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Attaching stuff to the top of the rocket
Here, "payloads" is used broadly to mean things you want to loft into the air. This can include attaches parachutes, nosecones, weights, cameras, and altimeters.
This page discusses a system of attaching payloads to soda bottle rockets. While solutions exist with glues and tape, I wanted a design that attached to a round bottle end was 3D printable and did not require adhesives.
The first exploratory version shown here is on an Alpha-phase launcher. It has an early parachute attempt made from a plastic bag and string, taped to the bottle, covered with a paper nosecone. It tore off immediately on launch.
Phase 1: Bracket for top of rocket
Goal: Design a 3D-printable bracket that attaches to the top of the rocket without glue or tape.
Flexible strap mount
The first design problem was finding a method to attach a parachute to the smooth end of a soda bottle without glue or tape. The first insight was that bottles are slightly bulbous at the end, and a belt-and-suspenders configuration may hold.
The next problem was how to fit to such a complex geometry with a 3D printed part with my rudimentary design skills. Then I realized that what appeared to be complex was a five-segment radial symmetry, and I could use the flexibility of 3D-printed straps to bend along the bottle. This also solved the next problem, which was aligning the forces experienced by the print so they would transmit tension along layers where it was strongest.
The first prototype is shown to the left, providing a loop to tie the parachute cord. Five radial straps curve along the bottle and are held together with a velcro tie. This held securely enough to move to the next stage.
Platform mount
The parachute mount would eventually need a surface to mate a nosecone, so it was extended to a flat platform. It was a little wobbly, something improved in the next phase. The platform also sprouted tabs to hold the nosecone.
Platform mount, bottom view
Bridges over the straps allow the straps to attach close to the center, providing a gentler curve.
Phase 2: Add a shroud
For aerodynamics, but also stabilizes the straps. Top blue tabs are to hold a nosecone.
Shroud locks in
Phase 3: Nosecone
Goal: Add basic nosecone to hold parachute
Blue tabs hold ring
Incredibly, it worked. Several issues which will be discussed further on the parachute page.
Phase 4: Payload interlocks
Goal: Attachable
Swappable modules
In the spirit of modularity, I modified the parachute mount so different modules could be attached. The orange circles are generic upper and lower interlocking rings that can be integrated into module designs. What was the parachute mount, with the five straps that connect to the bottle, became a payload mount.
Payload mount
The updated payload mount has a system of flanges that interlock with payload modules. Weight is reduced by skeletonizing the platform
Payload mount, internal view
Five straps secure the mount to the bottle with a zip tie. The purple shroud provides additional stability and aerodynamics.
Phase 5: Test payloads
Video. And broken stuff.
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