Cores
Design requirements for Cores
The Core must:
Interface with the bottle
Hold pressure
Transfer launch forces to the Base
It was the most challenging aspect of launcher design due to high stresses and pressures in a constrained space. This section describes the evolution of Cores in general, with links to discussions about particular Cores and archived assembly instructions.
Alpha/Beta Inseparable Cores
Early prototypes focused on initial basic functionality of the launcher. These tests uncovered what aspects would be easy or hard.
Initial design goals: physically fitting to the bottle; holding pressure; not breaking during use. Using proven techniques like PVC pipes, cemented fittings, and specialized plumbing adapters reduced risks of functional failure. Universality remained purely aspirational – would it even work?
Cores in this version could not be separated from the Base because a fitting was cemented to the bottom of the Core.
This version introduced:
Stainless-steel bolt reinforcement of Core Center
Use of O-ring (later re-sized for tire valve stem compatibility)
PVC pipe for launch tube
PVC cement bonding of printed parts to PVC and sealing of printed part porosity
Schrader valve compatibility with brass tank valves
This links to the design discussion and build instructions for the Beta version on Instructables, posted in July 2020.
Core A: LT/Cement/Sch40 PVC
Core A is the first Core that could be removed from the Base. It is a robust Launch Tube configuration Core that uses PVC cement and Schedule 40 PVC pipe. Core A remains compatible with the current launcher, though the height of the O-ring requires use of legacy clamps for bottles commonly found in North America (17mm height PCO-1881).
Building on earlier designs, it continued to use:
Bolt reinforcement of Core Center
O-ring
PVC cement
Core A introduced:
Use of tire valve stems to interface to pump
Full removability from the Base
This links to a detailed discussion of the design of Core A.
Separately archived are original Core A build instructions.
Core B: Stopper/Universal
Core B is a ruthlessly simplified Core design focused on universality. It requires four off-the-shelf parts, one 3D printed part (no supports or special settings required), kitchen shears to cut a reusable plastic straw, and nothing else. No adhesives, pipe cutters, pipes, or wrenches. Assembly can be completed in less than one minute.
Core B introduced:
Standardization of all Cores around TR414 tire valve stem
Standardization of O-ring around 15 x 22 x 3.5mm size
A region-independent Core
This links to a detailed discussion of the design of Core B.
Build instructions are on Step 3 of the Version 1.4 Instructable. They are also demonstrated in the assembly video.
Core C: LT/glueless/PVC options
Core C combines the launch tube configuration of Core A with the adhesive-free fast assembly of Core B, with options for different PVC pipes. When properly made, it has identical performance to Core A plus universal bottle compatibility without changes of Clamps. It has been stress-tested up to 100psi/6.3bar.
Due the tight tolerances required to hold pressure, it requires slight rescaling between 100-103% depending on the exact size of the PVC pipe. It is also sensitive to 3D print quality: it is crucial to have 3 walls with no voids at the start or stop of extrusions.
Core C introduced:
High-performance of launch tube configuration without requiring PVC cement
Versions for ASTM Schedule 40 pipe and EN/DIN metric 20mm PN16, with options for more
This links to Core C build instructions on Step 8 of the Version 1.4 Instructable. Detailed design discussion may come as bandwidth allows.
Summary
Each Core optimizes for different priorities. Cores B and C are recommended for new builds. The launcher's modularity allows for easy development of new Core designs.
Click through links above for more information about Cores, or move on to design notes about the Base.