3D Printed Water Rocket Launcher

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Introduction: 3D Printed Water Rocket Launcher

This is a water rocket launcher built from 3D printed parts, PVC pipe, and readily-available off-the shelf components. It launches standard soda/seltzer bottles found in the US. Water rockets, also known as soda bottle rockets, are fun and great catalysts for STEM learning.

This launcher design features a robust and portable design with parts that can be disassembled and swapped as desired. It holds the bottle securely on the launcher until a launch pin is pulled. It has been repeatedly tested past 100psi.

The assembly may look daunting at first, but almost all of it simply involves snapping together 3D printed parts. The hard work of holding high pressure is isolated to a Launch Tube assembly which can be mass-produced by an intermediate tinkerer.

This is version 1, which replaces the previous public beta version. Designed with Autodesk Fusion 360.

This Instructable provides an overview of construction and use. To reduce clutter, I've put the detailed instructions and design discussions at https://magicsmokestat.com/water-rocket-launcher/.

SAFETY DISCLAIMER: 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. Pressurized systems are inherently dangerous. Do not attempt without appropriate qualifications, protective equipment, and tools. 

Supplies

Non-printed part details and sources available at https://magicsmokestat.com/water-rocket-launcher/parts-list-non-printed/.

Printed part models available for free at Thingiverse: Thing 4949248

Non-printed parts:

  • PVC pipe, 1/2″ nominal, Schedule 40, 3 ft (not shown above)
  • TR414 Tire Valve
  • O-ring, 7/8″ OD x 11/16″ ID x 3/32″ thickness
  • Machine screw, 1/4-20 thread, 2.5″ long, Hex head, stainless steel
  • Lock nut for 1/4-20 thread with nylon inlay, stainless steel
  • Rubber bands, size #33 (3 1/2″ x 1/8″) silicone preferred, but most office rubber bands will do
  • Cord for Launch Pin, braided polyethylene 36″-long suggested
  • Air pressure short extension hose, 6-8″ (suggested)
  • Air pressure long extension hose with pressure release valve, 4-6 ft (suggested, not pictured)
  • Air pressure source with pressure gauge and Schrader valve (bike pump, not pictured)
  • Food-grade oil for O-ring lubrication (suggested, not pictured)

Tools/work supplies:

  • Disposable gloves
  • Permanent marker
  • Cotton-tipped swabs
  • 120-grit sandpaper
  • PVC primer/cement
  • Paper towels
  • PVC pipe cutter that makes straight edge cuts (two options shown above)
  • Ruler
  • Utility knife (not pictured)
  • Slip-joint pliers (optional, but occasionally useful)
  • Lighter/matches to fuse ends of cords to prevent fraying (optional, not pictured)

Printed parts:

  • Wrench qtr-20 (blue): 7/16″ hex wrenches for 1/4-20 bolt and nut
  • Base (rose gold): Launcher base
  • Collar (cyan): Retaining collar for Clamps
  • Carrier (blue): Holds the whole kit together for transport
  • Pegs, long (x3, blue): Ground pegs to anchor the Launcher into grass. A short Peg model is also available.
  • Foot (x3, red): Foot for end of PVC pipe Legs that have a retaining ring for Pegs and a bevel to lock into the Base for transport
  • Clamps (x6, red): Clamps that hold the Bottle to the Base
  • Launch Pin (blue): Pin that holds up the Collar that holds in the Clamps which hold on the Bottle which swallowed the fly
  • Valve Holder (blue): Holds the TR414 Tire Valve in place
  • Valve Backstop (blue): Keeps the Tire Valve from sliding into the lower Launch Tube
  • Tube Core (blue): Interface between top and bottom Launch Tubes and interface between Bottle and Base

Step 1: Prepare Parts for Launch Tube Assembly

The Launch Tube is the most critical part of the Launcher. It is the only part to hold pressure and the only part where assembly is time-sensitive. For maximum strength and reliability, it is best assembled by an experienced tinkerer.

  • Prepare PVC pipe. Cut 3" and 5" sections of pipe. Ensure ends are square and rounded.
  • Assemble the Tube Core by inserting the bolt and attaching the nut as shown with the 3D printed hex wrenches. Carefully note the nut should go on the "bottom" side which has the bevel in the center.
  • Cut the TR414 tire valve as shown to remove the rounded "mushroom" side.

Step 2: Assemble Launch Tube

Gather the pictured materials in preparation for the bonding steps. This is the trickest step. I recommend reviewing the detailed instructions.

  • Bond #1: 3" Lower PVC pipe to bottom (beveled side) of Tube Core
  • Bond #2: 5" Upper PVC pipe to top (flat side) of Tube Core
  • Apply extra cement to the Tube Core to allow wicking action to fill gaps in the print
  • Wipe away excess cement
  • Insert the Valve Backstop in the 3" Lower PVC pipe
  • Partially insert the tire valve
  • Apply primer using a cotton swab
  • Bond #3: Valve Holder to the 3" PVC pipe to hold in the tire valve
  • Compress the entire assembly for 1 minute
  • Allow 45 minutes to cure
  • Install the O-ring in the groove

Whew! The hard part is over. Consider making several Launch Tubes at once.

Step 3: Assemble Base

The Base holds the Launch Tube in position and uses Clamps to keep the Bottle on the launcher until the Launch Pin is pulled.

  • Put Clamps in place; hold temporarily with a rubber band.
  • Slide the Collar over the Clamps partially, lining up the "PIN" notations on the Collar and Base, remove the rubber band, then press the Collar all the way down
  • Loop rubber bands around each leg support and over the hooks on the Collar

Step 4: Assemble Legs and Stow Parts With Carrier

Assemble each leg x3

  • Insert the Foot into one end of a 8" PVC pipe. Stow a leg in the other.

Stow all parts in the carrier

  • Insert Launch Tube
  • Hold the Legs vertically, sliding each Foot behind a cross-brace and fitting into the groove in the Collar
  • Put the Carrier over the end of the Pegs, lining up the "PIN" notation with the Base
  • Slide the Carrier downward into place
  • Stow the Launch Pin and wrap the cord around the cleats
  • Stow an optional Hose Extension
  • Add an optional clip

Step 5: Set Up Launch Site and Launch!

Find an open and flat grassy space away from trees and traffic.

Set up the Launcher

  • Insert the Legs into the Base
  • Position the Base on a level surface
  • Stabilize with Pegs (in grass) or heavy objects (on hard surfaces)

Load the Rocket

  • Insert a Launch Tube into a Rocket
  • Load the Rocket + Launch Tube onto the Base
  • Lock the Rocket in place by raising the Collar and inserting the Launch Pin

Prepare for Launch

  • Ensure the launch site is clear and that no one is near the launcher
  • Pump up the Rocket. Some slow leak is possible (and safer!) and not a problem.

Launch!

  • Pull the cord to the Launch Pin. Blast off!

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. You can use a thin object (the Carrier's cord cleats work well) to press the Schrader valve's center pin to release the pressure. As a final backup, most Launch Tubes will have slow leaks from microscopic air passages in the Tube Core. You can wait for the system to depressurize.

Step 6: More Ideas

The above is a brief overview of assembly and use of the Launcher. Many more details can be found at https://magicsmokestat.com/water-rocket-launcher/.

Feel free to ask questions below and I will do my best to answer.

Please share your builds below! Also let me know if you are an educator and interested in further developing this project for your students.

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    8 Comments

    0
    JamesD125
    JamesD125

    12 days ago

    I love this - thank you very much. I’ve been making water rockets for many years (for local Cub and Scout money raising activities) using zip ties and a plastic ring as a launch release mechanism but your design packs away much smaller and will be great. My old ones were also getting tired.
    I’m printing 4 - slightly modified the core and feet to match suitable UK pipe sizes and bottle necks.

    0
    MagicSmokeSTAT
    MagicSmokeSTAT

    Reply 11 days ago

    So glad you're finding this helpful! I'd be very interested in the design works for you
    as well as your modifications for making it in the UK. My pipe (ha!) dream is to make and publish localized designs that can be made easily no matter where in the world you are. Please reach out by direct message if you have time to share. And please share your builds on Instructables when you're done!

    0
    mrpesas
    mrpesas

    15 days ago on Step 1

    What is the purpose of the Bolt and Nut in the Tube Core? I'm assuming it is just to add strength to the 3D printed part, but I wanted to check. Thanks

    0
    MagicSmokeSTAT
    MagicSmokeSTAT

    Best Answer 15 days ago

    That's exactly right. 3D printed parts are weak to tensile forces across layer lines. I haven't found a way to make a 3D printed part that reliably handles the stresses that meet at the Tube Core without an addition that specifically holds the tensile forces. Similar to rebar in reinforced concrete.

    Picture attached of what happened in an early prototype shortly after a (non lock-)nut came loose showing fracture along a layer plane.

    More discussion about the design of the Tube Core here: https://magicsmokestat.com/water-rocket-launcher/d...

    IMG_1154.jpeg
    0
    Ranuga
    Ranuga

    15 days ago

    Good job. Whats is the maximum pressure? Are there any rocket guide rails for 2 or more stage rockets?

    0
    MagicSmokeSTAT
    MagicSmokeSTAT

    Best Answer 15 days ago

    Hi Ranuga! Thanks for your question. Maximum pressure will be dependent on your specific build, particularly with the Launch Tube. The clamping system is over-engineered to be very robust and I have never had a clamping failure, even with earlier versions where the clamps were less beefy.

    In my own stress testing, I have exceeded 80psi many times with no issue. I have gone past 100psi and never had pressure-related launcher failure. Your experience may vary, and I am especially interested in everyone's (safely-performed) pressure testing and failures. Sharing those will help improve the design.

    Note that you should generally not exceed 50psi with plastic bottles due to risk of the bottle bursting - especially with larger bottles (larger diameter leads to higher bottle wall strain).

    Note that there is usually a very slow leak in the Launch Tube. This is by design (or rather, isn't a construction defect if you experience it). It is caused by the porosity of 3D prints, and generally doesn't cause issues especially if PVC primer/cement is applied generously to the Tube Core to wick into the microscopic passages.

    Please let me know if you experience otherwise so I can offer specific suggestions.

    You can find more discussion about maximum pressures https://magicsmokestat.com/water-rocket-launcher/,... including a Launch Gallery with higher PSI test launches and a lot more technical discussion that would clutter this Instructable.

    Regarding rocket guide rails - not yet! But that's a great idea and would be a great extension to the project. That said, the launcher base is compact enough that you could hammer guide rails into the dirt right next to the launcher and it may do the job.

    You could also do boosters by putting several launchers together and tying together their launch pins. The options are endless.

    IMG_3440.jpeg
    0
    DavidL868
    DavidL868

    Tip 17 days ago on Introduction

    A slight modification to consider would be to use a Presta bicycle tire valve from a road bike tube instead of the Schrader valve, and a floor pump with a head that can accept a Presta valve. Presta valves are designed to hold higher pressures. For safety, DO NOT EVER pump these to higher than 150 psi. Also, be aware of any modifications that could structurally weaken the plastic bottle, such as heat (from hot glue) or some adhesives.

    0
    MagicSmokeSTAT
    MagicSmokeSTAT

    Reply 17 days ago

    You could definitely use a Presta valve also. I haven't yet come up with a way to adapt this to a 1/2" PVC pipe without making the Launch Tube not removable from the Base, but I'm sure someone will find a way (or just decide that removability isn't that important the application). The design is meant to be flexible and extendible. I'm looking forward to seeing people's designs.

    Regarding maximum pressures for the Schrader vs. Presta valve: I think this is less of an issue at intended launch pressures, but maybe when the performance envelope is stretched hard it'll become one.

    Great advice about the plastic bottle. Some of my hope with an eventual Fin Mount design would be attaching fins without requiring additional adhesives or hot glue. That's an ongoing project. Most guides recommend a 50psi pumping limit and replacement of the bottle after 10 uses.

    Thanks for your comment! Love the ideas and input.