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Custom Built AEG - Build Log


BIGBC

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Some may have been around when I was talking about my Final year project: designing my own AEG - and some of the concepts and styling that went along with it. Well I came down with glandular fever part way through that year and had to step out of Uni for a bit returning this year to finish off, so the project kind of stopped for a bit.

 

I'm now back on it and will be getting stuck into fabricating it over the next few months. Seeing as this fits in with the ACBC schedule I figured I might as well enter it :)

 

Here is a few dirty renders of where I am at atm:

 

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On the to do list:

- Stock modelling (receiver plate + catch, butt pad)

- Mag release catch

- flesh out fire selector + electronics side of things

 

Atm I intend to machine the bulk of it out of aluminium.

 

I have been planning to do make the fire selector electronic instead of utilising the mechanical selector on the gearbox as linking selector switch up from the grip back to the gearbox would be problematic. Input/suggestions on how best to do this would be appreciated.

 

Cheers, ben

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I apologise for the vagueness on this but hopefully it will make sense regarding electronic fire mode selection.

 

You're model up there appears to have an ICS L85 gearbox in it which uses a long (and thin) semi auto cut off bar linked to that particular guns trigger switch set (I'm sure you're already aware of this).

 

If the gearbox mounted cut off and the cut off bare are removed you are left with a full auto only gearbox when you close the trigger switch.

 

There are computerised mosfets out there can make guns semi auto only irrespective of the presence of a cut off lever (e.g. Extreme Fire Cheetah with Unconventional Airsoft software). The AWS raptor utilises a side mounted switch that is activated by the selector plate in full auto to let the gun run in full auto - it uses the gearbox mounted cut off lever to hit another switch to let the FET computer know a cycle has been completed. The Black Talon Concept Chimera FET I believe does away with the need for a cut off lever in that respect.

 

With the Extreme Fire type FETs these require 5 semi shots on battery connection but I think this is linked to 'teaching' the FET the guns mechanical/electronic behaivour so burst functions can be implemented

 

So, it would seem you'd need to have your semi/full auto controlled by a computerised FET with a default state for semi auto that when you put your selector to full auto, is able to receive a signal to bypass the default cut off state and runs the gun until you release the trigger. Alternatively, you could do a 'press and hold' for full auto with a 0.5 second delay which isn't a million miles off the safe-semi-burst/hold for auto conventions you get with the mosfets already mentioned.

 

Might be worth looking into how units like the ones I've mentioned and the ASCU and ARES programmable triggers work for some inspiration.

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Keen eye, it is based around the ICS L85 internals as I have a couple sets of these handy.

 

You've pretty much confirmed what I had been thinking I'd have to do - control it with a computerised MOSFET.

 

I was trying to think of a way to leave gearbox in auto and have the fire selector connect directly to a MOSFET as normal for auto, then a seperate parallel circuit which cuts off after 1 shot. Im sure i read about something similar somewhere but cant find it now :(

 

Its been 4 years since I did any element of electronics on my course :P

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If you're not familiar with embedded electronics, it will be easier and cheaper to adapt one of the commercially available control units listed by RSM than to make your own, in case you were thinking of doing that. I know this from personal experience.

 

The Black Talon Concept Chimera FET I believe does away with the need for a cut off lever in that respect.

 

I'm not familiar with BTC fets, but looking at pictures online, it does seem like the Chimera has a button on the trigger board that would interface with the cut off lever. Perhaps a custom trigger board could be made to suit this gearbox? (wouldn't really need to be a board in this case, just some switches wired up the right way)

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hmm. how about having 2 fets, 1 set for full auto only, 1 set for semi only and use a physical switch to dictate which has access to the motor? Somewhat nasty way of doing it.

 

EDIT: Scrap that stupid idea as it won't work without the mechanical switching on the gearbox

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I think the 3D-printed stuff is pretty fragile, but I agree that at least the rear receiver 'looks' like it should be polymer, having taken a few styling cues from MagPul's PDR-D, just as the front looks like it should be an aluminium extrusion, as it resembles Mega Arms' MaTen.

 

I wonder whether having an injection mould made would be that much more expensive than having the whole thing milled out of aluminium...  :wacko:

 

Anyhow, BIGBC, BTC are definitely the people to talk to. The designer posts on here (as Blacktalon) and he might be able to help you integrate his design into your gun in particular and the ACBC in general.

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I wonder whether having an injection mould made would be that much more expensive than having the whole thing milled out of aluminium...  

A whole lot more. A simple mold for injection molding starts at about 5k and that was quoted to me by Armscor. If it's not to be made in a third world country you're looking in the tens of thousands and complex molds that are meant to last go into the hundreds.

 

edit:

A cheaper alternative is to print/sculpt the positive in abs or styrene to make a negative silicone mold and cast the shell out of fiberglass.

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Really? In my head an injection mould is basically a negative of the actual design milled out of stainless steel or something similar, with a few vent holes drilled in, and the item itself but smaller as the 'inner'. Admittedly for this design it looks like a mould would need two clamshell halves and two insert pieces (one for the gearbox, and one for the magazine well) but $10k? Wow.

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Make the rear part from fiberglass, it cost about 2 dozen of dollars, and will be as durable as the aluminium. The molding is useful if you want to make many stocks and sell them.

 

It can be materially painted.

 

If you-re interested take a look of my Bullpup M14, and M14 SE2 projects.

 

In the bullpup topic I posted the wiring plan used ACM wizard for the ergonomic and fully electric trigger/ fire selector...

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Really? In my head an injection mould is basically a negative of the actual design milled out of stainless steel or something similar, with a few vent holes drilled in, and the item itself but smaller as the 'inner'. Admittedly for this design it looks like a mould would need two clamshell halves and two insert pieces (one for the gearbox, and one for the magazine well) but $10k? Wow.

Injection mould design and production is a case of black magic, it's complex and requires a lot of skill and knowledge, not to mention very time consuming. To give you a rough idea, the machine programmer/operator who produces my MP5 SD taclight mounts spent 20 years working as a mould maker and he said it would be 2 - 3 days work to do the whole production (writing programs, setting machines, milling, grinding, finishing, fitting) on a very small steel injection mould for an AEG piston head for me.

 

If you went to a mould maker in the UK to get a mould made for this project I'd be suprised if you got enough change for a pint from £50,000 + VAT, infact I suspect it'd cost quite a lot more.

 

CNC Milling is generally far cheaper and easier to do for a one off or small batches.

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Its already pretty much been answered but -

 

3D printing: not much quicker (saves some time on programming the milling machines but as I am doing this myself its somewhat irrelevant), likely not cheaper on a design of this size, outcome is nice and brittle making it more of a paper-weight than a rifle I could hope to field.

 

Moulding: very much a victim of economies of scale, for single runs/small batches the price per part is hideously expensive. Ive already had to design and produce two mould tools for my course and the time and effort they take makes them largely irrelevant. You have to take into consideration flow planes, cooling patterns, gate locations, shrinkage, draft angles, undercuts and of course - multi-part assembly to actually be able to dissasemble the tool around the moulded part. I would expect making one of the parts + associated tooling would be about as time consuming as just milling the rest of my design out in the first place. 

 

Fiberglass: I had talked this over with my tutor as I have made some masks in a similar way before. There were concerns with the accuracy and finish that could be achieved and the time it would take to do vs milling it out. Seeing as a simple mould or some sacrificial parts would need to be produced first it just seemed like the only real benefit was reduced cost.

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