Nylon Tubing compression to 1/8 Male NPT Fitting

1- 1/4 Nylon Tubing compression to 1/8 female NPT Fitting

1- 5/8 ID x 7/8 OD Buna O-Ring

15' of 1/4 OD Ploy Tubing

20' of 3/16 diameter Nylon String

16 Inches of 1/2 CPVC pipe

1- 1/2" CPVC Winged Elbow

1- 1/2 CPVC Coupling

1- 3/8 slice of 3/4" PVC Pipe

1- 1 x 6 x 12" long Board

CPVC Glue

5 Minute Epoxy

Teflon Tape

Tools

Drill, Drill bits, 1 1/8 Drill Bit or hole saw, Hacksaw, Bandsaw (Optional), tape measure, square, sharpie marker, assorted files, screwdriver,wrenches

Remove the nails from the Electrical box.(Fig 1)

Mark a center line down the middle of each side of the box. (Fig 2) It is important to measure this accurately because we will reference our dimensions off of it.

I use a square and lock it to 3 1/8" inches and mark a line 3 1/8" from the bottom of the box.(Fig 3)

Mark this line about 1 inch long (Fig 4) on each side of the center line. Do this on both sides of the box.

Fig 5 shows the completed line at 3 1/8 from the bottom.

On one side, make a mark on the center line 1" from the bottom and 2" from the bottom. (Fig 6)

On the line you drew at 3 1/8 from the bottom, measure from the center line 5/8" and make a mark on each side of the center line. (Fig 7)

Fig 8 and fig 9 show each side of the completed, marked box.

Drill a 1/8 pilot hole at each of the locations you marked on the box. There should be 6 holes total

In this step, the box must be firmly clamped in place. I use a 1 1/8" spade drill to drill out the holes on the at the 1" and 2" mark in the center line. A hole saw also works well. When using the spade drill, drill each hole a little at a time. Be careful and use light pressure. When finished the holes may be a bit rough looking. Use a coarse file to file the sides straight to make a nice looking slot. Also smooth any rough edges.

The next step is to drill the holes in upper portion of the box. These are the pilot holes on the line drawn 3 1/8" above the bottom of the box. Use an 11/64 drill bit and drill from one side of the box and then drill to the other side. This will help keep the holes aligned. Clean any rough edges from the drilling process with a file.

To complete the Launch holder, draw a center line on the bottom of the plastic electrical box. Center the 1/2 CPVC Winged elbow on the box and mark each mounting hole on the winged elbow. Pilot drill each hole at 1/8" and then drill them out to 3/16".

I use a small band saw to cut the CPVC and PCV Pipe. After cutting the pipe, deburr all rough edges.

Cut the 1/2 CPVC Pipe to the following lengths.

1 at 8" (Pull Handle)

1 at 3" (Launch Tube)

1 at 2 1/4" (Latching Yoke)

1 at 1" (Joiner Tube)

2 at 1/2" (Base supports)

Cut one piece of 3/4 PVC Pipe to 3/8" for a spacer ring

This project can be made with hand tools, and one very important thing needed is to drill a hole in the CPVC pipe that is centered in the diameter of the tube. Often times if you drill by hand from one side the hole will be off center. What this template allows you to do is to mark one side and then the opposite side and insures the hole will be centered in the diameter of the tube.

Lay the pipe on a flat surface and lay a pencil tightly against it. Draw with a Sharpie, a line along the tube using the pencil as a straight edge. (Fig 1)

Wrap a strip of paper about 1" wide around the tube and overlap the starting point. (Fig 2)

Make a line on the paper where it overlaps the starting point. (Fig 3)

Cut off the Excess (Fig 4)

Fold the paper into quarter sections (Fig 5)

Mark each fold (Fig 6)

Wrap the template around the tube and put a piece of tape on the paper template. The template should slide on the tube and you should be able to slide it on and off. (Fig 7)

We will start with an easy piece. Take the 8" piece of the CPVC Pipe and make a line about 2" long int the center of the tube on one side using the pencil as a guide. (Fig 1)

Slide your template over the tube and line up the taped start / end point of the template with your line (Fig 2)

Turn the tube 180 degrees to the line on the template across from the start stop line. Make a mark extending from each end of the template, lining them up with the line drawn on the template. (Fig 3)

Lay the tube on a flat surface and line the marks you just made, using a pencil as a straightedge. Draw a 2" line connecting these marks. (Fig 4 and 5) You now have two lines on the CPVC tube directly across from each other.

Mark 4" on each line you drew. Make sure to measure from the same end for both marks in case your tube is not exactly 8" long. (Fig 6)

I generally drill a 1/8 pilot hole in each of the marks. (Fig 7 and 8) Once the pilot hole is drilled, enlarge the hole to 3/16 an you can drill through both holes from the same side (Fig 9)

Take the 2 1/4 \" piece of CPVC Pipe and slide on the marking template. We are going to make 4 lines on this pipe so make small marks on the pipe extending from the template lines.(Fig 1)

Mark 4 lines using a pencil as a guide and your marks. To make things easier, I made one set of lines Red and the other set black. A set are the lines that are across from each other on the tube. So it was red, back, red, black. (Fig 2)

I made identical marks on the other black line making sure to use the same end for my reference. One line is 1/2" from the end and the other line is 1 3/4" away from the same end. You can see from the picture I set the tape measure using 3" as the zero or starting point. This is because the end of my tape is too beat up to read it accurately, so I pick a good starting point on the tape to measure with. (Fig 3)

On the red line make a single mark 1 1/8" from the end (Fig 4)

Drill a 1/8 pilot hole at each mark. Do not hold this in your hand. Clamp it to the table or use a vice to hold it. (Fig 5)

Drill the holes out to 3/16 (Fig 6)

All holes are drilled (Fig 7)

Take two 16 penny nails. Do not use the nails that you pulled out of the box because they are thinner than a 16 penny sinker.

Use a file to blunt the ends of the nail. When the nails are blunt, put them through the hole in the launch tube and slide them into the holes in the electrical box. Everything should line up smoothly. Put some electrical tape over the heads of the nails.

Take a 3/4 " square of electrical tape, poke a small hole in it and slide one over each nail. Take tape and seal one end of the tube and wrap tape around the center of the tube to seal the hole drilled in the center. Slide the yoke assembly back into the electrical box with the open end up. Make sure it slides in and out freely. We are going to fill this with epoxy to strengthen the yoke assembly and keep the nails in place. The tape keeps the epoxy from leaking out. Make sure to use electrical tape because that releases easily from the epoxy.

I mix up enough 5 minute epoxy to fill the Yoke Assembly. You have to work quickly and make sure to mix up enough! Pour the epoxy in the open end of the tube. You may need to take a wire to poke in the epoxy mix to make sure there are not any huge bubbles trapped. When the epoxy is dry, remove the tape. Then re-drill the 3/16 hole in the middle of the tube.

Cut a 1/2" CPVC coupling in half. I used a small band saw, but it can be done with a hacksaw.

After the coupling is cut, there will be a small ridge.

Use a round file to remove the ridge left inside the coupling.

Then roll up a piece of sandpaper to slightly enlarge the ID of each coupling half.

Then place a piece of sandpaper on a flat surface and smooth the cut from the bandsaw

Lay out the Components shown in Fig 1

I apply glue to the sockets and the tube. (Fig 2 and 3)

Glue the 1" tube to the Winged Elbow and the NPT to CPVC adapter. Make sure the tabs on the winged adapter tabs are orienated as shown in (Fig 4)

Glue the 3" launch tube to the other socket in the winged elbow and wipe off excessive glue (Fig 5)

PVC Glue dries and sets very quickly. You only have one chance to get it right so prepare well!

Slide one of the coupling halves - O ring supports on the launch tube. Make sure the smaller diameter of the coupling is towards the winged elbow. (Fig 1)

Pit a little PVC Glue on the tube below the coupling half and slide the coupling half until it meets the winged elbow. (Fig 2)

Make a mark 1/8" from the coupling you just slid on (Fig 3)

Slide the other coupling half - O ring support on the launch tube with the larger end towards the launch tube. Apply some glue (Fig 4) and CAREFULLY slide the coupling half down to the line (Fig 5)

I use a neck of a 2 liter bottle to check the fit. It should slide easily over the o ring supports. Fig 1 shows the bottle neck hanging up on the O ring supports.

Take a flat file and go around the perimeter of the o ring supports to smooth them and slightly reduce their diameter (Fig 2 and 3)

The bottle neck should freely slide over the o ring supports (Fig 4)

Be patient during this process. The o ring groove must be filed for the launch er to work properly. If it is too tight, it will be difficult to set the bottle, and if it is too loose, it will leak. To file the groove, use the side of a 1/8" file. File around the perimeter of the groove, removing all of the glue. You only want to remove 1/32 or so from the launch tube. (Fig 1 and 2)

Test fit the o ring. you should be able to easily roll it with your fingers it in the groove you filed. (Fig 3)

Test fit with an empty bottle. You may need to put a drop of soap on the o ring to help the bottle slide on. (Fig 4) I typically test a couple of bottles (Fig 5)

Remove the O ring you installed in the previous step. Take the 3/8 slice of 3/4 PVC Pipe and slide it over the end of the launch tube (Fig 1)

Push it down to the Winged elbow and use some glue to hold it in place. (Fig 2 and 3) The purpose of this is to act as a stop to keep the bottle from sliding down to far.

Reinstall the o ring (Fig 4)

In the Launch Tube Assembly, thread in a 1/2 to 1/8 bushing reducer. (Fig 1)

Thread the 1/4 tube to 1/8 Male NPT adapter into the bushing reducer. I use Teflon Tape on these fittings. (Fig 2)

Install one end of the 15' of 1/4" Poly tubing on the fitting. (Fig 3)

Assemble the Schrader valve onto the 1/4 tube to 1/4 Female NPT adapter (Fig 4)

Install the 1/4 Poly tubing on the Fitting Assembly (Fig 5)

The Launch Tube / Airline is complete (Fig 6)

Layout the 6 x 12" board according to the dimensions in the first picture. Drill a 1 1/8" hole 2 inches from one end in the center of the board. Drill a 1/8 hole at the opposite end of the board 1 inch from the end and 2 inches away from one of the sides. Screw the eye screw in this hole. Take the launch tube and center it on the line drawn across the board at the 5 1/2" line. Mark the holes of the winged elbow. Drill a 3/32 pilot hole at these marks. The final board layout should look like the last picture.

Place the Launch Holder Box on the board. Make sure the slot is facing away from the large hole in the board. Line it up with the pilot holes drilled in the board (Fig 1)

Put the 1/2" CPVC Spacers inside the box over the holes. These will space the Launch Tube assembly up the proper height. (Fig 2)

Place the Launch Tube Assembly over the spacers. (Fig 3)

Drop a screw in each hole and line the screws up with the pilot holes in the board (Fig 4)

Tighten the screws and tighten the launch tube on the spacers inside the Launch Holder Box. (Fig 5)

If the screws poke through the bottom of the board, take a file and file them flush with the board. (Fig 6)

Get the 20' of 3/16 nylon cord. Insert the nylon cord through the Yoke assembly. Make a knot about 16" from the end. (Fig 1)

Make another knot on the other side of the yoke and slide it so it traps the yoke in the cord (Fig 2)

Tie the short end of the cord (16" piece) to the eye screw. Tie it securely. (Fig 3)

I glue the knot on the eye screw to keep it from coming loose. I want to make sure that the launch yoke is securely retained after it is pulled out! (Fig 4)

At the other end of the nylon cord, feed it through the hole in the Launch Handle (Fig 5)

Tie a knot in the cord to secure the handle (Fig 6)

To use the launcher, drive a tent stake through the 1 1/8" hole. This secures the launcher when the yoke is pulled. You will have to put a little extra water in the water rocket because you will loose a little bit when you invert the rocket to put it onto the launcher. Fill the rocket about 1/2 full of water. Slide the bottle / rocket over the O ring and lock it in place with the yoke. Make sure not to pull the string before pressure is in the rocket! The yoke comes out very easily until there is a little pressure. We typically leave the string slack and do not pick up the launch handle until there is pressure in the rocket. Always have a countdown, and give the string a firm pull.

There is an assembly drawing from the original plans we developed for the 4H club. Hopefully these instructions are clear enough for you to build one.

Stay safe and have fun!

If you want to build a foam nose rocket that flies great, please look at my Noodle Nose Water Rocket Instructable. Thanks!