How to Make a Water Bottle Rocket Launcher from PVC

This tutorial shows how to make a water bottle rocket launcher from 1/2" PVC pipe, a tubeless tire valve, zip ties, and a cut-up 2-liter bottle. You pressurize the rocket with a bike pump through the tire valve, and a pull string releases it from a safe distance. The video estimates the materials at about $20 or less from a hardware store and an auto parts store.

Brock Wiberg of the Utah State University 2012 Chimera Rocket Team presents videos 1 and 2. Video 1 covers the parts and tools. Video 2 is the build. The steps below follow it. When the launcher is done, build the rocket that flies from it.

Safety first#

Tools you need#

• Electric drill and 1/2" drill bit
• A small drill bit, about 1/8", for the firing collar
• Square, to keep the rail upright
• Scissors
• Lighter or matches
• Flathead screwdriver
• Ruler
• Permanent marker
• Pliers, needle nose or blunt nose
• Box cutter
• Duct tape
• PVC primer and cement. The video says the primer is optional, but it gives a better seal.
• Bike pump
• A rag and a scrap of 1/2" pipe are handy

Step 1: Seat the tire valve in an end cap#

The valve is what you pump air through, and it has to hold the pressure that launches the rocket.

1. Drill a 1/2" hole in the closed end of one end cap.
2. Push the valve stem through the hole from the inside of the cap to the outside.
3. Wrap a rag around the tip of the stem and, using pliers, pull the stem through. It may take some force.
4. Keep pulling until the small rim on the valve pops out. Pull a little more to check that the valve is firmly seated in the cap.

• 1/2" hole drilled in one end cap
• Valve pulled through and the rim popped out
• Valve feels firmly seated

Step 2: Cut the pipe#

Cut two of the three 2 ft pipes into 8" pieces, three from each, for six pieces in all. Leave the third pipe at the full 2 ft length. It is the launch rail.

The video does not show the cutting. A hardware store can cut pipe for you, or you can use a PVC cutter or a hacksaw.

• Six 8" pieces
• One whole 2 ft pipe

Step 3: Build the two T-sections#

This is the basic PVC joint you will use for the rest of the build, so it is worth knowing how it works before you start assembling your bottle rocket launcher.

1. Work outside. Brush a little primer on the end of the pipe and inside the fitting. It smells bad and can drip, so do not do it indoors.
2. Once the primer has dried, normally just a couple seconds, brush on cement. You do not need much, but coat all the way around.
3. Push the fitting on and twist it about a quarter turn. It will lock quickly, and in a few seconds you will not be able to move it.

Now build the pieces:

1. Glue an end cap onto one end of four of the 8" pieces. One of those caps is the one with the valve.
2. While the cement sets, hold the valve piece tipped downward so extra cement drips out and does not run into the valve. It does not matter which piece ends up with the valve.
3. Glue a tee between two of the capped pieces. Their open ends go into the two straight-through ports of the tee.
4. Glue a plain 8" piece into the tee's remaining port. That is the arm of the T. Leave its end open.
5. Repeat with the other two capped pieces, a second tee, and the last 8" piece.

You now have two T-sections. One has the valve in one of its ends.

• Four end caps cemented on
• Two T-sections built, each with an open arm
• Valve cap has no cement in or near the valve

Step 4: Create the seal#

The bottle seals against a slight bulge in the rail. The bulge only needs to be small, because the pipe is already nearly the right size for the bottle's opening.

1. Measure 10" from one end of the whole pipe and draw a line there with the marker. That end points up on the finished launcher.
2. Light the candle and make sure it is stable, or have a friend use the lighter for a steady flame.
3. Warm the pipe at the line with the flame. Keep rotating it so the entire circumference heats evenly. Be patient.
4. When the pipe is soft, apply gentle pressure along its length to push a slight bulge into it. Do not touch the pipe close to where you are heating it.
5. Hold the pipe as straight as you can while it cools. The bulge becomes permanent as it stiffens.
6. Slide a 2-liter bottle onto the rail and check that it makes a good seal.

• Line marked 10" from the end that will point up
• Slight bulge formed and cooled
• Bottle seals on the bulge

Step 5: Assemble the base#

1. Cement the third tee onto the bottom end of the rail, the end opposite your 10" line. Stand the rail upright so the tee's two open ends point left and right.
2. Cement the valve T-section onto one of the open ends of the center tee. Push the open arm of the T-section into the tee, set it flat on the ground, and use the square to check that the rail is vertical. Hold it there while the cement sets. It does not have to be exact. If you want the rocket to fly a little farther down range, you can lean the rail slightly, but upright is the simplest.
3. Cement the second T-section onto the other open end.
4. Check that both T-sections lie flat and square, then let the base set.

• Rail upright in the center tee
• Both T-sections attached and lying flat
• Joints left to dry

Step 6: Make the zip tie strip#

Six zip ties will grab the raised lip on the neck of the bottle. You first stick them to duct tape so they stay evenly spaced.

1. Cut a piece of duct tape long enough to go around the pipe at least once. Wrap it around the rail, or a scrap of 1/2" pipe, and lay it back on itself.
2. Mark with the permanent marker where the end meets the rest of the tape, then peel it off. The distance from the mark to the other end is the length around the pipe. Set it aside.
3. Lay the tape sticky side up. Put the first zip tie at the mark and a second at the other end, with the large head end facing up. Leave about 5" of each zip tie free. You will trim them later.
4. Space all six zip ties evenly between those two. Use the ruler to keep them aligned so they all meet the lip of the bottle at the same height.

• Length around the pipe marked on the tape
• Six zip ties spaced evenly and lined up with the ruler

Step 7: Set the band clamp and the zip ties on the rail#

1. Loosen the band clamp all the way with the flathead screwdriver and slide it onto the rail.
2. Slide the bottle you will use as the rocket over the rail and seat it on the bulge. Do not force it farther than it needs to go. Push it down until it feels like a good seal. This sets your reference height.
3. Wrap the zip tie strip around the rail and position it so the zip ties sit right against the lip on the neck of the bottle.
4. Press the duct tape down so it sticks to the rail.
5. Lift the bottle off.

• Band clamp loosened and on the rail
• Zip ties positioned at the lip of the seated bottle
• Tape stuck to the rail

Step 8: Make the spring#

The spring is cut from the second 2-liter bottle. It keeps the firing collar up while you pump.

1. Start a slit in the bottle with the box cutter. Then cut around with scissors to free a piece.
2. Near the center of the piece, trace the inside of the 1 1/4" coupling with the marker.
3. At the other end, trace around the outside of a 1/2" pipe. Then trace a second circle about 1" larger around it, so the circle is big enough to fit over the zip ties. A spare pipe works, or turn the launcher upside down and use the rail.
4. Draw a line down the center.
5. Cut out the large circle. Make a slit first so the scissors can get in.
6. Do not cut the smaller circle out whole. Cut it as semicircles on both sides, and leave a small portion in the middle, so a flap hangs down. These flaps hold the spring in the band clamp.

• Large circle cut out
• Small circle cut as two semicircles with flaps left in place

Step 9: Fit the spring and the firing collar#

1. Slide the spring over the rail. If the zip ties will not fit through the hole, widen it a little. Slide it down.
2. Pull the spring down and tighten the band clamp over the flaps.
3. Drill a small hole in the 1 1/4" coupling. The video uses 1/8". PVC is soft, so it drills easily.
4. Thread the nylon string through the hole and tie it off. Nylon frays, so warm the cut end with a match or lighter to seal it.
5. Slide the coupling over the rail and over the zip ties. It rests on the spring. This is the release mechanism.
6. Thread the string down through both holes in the spring. They should be big enough, since they already had to fit over the zip ties.
7. Run the string under one side of the PVC base. That lets you stand off to the side and pull.

• Spring clamped to the rail
• Coupling on the rail, resting on the spring
• String through the holes and under the base

Step 10: Load and fire#

1. Put water in the rocket bottle.
2. Put the bottle over the rail.
3. Pull the firing collar down until the rocket seats and the zip ties are over the lip. Let go. The spring pushes the collar up firmly against the rocket, and that holds the bottle in place while you pump.
4. Connect the bike pump to the valve and pressurize the rocket. Stay at or below 60 psi.
5. Stand to the side, away from the rocket, and pull the string. The collar drops, the zip ties release, and the rocket flies.

Troubleshooting#

The valve will not pull through the hole. Use pliers and a rag, and keep pulling. The video says it may take some work. When the little rim on the valve pops out, it is through.

Air hisses out where the bottle meets the rail. The bulge may be too slight or in the wrong spot. Check that the rocket bottle sits on the bulge and seals before you fire.

Water is leaking out after I start pumping. The zipties my not be set at the right height allowing the rocket to come off the bulge slightly.

Air leaks from the base. Brush soapy water on the joints and the valve while the launcher is lightly pressurized. Bubbles show the leak. Let the air out before you fix it.

The zip ties will not go through the holes in the spring. Widen the holes a little.

The rocket releases while you are pumping. The collar has to be pushed up firmly over the zip ties by the spring. Check that the band clamp is tight on the flaps, and that the spring holds the collar up.

The rocket will not release when you pull the string. Check that the string runs freely through both holes in the spring, and pull from the side so the pull is straight down.

What is next#

The launcher is built. Next, build the rocket with foam fins and a heavy nose cone.