F44AA Romulus Pulse rifle 3d design and build

paulsboutique

Sr Member
Seeing as the hype of Romulus has now died down, and the also seemingly endless posts of who got the F44 out first, I thought id spend some time and have a go.
I also wanted to create a functional prop, again highlighting just what can be achieved with 3d design and printing. I didn't want it to be "just another lump of plastic with external only detail" . Will this lead to an overly complex build .... more than likely :p

First things:
Like the M41A, I would like to have an underlying design with shrouds over the top that can be disassembled and possibly customized.
Full sounds and lights with working counter.
working targeting screen.
removable mag and mag release.
two position trigger assembly as per the movie.
movable charging handle - as per movie.
options to have front grip and torch be removable and have other attachments ie : tacticool rail...
option to have a different stock ie: non Auto Aim
the rear stock to be sprung and opens when released including the wings - to replicate the movie.
Assembled with bolts and screws - little to no glue.

Internal design considerations:
-They don't go into the internal design in the movie except for mentioning the electronic rotating breech and the 450 round capacity.
This means its not an open bolt design like the Thompson, so mag placement is not critical and does not need to line up with the barrel.
- This build will possibly need an esp32 for targeting screen, an arduino, or a second esp32 for sounds management and the round counter, Mp3 board, speaker and battery.
Lots of electronics to fill if using off the shelf, so movable and functional parts will be hard to squeeze in.

Ok on to the design.......
I looked around at electronic firing and movable breech designs and settled on one from a very old " forgotten weapons" clip on youtube.
I cant remember what the actual design it was from - i will find it one day ...
Anyhow caseless ammo was loaded in from mag, gas blow back moved the breech into place with the round, and set the firing pin ready to strike.

So with this design in my head ... off i go :unsure:


Screenshot 2024-09-10 201429.png
 
Basic theory of operation:
The idea behind my design is based on gas blow back and a loose interpretation of the above movable breech.
ie: gas down the barrel diverted at the front and runs along the tacticool rail past the gas regulator and pushes the round from the mag into the breech mechanism. Breech loads round above and electronic firing pin does the rest.




F44 v150 - no upper.png


F44 breech.png
 
Evolution of the trigger assembly:
After I got the basic shape of the grip and lower, I started on the trigger assembly. I based it around the pivot plate and mag release from the Thompson m1A1 (which was used in the M41A). Lots of problems here, as nothing lined up or even looked like it was functional.... One of my biggest peeves is when prop designers stick things on scifi props to make them look cool, but don't really think about why it would be on there in the first place.

F44 v200.png


F44 v200-1.png


F44 v300.png

F44 v350.png

F44 v370.png

F44 v370-1.png




This is the final version of the trigger assembly:
- It has the the two position trigger and safety.
-two micro switches for electronic actions.
It all bolts together much the same way as an original Thompson M1A1 with the pivot plate holding most of the assembly in.

F44 v656.png

F44 v656-1.png

F44 v656-2.png

F44 v656-3.png
 
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Upper Receiver:
I wanted to try and keep in with the design of the M41A and its use of the Thompson M1A1.
The upper slots to the lower frame in the same style as the M1A1.
The basic design is quite similar to the the M1A1 upper , but i feel not as refined and simple, which sort of makes sense as this was a precursor.

F44 v656-upper.png

F44 v656-upper 2.png

F44 v656 - upper 3.png

F44 v656 - upper 4.png

F44 v656 - upper5.png
 
Front detail and shrouds:
In my quest to try and have a practical use for all of the greebles i decided that the rear block under the front shroud was the gas regulator.
Also at the same time trying to sort electronics, i need a place for a speaker, so the only location is on the upper tacticool/gas rail, so added in a mount.
F44 v656-front.png


F44 v656-speaker.png



Next up was the front shroud:

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F44 v656-shroud-front.png

F44 v656-fr2.png



Added in Top shroud mount, front iron sight and front barrel vent.
Front shroud slides on and is held by four screws at the front and two at the side.


F44 v656uu.png

F44 v656-vent.png

F44 v656-vent2.png

F44 v656-v3.png
 
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I spent some time looking around at screen options for the side ammo display and came across some generic 1.9 inch ips screens from Ali Express.
They are slightly larger than my idea of screen size, but im thinking i can use jpegs to display the bars and set the screen black size that way, or the shrouds will block the unused portion of the display.

screen.png

outer.png

lower.png

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Lower shrouds and mag well:
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sssss.png

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I decided to put the 7.4v battery in the mag well. i also need a mag guide and someway to mount the magazine release.
In one of Andrew Bradbury's awesome renders, he has the mag out and it shows a bit of detail.



mag guide.png

guide2.png



Mag release is sprung and uses the two levers on the outside of the mag well.



release.png

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mmmm.png

side.png
 
Front Torch was pretty straight forward. I based it around a WS2812B LED which is 5v, wired to a 3.5mm jack on the right. This way i can pass power, negative and data wires back to the main mcu and not need a separate power source. I have provisioned a space for a reed switch and magnet so i can switch it manually if needed.


torch.png
 
Auto Aim screen:
The plan is to try and replicate at least some of the functionality of the auto aim tracking screen. Again the 1.9inch IPS screen fits the area and will work with esp32 and esp-cam to display a live feed. I will need to mod this area to accommodate the inclusion of an esp-cam once i figure out how to get a reliable cable length.

target.png

auto4.png


auto2.png

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Thankyou everyone ! I know its over the top, but I'm really enjoying this build so far.

Breech and rear piston assembly:
Due to the lots of wires from the screen and the micro switches for the trigger, the size of the breech will have to be limited.
I have designed in a catch for "locking" the charge lever, but it may need to be tweaked or i may remove it. Rewatching Andy's part where he re-cocks the rifle, it doesn't seem to need the catch, so it may be superfluous anyhow....
Rod is a 3/16th threaded rod through a 5.5mmOD tube, the breech then freely slides on it with the spring returning it to the closed position.

The 3 rear pistons are also held together by 3/16 rod.

breech.png

breech2.png

breech3.png

piston.png

piston2.png

piston3.png
 
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