State of 3D Printed Rocket Design Advancement (Visuals)
Current Iteration
The initial version of this airframe relied on individual screws to secure each part. The goal of this was to allow for unprecedented modularity, but handling each attachment point and the large corresponding amount of screws ended up being more of a time sink than I anticipated. I had screws on the mind when I was thinking of ways to simplify, and so the obvious move was to make the rocket itself a screw.
Final Assembly
Each part is optimized to make assembly and reconfiguration time as fast as possible, requiring a minimal amount of tools. The part that gets swapped the most is the P1 fins component- fins with different aerodynamic coefficients can be easily threaded in. There were many design considerations that led to the optimization of the rocket as a whole.
Part by Part
Design considerations for each
significant component.
The main improvement of the simplified nose is the snap-in ability- having notches on the edge allows two screws as opposed to the previous four. The two screws on the nose and the two that hold the body hatch in are the only external screws that are modified on a per launch basis, making re-flight of a vehicle much easier.
There is no surface with an area of greater than 2mm^3 at an angle relative to the buildplate greater than 60 degrees, making this printable with no support.
P3 (Nose) with integrated inner threading. The indents on the outer diameter allow the part to be easily gripped and rotated- in the flight regime of this rocket (not exceeding mach 0.3), the ergonomic benefits outweigh the near negligible effect on aerodynamics.
The elliptical shape of the nose makes it much more impact resistant, and because the nose is the first part of the upper structure to make contact with the ground, the strength benefits outweigh the slight aerodynamic impact.
Extra screw holes at the corners are present to allow for emergency installation of the older non-snapping hatch.
The body hatch/ egg holder is one of the most important components of the vehicle. A foam insert containing a Grade A large hen egg (per the TARC rules) is inserted through the top, to the point where it stays in place but has room to be pushed. When the hatch is inserted into the body, the egg is snugly pushed into the foam. The inner wall is corrugated as is visible, making it more structurally robust while still relatively light. This setup has not yet broken an egg, even when a parachute partially opened and impact velocity was nearly twice as intended.
This design contains the same snap-in form as the nose hatch, making it, yet again, only require two screws rather than the previously needed four.
P2, the main body, is the largest component of the rocket. It is threaded on both ends, and has ample space for accommodating anything attached to the body hatch.
External slats slide on T-slotted aluminum rails, allowing for a stable exit off of the rail on launch. These slats are meshed separately in GCODE configuration from the rest of the body- the way the GCODE compiler sees it, they are separate parts. This allows me to easily set variable infill and wall thickness- in this case, the slats are two walls instead of the usual one wall to increase their reliability and prevent any likelihood of warping.
This part was initially a challenge because of it's purpose to bridge the gap between parts printed at opposite orientations. This part needed to have a completely closed off flat plane to contain ejection charge gasses on one end, and be threaded on the other, and my goal is always to minimize or completely eliminate support. I did this by printing threads down, and creating a 45 degree chamfered surface as the transition between the threads and the lower attachment faces.
A shock chord to keep the rocket together and hooked to a parachute once the ejection charge detonates is tied into the two loops on the bulkhead. Bulges on the inner diameter of the surface allow for easier alignment with the the corresponding adapter, and allow for easy adjustment of friction via. sanding.
One compromise with this design is the motor mount being less variable- on the previous designs, it was simpler to swap in a tube of a different diameter if needed, because the tube was essentially a separate part. In order to simplify the design with the specific requirements of the launch in mind, I just ended up combining everything into one part, because the only motors I was planning on flying were 24mm.
6 total screws are used to secure the bottom shock chord loops. These are rarely in play, however, because once they go in, they should hopefully never need to come out, so they don't add to the complexity in a detrimental way.
One end of the shock chord, which attaches to a kevlar line, is tied through the chute loops. Most of this part is fully solid, except for a few void spaces that otherwise provided no real structural benefit.
The orientation of the loops has allowed them to maintain full structural integrity in the face of hot ejection charge gasses.
The thinner rear-offset fins that were intended to increase the altitude. The outer edges of the fins and the joints with the body are functionally separately meshed, which allows printing at a thicker profile in order to reduce the chance of snapping on landing.
The fins thread into the 24mm motor mount. They are essentially isolated from ejection charge gasses.
The original, thicker pattern of fins. These are certainly more robust, while employing the same variable meshing techniques that I've perfected through this project.
The sweep (or lack thereof) is fairly ideal for the flight profile- you almost want to have perpendicular fins relative to the body at this speed because, at least for this application, swept wings only begin to have a positive aerodynamic effect moving into the transonic region.
The screw in motor retainer- this part is dual purpose. It not only keeps the motor from blasting out of the rear after firing the ejection charge, it helps to align the whole motor mount itself, being flush with the inner side of the fins it threads into.
The rocket motor, pressing up against the top of the 24mm mount, is held firmly into place by the screw in retainer. The indents are for ergonomic purposes.