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Modular 1/25 Scale A4/V2 model rocket

by mechg, published

Modular 1/25 Scale A4/V2 model rocket by mechg Aug 24, 2017
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Summary

The A4 rocket was developed by German scientists, including Werner Von Braun, during the 1930s and early 1940s. It was adapted for use as a weapon by the Nazis in WWII and renamed the V2. After the war it was used for research and helped pave the way for space programs in many countries.

This model is hollow with 1.2mm thick walls, allowing for two extrusion widths of .6mm. The Slic3r settings for some of the parts use an extrusion width of .63 to ensure good bonding between inner and outer walls. I used the Slic3r engine within Repetier for this project.

The entire rocket is 22" tall and 2.75" in diameter. The mid-section and fin sections are each about 7.6" tall. When printed at 100% scale, the fins fit within a print diameter of 6.2", just fitting within the print volume of an Orion Delta. Quarter-turn bayonet fittings connect most of the parts. The groove in the bayonet fittings includes a locking bump that will help lock the parts when turned 90 degrees. Index markers on the outside of the rocket help with alignment for assembly/disassembly.

Both the nose tip and nose cone base will bayonet-lock to the nose cone. The nose cone base then slip-fits into the mid-section. The jet-vanes assembly friction-fits into the tail of the rocket.

This model is mostly for display purposes, but I have added some features that should make it possible to use it as a flyable model rocket. The nose tip has a compartment for adding weight to position the center of gravity properly for stability. It is the same diameter as U.S. quarter coins, and will hold up to 136 grams in coins. The fin section has supports so a motor tube with 2.6" and 1.9" centering rings can be held in place when the mid-section is attached. Then, you would be able to swap motor mounts for 24mm or 29mm motors. You would need to file/cut four notches in the outer edge of the upper centering ring so it could be inserted past the four bayonet bumps.

The mid-section has an internal lug where a shock cord/static line could be attached. I have posted two versions of the mid-section, one with external 3/16" launch lugs and one version without.

I have included a verson of the nose tip that has the modified Wac Corporal second stage used in Project Bumper at White Sands and Cape Canaveral. It is just shy of 9" tall. I sloped the trailing edge of the fins of the Wac Corporal to make it printable without support. To make it truly scale, you would need to trim them to be perpendicular to the rocket body. http://www.wsmr-history.org/bumperaction1.htm

There is also a version of the mid section that has a simulation of the thin perforated section seen on many V2's. See Mid-ring.stl

If you build one of these to launch, please post photos and video of your rocket in action. I will seriously consider requests for modifications to the design that will help make it flyable.

Historical information and blueprints of the A4/V2 can be found here:
http://www.v2rocket.com/start/makeup/design.html

Print Settings

Printer Brand:

SeeMeCNC

Printer:

Rafts:

No

Supports:

No


Notes:

See the Slic3r settings I have uploaded.

Copy the Slic3r settings files into the filament/print/printer folders at
C:Users > yourID > AppData > Roaming > Slic3r

If you are thinking of printing this rocket, the first thing you should do is use the Test Slice file to check your slicer settings. It allows you to quickly iterate through tests of the critical part of the fin section without having to commit to a long print. The entire fin section takes about 6 hours to print at 45mm/second, while the Test Slice only takes maybe 15 minutes to print enough for you to check the quality.

It is important to set the "Only Infill where needed" box to unchecked/OFF, even when infill is set to 0%. Infill extrusion width should be zero, also. This will eliminate a lot of tiny bits of plastic that Slic3r puts in the corners of fillets reducing z-banding on the outside surface caused by unneeded travel moves and retraction.

A 5% Archimedean chord infill setting provides reinforcing ribs in the fins to make them strong at a minimal weight penalty. I tried using the Cura slicer, but it does not have a fill-in pattern that is as good as Archimedean chords is for this purpose. Other patterns might add strength, but they also add weight. This rocket is stubby with small fins, so the lighter you keep the fin section, the less weight you will have to add to the nose for stability.

When you slice each part, you must place it in the orientation shown in the third photo to avoid the need for support material.

If you get the warning that the fin section is not manifold, you can ignore this and go ahead and slice it, at least with Slic3r.

When printed on the Orion Delta using MARS PLA, the fin section depends upon retraction to keep oozing and stringing to a minimum. But the frequent retractions can cause the hot-end to partially clog, resulting in under-extrusion on the cylindrical parts of the fin section while the hot-end is catching up.

I solved this by using the retraction setting that pushes .5mm extra filament after retract. The price you pay for this is some extra material at the ribs within the fins. This is mostly hidden anyway, but you may have to experiment with that value to prevent the ribs from showing through on the outside of the fins, especially if you have a different printer or use a different filament. If a few of the ribs poke through, and you are using PLA, it is usually easy enough to sand the outside of the fin down to make them smooth.

If the bayonet fitting is too tight, you can sand the groove using sandpaper wrapped around a pen, or you can use a small candle to rub some paraffin onto the tight areas. You don't want to force a really tight fitting, because you run the risk of friction-welding the parts together and you won't get them apart again.

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what is the mid ring supposed to be? it seems to be a mid section with a little more detail but only "with lugs" ???

It just has the additional detail of perforations that are seen on some V2s. I just posted a WWII-era photo that shows it clearly. It's the last photo in the series. On the .stl file, the perforations only penetrate the skin halfway.

Cool a version without lugs? Also all these are rotated sideways I assume this is one of your first Fusion 360 once since Fusion 360 just loves doing that :-)

Hello, I love that finally a V2 model has been made with the controll fins near the engine exhaust. I have been looking for a realistic V2 model for quite some time.
could you perhaps go one small step further in realism and make a bottom piece with the nozzle geometry of the rocket engine?
It would probably be a small amount of modelling but it would be so much cooler as a display piece when people have it in their hands.
If you dont feel like it, could you please send me the bottom file in step format, so i can give it a shot?

Demy

Do you mean the Jet Vanes.stl is the one you would like to modify?

no, i like the jet vanes as they are, i would like to see the rocket engine geometry if i look at the bottom of the rocket, here i now see a large hole.
if perhaps you could send me the fin section stl, i would love to give it a try

I have uploaded both the fin section and the jet vane section in step format. I would hope you could design the nozzle detail so that it can be printed separately and inserted into the fin section. Perhaps combined with the jet vanes as one object? - just a suggestion, that's up to you.

I have updated most of the files with finer mesh versions now. You may see a few weird artifacts on the surface of some parts, but they are minor. Please let me know if there are any issues that need to be dealt with.

Finally, a nice model of the V2. And a flying one at that. Thank you. I was noticing that the curved parts are showing a fair bit of faceting instead of a smooth surface. Could you post .step (.stp) files?

Ok, I found how to create a mesh object with finer tessellation before exporting an .stl file. Hopefully I can update the .stl files with smoother versions tomorrow. I'm still learnin'....

Thanks for posting the nose cone in .stp. I opened it in Fusion360. The exterior looks perfectly smooth, but it treated the bottom of the cone as a flat surface instead of showing the internal geometry. I can see the outlines of the internal geometry. I think with a little work I could get in there and fix it. BTW, Autodesk allows a free license to non-professional Makers under their education licensing. I tried FreeCAD and it was too buggy. I found Fusion360 to be vastly better. Exporting high resolution (high polygon count) STL meshes is very easy.

Robert, I have uploaded a "Fin Section Hi-Res.stl". Please take a look and see if it works OK for you. In the meantime, I will do the same for the nose cone. Having it output a mesh with surface deviation of .03 seems to smooth it considerably while only increasing the file size by about 25%. I could go even finer, but I think it is now below the threshold where you would notice the faceting on most 3D printers.

I was just about to make the leap to Fusion 360, but I have so much time invested in FreeCAD that I think I will continue trying to make it work, at least for a few more days. When making a nose cone or tail cone with a spline curve, extruded 1.2mm and then rotated 360 degrees, FreeCAD would introduce some weird tesselation artifacts (big dents) when the cone is fused with the fins. I ended up making the fin section and nose using four 90-degree rotations of an extruded spline curve profile to avoid these artifacts. But now converting this to a finer mesh causes issues with Slic3r at the boundaries of the four sections. According to some tests I did today, it looks like I just have to change those sections back to single 360-degree rotations to make generating a finer mesh possible and have it be slice-able with Slic3r. The finer mesh settings seem to eliminate the original dent artifacts. Give me a couple of days to play this out, and hopefully I will have some smoother stl files to upload.

FreeCAD does not seem to want to smooth the surfaces no matter how I set tessellation. I have uploaded the nose tip in .step format for you to work with. If you have tools that can smooth it , ( I see that you mention Fusion 360 in your profile) I would like to hear about it.

It may have something to do with how I created the nose and fin sections - I made a spline curve for the profile, extruded it for the wall thickness (1.2mm), then rotated it to create the shell.

Before I do that, let me see if I can get FreeCAD to output smoother .stl files. I should be able to tweek the tesselation factor to reduce the bumpiness. On the models shown, after sanding to remove layer lines, priming and painting, what remained of the faceting is barely noticeable. If anything, I think it adds to the authenticity of the model, since most of the V2's you see in photos at museums have a lot of bumpiness because of the thin sheet metal skin.

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