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Old 01-10-2018, 01:18 PM   #1
artiz
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The Return of the Aluminium Speargun


I have been working on this concept gun for many years now and I'm finally nearing completion. I've worked through the 3D printing route so that I can easily create my own highly detailed lost wax castes for aluminium smelting rather than the more expensive 'tooling' option... that may come later after/if I get a decent proof of concept... and obviously field testing it out here in SE Asia where I'm now living.
I have obviously not thought of everything and probably made some glaring mistakes so your feedback and thoughts will be very much appreciated.



You can also view the 3D model in Sketchfab using the link below.
Inverted Aluminium Speargun Prototype - Loaded by artiz on Sketchfab

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Old 01-10-2018, 04:53 PM   #2
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Re: The Return of the Aluminium Speargun

Looks fantastic, keep going!

Would be interested to see how it performed in different lengths, which would be easy, just change out the barrel!

Well done brother, well done.
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Old 01-10-2018, 05:18 PM   #3
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Re: The Return of the Aluminium Speargun

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Looks fantastic, keep going!

Would be interested to see how it performed in different lengths, which would be easy, just change out the barrel!

Well done brother, well done.
Much thanks Will.. hope all is good for you mate! I added the line wrap points to the head design so that different barrel lengths could be more easily managed. I've been tied up with travelling and work for just a bit too long so its been nice getting back to my real passion here in Thailand over the last few weeks. May just make my way down through Indonesia to Bali this year if all goes well. Next stop Australia for 2019 even... fingers crossed!
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Old 01-10-2018, 06:07 PM   #4
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Re: The Return of the Aluminium Speargun

Neat. Looks complicated w/ lots of entanglement options. How the hell do you cock it and what keeps those lines from coming off the rollers when the tension is relieved?
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Old 01-10-2018, 07:27 PM   #5
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Re: The Return of the Aluminium Speargun

it looks cool to see a speargun all layed out in a motion graphic like that but I see a few potential issues.
For one - if it is all aluminum - it will be way too heavy and just sink- especially in a rear handle like that - you won't be able to hold it out in front of you .
I would make as much of the gun from delrin and carbon fiber as possible to lose some weight.
- the old aluminum tube guns - used paper thin aluminum tubes- with thick enough tubes to allow an air pocket to add buoyancy.

With a roller gun - you want a heavy spear to get the power out of the thing- and using a heavy spear will make a heavy gun even heavier.



The design DOES look cool - and you SHOULD make the darn thing - just be careful it's not too crazy heavy.

Beautiful pictures- definitely
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Old 01-11-2018, 02:31 AM   #6
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Re: The Return of the Aluminium Speargun

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Neat. Looks complicated w/ lots of entanglement options. How the hell do you cock it and what keeps those lines from coming off the rollers when the tension is relieved?

All the testing I did with my 3D printed versions proved pretty much tangle free... it was always a major concern and seeing as I have now upped the tangling options with this version it will continue to be an issue. I can only do so much whilst still at the design stage though... as you point out tangle hell is most probably waiting for me... time will tell.
I also did an unloaded Sketchfab model if you are interested. The rigging is never actually fully loosened... it remains constantly under slight tension even when not loaded.


Cocking the gun is exactly what the extra pulleys are all about...


The more pulleys used automatically makes loading that much easier as you can see from the Force/Load block & tackle graphic above... or put another way... more power for your pull. This new design takes advantage of the set up seen in number 4 above which reduces your exertion to cock/load by three quarters and equates to the gun being 75% more powerful when no pullies are used pulling the same load... as in length/thickness of rubbers. Meaning in real terms that you have a hell of a lot of extra power to play with whilst cocking/loading is that much easier. The resulting options for rigging are therefore pretty much endless... rubber thickness/length etc... as is optimum barrel and spear length of course. If you don't actually need to swing around an unwieldy row boat oar when you are down there... why would you? The other issue this design deals with is the double/triple cocking set ups... who needs a gun you have to load twice/thrice FFS... no thanks. At the same time having the rubbers stretching in opposite directions mostly eliminates kick or recoil allowing a far smoother spear release which delivers the much desired potential for an even more constantly accurate gun.
That's the theory anyway and it certainly worked with my 2 pulley 3D printed prototypes so onwards and upwards.

Thanks for your input Marcus... hope all is well with you mate!
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Old 01-11-2018, 03:30 AM   #7
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Re: The Return of the Aluminium Speargun

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Originally Posted by triponempa View Post
it looks cool to see a speargun all layed out in a motion graphic like that but I see a few potential issues.
For one - if it is all aluminum - it will be way too heavy and just sink- especially in a rear handle like that - you won't be able to hold it out in front of you .
I would make as much of the gun from delrin and carbon fiber as possible to lose some weight.
- the old aluminum tube guns - used paper thin aluminum tubes- with thick enough tubes to allow an air pocket to add buoyancy.

With a roller gun - you want a heavy spear to get the power out of the thing- and using a heavy spear will make a heavy gun even heavier.

The design DOES look cool - and you SHOULD make the darn thing - just be careful it's not too crazy heavy.

Beautiful pictures- definitely
Thanks for your feedback... yes neutral/slight bouyancy will very much figure in the eventual success of this design.
The optimum wall thickness will probably come later on in the final design process. Having designed professionally for Delphi in the past I'm reasonably familiar with most aluminium extrusion design issues and yet it can be very tough going. I'm yet to delve into the interior of this current design prototype but it's pretty much next on the agenda. You can actually have a look inside my design in the Sketchfab model... just 'mouse wheel' your way inside and have a look around.








The strength, beauty and durability of aluminium are all key here for me though... I've done plastic & carbon... now I want to make the real thing... a polished aluminium speargun which may last me for the rest of my life... and perhaps even my sons too... you never know.

Again much thanks for your comments!
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Old 01-11-2018, 08:02 AM   #8
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Re: The Return of the Aluminium Speargun

Ah, you've definitely have done your homework. I understand block n tackle. That means you're going to have to pull an inordinate amount in order to get the desired stretch of the band.
So, you attach the line to the spear notch...but then what do you grab and pull to cock it?
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Old 01-11-2018, 09:54 AM   #9
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Re: The Return of the Aluminium Speargun

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So, you attach the line to the spear notch...but then what do you grab and pull to cock it?
You'll need to take those shades off indoors Marcus... you grasp the black handle attached to the red line! The blue line is the spear line.
Actually I can see you getting confused regarding the images I've posted because there's a few different configurations with double wishbones and extra rubbers on top... I should have explained that.


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Originally Posted by Marcus View Post
That means you're going to have to pull an inordinate amount in order to get the desired stretch of the band.
This is a very good point though... and where my 3D printed prototypes really proved their worth. What I found was that I could counter the longer final pull with both the length/thickness of the bands combined with the preloading tension of the set up. In effect it's already half-ish or more loaded before the final cock/load. Getting the balance spot on was a little tricky at first but once I'd got it correct the harnessed power really was impressive... even from my little 50cm cave and gully gun which has a range of around 4 meters. Another benefit is how much you save when buying top quality band of course.

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Old 01-11-2018, 03:45 PM   #10
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Re: The Return of the Aluminium Speargun

very cool. not 100% sure I understand what is going on here. Mulitples of pulleys allows an easier load but requires a longer pull? I can lift 100lbs 6' with one pulley and it will feel like 100lbs and require 6' of pull. two pulleys it will feel like 50lbs and require 12' of pull, etc.. Like your drawing above. To raise the weight 10cm requires 100N at 10cm pull. To lessen the load to 25N, requires 4 pulleys and 40cm of pull. I guess that's where I'm getting lost here.. Where is the extra rope? also, the extra pulleys increase the friction? might this Geared Sheave be an option? I went through some talks at the Harken Office with people who understand pulleys better than me.. I was looking for the Holy Grail. Loading a Large Force easily in one stage.. answer was there. Force Multipliers using stacks of Pulleys, but required long lines.. I thought to find a compromise by using a Geared Sheave.. but it was like a dog chasing it's tail..

What is interesting is stacking loads, like a multiple band Inverted system. I like the Internal Band concept. I'm just unclear about the physics with all of these pulleys.

very cool. awesome to have skilled engineers sharing on here.
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Old 01-11-2018, 04:01 PM   #11
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Re: The Return of the Aluminium Speargun

Artiz,

Something isn't jiving here.

(Work) Distance of pull x Force in = the same amount of work out - friction. How is this any different from a simple band gun if you're pulling the same distance with the same amount of force?
I do see one advantage in that you'll already be a bit preloaded and the pull will stretch a much shorter stiffer band that could give you more of a work input due to a more flat force input across the stretch, whereas pulling a simple band starts off easy then gets harder towards the end.
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Old 01-11-2018, 07:33 PM   #12
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Re: The Return of the Aluminium Speargun

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Artiz,

Something isn't jiving here.

(Work) Distance of pull x Force in = the same amount of work out - friction. How is this any different from a simple band gun if you're pulling the same distance with the same amount of force?
I do see one advantage in that you'll already be a bit preloaded and the pull will stretch a much shorter stiffer band that could give you more of a work input due to a more flat force input across the stretch, whereas pulling a simple band starts off easy then gets harder towards the end.
Yup. Put another way, the bands will deliver a bit more energy to the shaft since they won't become fully relaxed due to the preload. RG's aren't magic- it's still about band modulus times stretch, just as you and Jon indicated. They don't deliver more energy, but they do shoot softer due to the longer, slower acceleration. I'm like you guys- I don't see this gun as being more powerful. That said, it's a really interesting project and looks like it will result in a very flexible, beautiful looking gun that will last a lifetime if given proper care.

Like others, I can't wail to see some buoyancy calcs, which should be pretty easy with the 3d cad. It will be hard to get a gun that short to neutral buoyancy with all the solid aluminum hardware.
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Old 01-11-2018, 07:35 PM   #13
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Re: The Return of the Aluminium Speargun

Looked through the unloaded model. Still wondering. Is this a single stage loading? Are you pulling on the top Loading loop one time and using the stacked pulleys to be able to load a more powerful charge? But then you don't get the distance of pull? One thing that might be interesting is using some kind of ratchet. Loading that internal band set to hook into the upper band. then loading the Upper band. Basically like a standard inverter. Two step loading. I figure if you could power up significantly and use a lighter shaft a Geared Sheave might get over any loss to friction. I'm still not sure I understand what you are doing here. Maybe Popgun Pete will make one of his Energy transfer diagrams.
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Old 01-12-2018, 12:10 AM   #14
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Re: The Return of the Aluminium Speargun

Probably better if I answer you all at the same time.

Firstly... let's get this out of the way *'MORE POWERFUL'* is definitely not what these inversion style set ups are about. The ability to fine tune/manipulate/play with peak force and how the kinetic energy is applied to the projectile/shaft however most definitely is. Pulley (inversion) systems therefore allow you to do just that... and the pulley systems with line rather than bands alone clearly reduce drag and friction to a minimum whilst costing much less. No magical powers there then! Put simply: more 'power' to play 'with' rather than just simply *'MORE POWERFUL'*. Apologies for not explaining that from the beginning but believe me it's not that easy to find the right words.
Secondly... elimination/reduction of recoil, kick, flick or whatever you want to call it is one of the real 'holy grails'... how smoothly/efficiently can I get my spear to leave the gun and what can I manipulate to achieve that... with a standard gun nothing... with a standard roller gun it's still mostly nothing... with an inversion/pulley style set up it's more than I've worked out myself... or probably ever will!
So what is 'going on here' is that I'm 'opening a can of worms' and then pouring them into 'muddy waters'!
I'm most certainly not going to take any credit at all for this stuff either... far more proficient/smart engineers have written about these complex dynamics right across the internet if you care to read. However this bloke is 'Boss' for me...

FINAL VERDICT: Roller guns provide greater work for less peak force than a conventional gun, allowing reduced recoil for a given shaft kinetic energy. This is the findings of the physics involved. Whether or not this is worth it depends greatly on the setup, and there will be a point of diminishing returns where reducing recoil adds little to no value.


His technical explanation (click the link above) of the physics involved here is second to none!

So with the use of the 4 pulley system I am attempting to neutralise the recoil with opposing forces but with just one final easier cock/load using that all important pretension... and yet I may well now be on the path to the 'point of diminishing returns'... again time will tell... and yet again if that is the case I still have the options in place to return to my tried and tested 2 pulley system. One last thing... don't actually make the mistake of thinking I know exactly what I'm talking about here.

Finally... for me it really is all about the final 'tweaked' set up and the extent of the resulting possibilities... design, graphics and Youtube can only help so much... the finished gun will tell all... no harm in trying is there?

Once again much thanks for your time guys... your feedback really is invaluable... the more you question the more I have to think about exactly what I'm trying to achieve here.
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Old 01-12-2018, 08:18 AM   #15
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Re: The Return of the Aluminium Speargun

Ah, that makes a bit more sense.

Beh,
I liked your idea of a two stage cock with a ratchet isolator. Although complex, it could possibly be made durable.
Obstacle: Couldn't use a ratchet roller with a half turn of line around it. Line would just slip. You'd need multiple wraps for friction.
Another approach would be to attach second stage directly to spear attach line such that ~half way thru the pull the second stage took over.

That got me wheels spinnin' a bit more. Using the same type of concept, why couldn't it be designed such that the first pull stage was of a lower modulus and the second pull stage of a higher modulus thus creating more of a constant force that prevents shaft whip?
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