Simple 3D-Printed Water Rocket Launcher

This is a water rocket launcher system that:

• assembles in minutes from snap-fit 3D printed parts without glue
• is globally-compatible with all soda bottles
• is one-hand portable
• is PVC-pipe optional
• costs less than $10 USD for materials

3D models and latest updates are at Printables.

Detailed design discussions are at https://www.marimolabs.com/water-rocket-launcher

Design Concept

Launching a soda bottle water rocket requires water, pressurized air, and a triggering mechanism. 3D printing is perfect for interfacing cheap off-the-shelf parts to do this reliably and simply.

This launcher system is composed of two subsystems: the Core and the Base. The Core slides into the bottle to hold pressure. You can choose a region-independent stopper-style design or a higher-performance PVC pipe launch tube-style design. The Base provides triggering and anchors the rocket to the ground. The Core is easily removed from the Base to simplify loading of rockets.

Safety Disclaimer

Pressurized systems are dangerous. No warranty, expressed or implied, is made regarding the safety, performance, or suitability of any designs, models, or analyses presented. I am not an expert and hold no formal qualifications in this field. Do not attempt without appropriate experience, protective equipment, and tools. 

Non-Printed Parts

• TR414 Tire valve stem
• O-ring 15mm ID x 3.5mm thickness x 22mm OD
• Rubber bands, e.g. silicone #33 (3 1/2" x 1/8")
• Cord to tie to Launch Pin, 3 meters, e.g. paracord
• Tire valve extension hose, 5-8.5"
• Reusable straw, 7.6-8mm OD (for Core B)
• not pictured: bike pump with Schrader (car tire, mountain bike) valve connection
• not pictured: bike pump hose extension, 2 meters (optional but recommended)

3D-Printed Parts (Download Link)

• Base
• Collar
• Clamp x6
• Core B (recommended for first builds)
• Launch Pin (not pictured above)
• Leg x3
• Peg x3
• Carrier
• Schrader valve removal tool

Optional Parts

• For Core C: 20cm of PVC pipe for launch tube (see Printables for Part Selection compatibility chart); utility knife for cutting valve stem. See Step 8.
• To substitute PVC pipe in place of printed Legs to save filament: Print Foot x3; PVC pipes 15-20cm x3. See Step 9.

This Instructable elaborates on each of the steps in the assembly video above for Version 1.42 (August 2023).

Notable updates from previous v1.2

• Universal Launcher design. Fully region-independent universal Clamps and 3D-printed legs are now the default.
• Retirement of Core A (launch tube design requiring PVC cement) for Core B (universal) and Core C (launch tube not requiring adhesives)
• Full redesign of Core C for reliability
• Clamp and Collar redesign for rigidity and universality

Gather Parts

• Base
• Collar
• Clamp x6
• Rubber bands x3

Assemble the Base

• A: Put Clamps in place; hold temporarily with hand or a rubber band
• B: Slide the Collar over the Clamps partially, lining up the "PIN" notations on the Collar and Base
• C: Press the Collar all the way down until it snaps into place
• D: Loop rubber bands around each leg support and over the hooks on the Collar (3x)

Gather Parts

• 3D-printed Core B
• TR414 car tire valve
• O-ring
• Hose extension
• Schrader Valve Tool
• Reusable drinking straw

Assemble Core B

• A: Put O-ring on TR414 tire valve just below the cap
• B: Insert tire valve into Core Type B printed part
• C: Securely attach the air hose extension
• D: Seat the tire valve in the 3D printed part with a combination of pushing and a tug on the extension's collet (spinny part). Don't pull too hard on the extension hose - it may come apart depending on the strength of the crimp.
• E: Insert the reusable straw
• F: Remove the springy valve in the air hose extension with the Schrader valve tool (this improves safety for a launch abort depressurization)

This launcher is designed for portability. A Carrier locks all parts together so nothing gets lost.

Gather Parts

• Launch Pin
• Cord, 3 meters
• Carrier
• Legs x3
• Pegs x3
• Base subassembly from Step 2
• Core subassembly from Step 3

Assemble Launch Pin

• Tie the cord through the hole in the Launch Pin. Secure this very well; you do not want it to come loose at launch time. This happens surprisingly often with slippery synthetic cord.

Stow Parts in Carrier

• Holding the Legs vertically, slide each Foot behind a cross-brace and fit the Leg into a groove in the Collar
• Put the Carrier over the end of the Legs, lining up the "PIN" notation with the Base
• Slide the Carrier partway down, but not yet over the Clamps
• Insert the Core
• Finish sliding Carrier downward into place over the Clamps, which will lock the Core in place
• Tuck hose extension into a leg hole in the Base
• Stow Pegs in the bottom of the Legs
• Stow the Launch Pin and wrap the cord around the cleats; tuck the loose cord end behind an inner cleat to hold in place

Anchor the Base

• Find an open and flat grassy space away from trees and traffic. Decide where you will put your Launcher and where you want the person pulling the cord to sit.
• Insert the Legs into the Base
• Position the Base noting the Pin marking
• Anchor the Launcher to the ground with Pegs. Do not skip this critical safety step!

Load Rocket on Core

• Add water to the bottle. 1/3-full is good.
• Slide Core into bottle (Core C PN16 pictured)

Insert Core into Base

• Slide the hose extension and Core into the Base until the Core and rocket are vertical

Clamp Rocket to Base

• Line up the Clamps between Fin tabs (if using)
• Slide up the Collar to clock the Clamps
• Observing the arrow on the Base, insert the Pin to hold up the collar

Prepare for Launch

• Ensure the launch site is clear and that no one else is near the launcher
• Check that the Base is well-anchored
• Check that the Launch Pin is well-seated and that the cord is tied tightly
• Attach the air pump (ideally with a long extension hose)
• Pump up the Rocket. Some slow leak is possible and not a problem

Launch!

• Re-check that the area is clear
• Count down...
• Pull the cord to the Launch Pin. Blast off!

Notes on Launch Abort

Note: if a launch abort is needed, the best thing is to depressurize the system with a pressure release valve. Some pumps have these. You can also purchase hose extensions that have release valves. If you removed the Schrader valve center from the hose instruction per the instructions, you can depressurize by disconnecting the hose at that location.

Why Try Core C?

For higher performance, you can build Core Type C. As a "launch tube" configuration Core, it uses a PVC pipe that slides into the bottle to keep the water inside for the initial phase of the launch. This provides an extra boost phase that increases launch speed 10-20% at the cost of Core construction complexity.

Core Type C requires no adhesives or hardware, unlike Core Type A (from v1.2), which it replaces. I recommend still building Core Type B as a backup, as complexity adds chances for failure.

Match the model of Core Type C to your PVC pipe: ASTM Schedule 40 (North America); DIN 8061/62 PN16 20mm metric pipe (EU); UK overflow pipe (UK; untested)

Since PVC pipe can vary slightly in dimensions, you may have to scale the print file up. It will work well with the system up to 103% scaling. Make sure to follow the print settings on the Printables page. A sizing gauge is provided for Schedule 40 pipe.

Supplies

• 3D printed Core Type C (matching your pipe; scaled as needed)
• O-ring, 15mm ID x 3.5mm thickness x 22mm OD (same as Core B)
• Air hose extension, 15-20cm long (same as Core B)
• PVC pipe, longest that fits in your bottle; I use 20cm
• Utility knife for cutting TR414 valve rubber (for Schedule 40 version)

Assemble Core Type C

1. Cut off “mushroom” part of TR414 tire valve while leaving the thin rim (skip for PN16 and UK versions)
2. Similar to Core Type B:
3. Insert the valve into the Core Type C printed part
4. Attach the hose extension securely
5. Install the O-ring in its groove
6. Push up on the hose extension so that the tire valve is pushed partly back out. This brings the thin rim away from the edge of the 3D printed part so it doesn’t get mangled on the next step
7. Insert the tire valve into the PVC pipe while maintaining grip on the hose extension so the valve doesn’t slide
8. Insert the top of the printed part into the PVC pipe as far as it goes
9. Similar to Core Type B: Remove the spring core in the hose extension

Why PVC Pipe Legs?

If you want to save printing filament and are comfortable working with PVC pipe, you can build the Legs primarily out of PVC pipe. There are no performance benefits from this option, but it gives you an option for longer Legs or modifications to the Foot for special applications. Note that longer Legs apply more torque force on the Base.

No adhesives are required.

It requires pipe with outer diameter 21.4-5mm. There are options for ASTM Schedule 40 (verified); UK overflow pipe (verified); and AS-NZS pipe (untested).

Supplies

• PVC Pipe equal sections x3, 15-20cm
• Foot x3 (specific to your pipe)
• Peg x3 (specific to your pipe; note that the universal Peg is sized for ASTM Sch 40)

Assemble PVC Pipe Leg

• Insert the Foot into one end of the PVC pipe
• Store the Peg in the other end of the PVC pipe (note that the Peg does NOT go into the Foot side, as it would with the 3D printed legs)

Stability Overview

Notice that plain bottles are unstable in flight and flip. This is because a bottle's Center of Pressure (Cp; center of aerodynamic forces) is in front of the Center of Mass (Cm). For stable flight, Cp needs to be behind Cm. We can do this by adding fins to the tail (moves the Cp back) or by adding payloads to the front (moves Cm forward).

For my testing, I've used 1-liter bottles from Polar Seltzer (or the East Coast US Trader Joe's equivalent) as a prototyping platform for 3D-printed fins and an 84mm interlocking payload system. There are many other possibilities, so don't limit yourself!

Fins

Add lightweight fins to the back of your bottle to straighten flight. Slide them onto the neck of the bottle, and zip-tie in place in the groove just below the fins.

There are three sizes for experimentation. You will notice that a having a payload (moving Cm forward) allows for using smaller fins (don't have to move Cp as far back).

Payload Mount

Add a Payload Mount (blue 5-strap star) by gently bending the straps through a Mount Shroud (purple) and zip-tying it to the base of the bottle. This provides a stable mount for Payload Modules. Stack the module on top and zip-tie around the interlock.

Bare interlock model files (orange) are available for your own remixes.

Payloads

Endless possibilities! However, I don't have endless time, and parachute modules and a camera mount are still in early development as of September 2023. Prototypes are posted, but I can't yet recommend any for routine use.

Inspiration

This project was born in June 2020 in the early days of the Covid pandemic. It is dedicated to my children, educators teaching through the pandemic, and NASA’s Perseverance mission team, all of who reminded us to dare mighty things even when the future is uncertain.

Special Acknowledgments

No project exists in a vacuum. These designs are built standing on the shoulders of giants, and based on the contributions of dozens of people who have volunteered time, ideas, testing, and encouragement.

This launcher design borrows heavily from existing designs shared by the international water rocket community, especially Air Command Rockets, US Water Rockets, and Raketfued. I am grateful for your generosity.

Also, thank you to the many people who have given feedback in the comments, shared your makes, and helped test prototypes. This project wouldn't have come this far without your help. You will see their names throughout the comments, makes, and changelogs of this page and prior Instructables and Printables.

Versions

• Current version (this page) is v1.42, updated September 2023.
• Version 1.2 was last updated July 2022, superseded by v1.42 in August 2023.
• Beta was last updated around October 2021, superseded by Version 1.0 in 2022, gradually developed to v1.2.

Additional Information

• Detailed design discussions are at https://www.marimolabs.com/water-rocket-launcher
• This project was designed with Fusion 360 by Autodesk using the free hobby license.

You! Yes, You!

Thank you for reading this Instructable. Please share your thoughts, ideas, and makes. Every bit of feedback helps to refine the design and make water rocket projects more accessible to all.