The Marimo Labs Open Access Water Rocketry Project

Designed in Cambridge, Massachusetts, USA
Free forever, everywhere
marimolabs.com
v1.44

Demo at Cambridge Science Carnival - Sept 2025

270 launches in 4 hours! [https://marimolabs.com/csc](https://marimolabs.com/csc)

New! Nosecones and fins for 0.5L bottle

Modular with different nosecone and fin options. Designed for flex filament for safety and durability.

[https://www.printables.com/model/1393152-water-rocket-parts-for-05l-polar-seltzer-bottle](https://www.printables.com/model/1393152-water-rocket-parts-for-05l-polar-seltzer-bottle)

Launcher (this page)

A full-bore water rocket launcher system designed for easy assembly and universal compatibility.

For those without ready access to 3D printers, you can purchase a kit will all parts from the Marimo Labs Store. Kits of non-printed plumbing parts are also available.

Payload/fins for 1.0L bottle

Still available on this page, below

• Video instructions above.

• Written instructions on Instructables: [https://www.instructables.com/Simple-3D-Printed-Water-Rocket-Launcher/](https://www.instructables.com/Simple-3D-Printed-Water-Rocket-Launcher/)

• Detailed design discussions at: marimolabs.com

• Read and follow the Safety Instructions PDF on the downloads page.

Disclaimer

Hey. Pressurized systems are dangerous. Know what you are doing and take appropriate safety precautions. Make your own assessment about whether this project is appropriate for what you are trying to do, and use at your own risk. Do not attempt without appropriate experience, protective equipment, and tools. Most water rocket guides recommend not pressurizing past 60psi/4 bar. Always secure the launcher to the ground. 

PARTS LIST

Non-Printed

Option 1: Marimo Labs Store (shipping within the US)

• Core Subkit with Non-Printed Parts

• Rubber Band and Launch Cord Subkit (or bring your own)

Option 2: Purchase off-the-shelf (sample Amazon links below)

• TR414 Tire valve stem

• O-ring 15mm ID x 3.5mm thickness x 22mm OD (if unavailable locally, can try TPU printable version by @lemonydes_1352490)

• Schrader (car/mountain bike) valve hose extension

• Rubber bands, any, but silicone #33 (3 1/2" x 1/8") are nice

• String to tie to Launch Pin

• Parts for specific Cores:

  • Type B Universal: Reusable straw, 7.6-8mm OD (prevents water backflow into pump but not strictly necessary)

  • Type C: 20cm of corresponding PVC pipe for launch tube

Printed

For a launcher that can be built anywhere in the world to launch all* soda/seltzer bottles in common production:

• Base

• Collar (* see note below)

• Clamp x6 *

• Core Type B *

• Launch Pin

• Leg x3

• Peg x3 (don't skip securing the launcher to the ground!)

• Carrier

* Unique to Germany are Mehrwegflaschen - a specification for reusable/refillable bottles. These may have a flange height of 23mm and diameter of 37mm, requiring special Clamps. They may also benefit from a special Core and scaling of the Collar. Please see the Clamp remix here by @LucasF_62480.  Please see Core remix and notes about Collar here by @TomTom_1424482.

CORE SELECTION GUIDE

The launcher base accepts several different “Cores”, which are the central interface to the bottle. Core B is recommended for first builds. Core C is recommended for higher performance.

• Core Type B Universal:  Universal worldwide compatibility. No PVC pipe required. 

• Core Type C Sch40: Glueless “launch tube” configuration for Schedule 40 PVC pipe. Print with 3 walls. Seams in printed parts may lead to inconsequential pinpoint leaks at high pressure. Theoretically, it may help to adjust seam position to “random”, but I have not found this necessary. 

• Core Type C PN16 beta: Similar to the Sch40 version, but for metric 20mm PN16 pipe. Print with 100% concentric infill. Do not trim the TR414 valve stem. Force the whole “mushroom” into the pipe.

• Core Type C UKovf alpha: For UK overflow 21.5mm pipe. Print with 100% concentric infill. Do not trim the TR414 valve stem. Force the whole “mushroom” into the pipe. Please tell me if this core works for you, as I do not have the pipe available to me to test. Let me know if you need to scale the file.

• Development for AS/NZS DN15 PN18 (OD 21.1-21.5, ID 17.8) pipe is suspended until there is need/interest. 

FINS/PAYLOADS

These are are sized specifically for Polar Seltzer brand 1L bottles and similar Trader Joe's (TJ's Eastern US; Western US may differ - please confirm) 1L sparkling water bottles. 

For the new 0.5L modular flex system, see here: [https://www.printables.com/model/1393152-water-rocket-parts-for-05l-polar-seltzer-bottle](https://www.printables.com/model/1393152-water-rocket-parts-for-05l-polar-seltzer-bottle)

For prototype universal fins that screw onto the bottle threads, see the prototype page.

Fins

Fins are secured with a zip-tie in the shallow groove immediately below the fins (giving clearance for clamps on the bottle ledge). These designs were inspired by @HowToHomemade's [https://www.printables.com/model/442398](https://www.printables.com/model/442398). Re-designed from scratch to allow clearance for clamps. Printable with mild challenge in TPU for durability; PETG/PLA will tend to fracture on hard landing.

• Fins PLR1L 130: 130mm diameter. 20cm2 per fin.

• Fins PLR1L 150: 150mm diameter. 28cm2 per fin.

• Fins PLR1L 170: 170mm diameter. 40cm2 per fin.

Payloads

An 84mm diameter payload system designed in 2023 consisting of the below. Lightweight but not durable. Future plans are to redesign similar to the new 0.5L system.

• Payload Mount: Uses the flexibility of thin straps to attach to the 1L bottle specified above. Insert the straps through the Shroud before fitting to the bottle and attaching with a nylon zip tie. 

• Payload Mount Shroud: Stabilizes the Payload Mount

• Payload Interlock Top/Bottom: Use for your own custom payload designs. Merge these models into the top/bottom of your payloads to connect.

• Parachute Modules are on the prototypes page, in development.

PRINT SETTINGS

Launcher Parts

• For best results, print slowly! Layer adhesion, bridging, and text quality will be better, and especially noticeable on PETG. While your printer may be able to move at ludicrous speed, filament sometimes needs more time and heat to form the strongest bonds. Limit print speeds to 75mm/s with external wall 50mm/s or set max volumetric rate to 8mm^3/s.

• Line width: 0.4-0.45mm

• Layer height: 0.20mm

• Walls/perimeters: 3 (especially Core Type C). Classic Wall Generator works best for the Base due to overhang/bridging issues with Arachne. All others can print with Arachne.

• Infill: 20% except “Core TypeC PN16/UKovf”: Concentric infill 100%

• Filament: PETG ideal (for temperature stability) but not required. PLA/PLA+ is fine, but you must protect from heat to prevent deformation. 

• Supports: None (but see Print bed adhesion, next)

• Print bed adhesion: Some parts have small footprints and may benefit from printing with brims or rafts depending on your print bed's adhesion and whether you have overhang curling issues. These include Launch Pin (the narrow parts sometimes lift off the bed) and Cores Type B/C. For Core Type B, you can consider printing upside down WITH supports touching the print bed.

• Scaling: Schedule 40 Advanced Parts that depend on pipe internal diameter (Core Type C) may need scaling. Use Gauge Sch40. Make sure there are no burrs on the inside edge of your pipe. Place Gauge on a table; put the pipe on top; push the pipe down with one finger only. Use the last covered scale factor for printing ONLY these three parts (ranges 99%-103%). Avoid the temptation to mash the pipe onto the gauge. All other parts should be printed at 100% scale.

Fins

• 1 wall, 10% infill. 3D Honeycomb infill pattern ideal, as other patterns may cause inconsistent infill in thin fins. Check your slicer preview. Concentric pattern top and bottom. Consider brims if your bed adhesion is low; consider slowing non-print travel speed if you have later detachment issues on bed-slinger printers - the aerodynamic drag is enough to move your part and cause nozzle collision.  TPU is possible for the PLR1L fin series, though more challenging with larger fins.

Payloads

• Payload PLR1L Mount: 2-3 walls for strength of attachment to bottle

• Other payload components: 1 wall, 10% infill. 3D Honeycomb infill. Monotonic pattern top and bottom.

CHANGELOG

2026-07-12: Added Collar-v142-29mm-TEST. Stretches Collar to 29mm tall for tighter fit. Please share test results in Makes/comments.
2026-04-04: Older history moved to [https://marimolabs.com/pages/wr-changelog](https://marimolabs.com/pages/wr-changelog)