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'Compound' Spring Powered Speargun (concept)

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artiz

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Compound Speargun sml.jpg

I've had a little experience of DIY crossbows from younger years but have retained enough of an interest to stay up to date and in particular with some recent compound developments. Burri a Swiss crossbow maker recently came up with this monster below... which does actually look more suitable for a speargun design... bar the telescopic sights and obvious weight. Those double springs would be very difficult to get the balance right though so I've gone for a single.


I've been messing around with this DIY idea for a while and happened to read a post from Sharkey... a DB member... who mentioned the possible benefits of a Compound Speargun... being the smooth and increasing distribution of power through the projectile rather than the instantaneous 'hit' and recoil of our band guns.
I'd therefore really appreciate any advice/thoughts/perceived negatives etc from any of you experienced gun builders out there... it is clearly a madcap idea presently but I would still like to have a go at building one... if its possible/feasible of course!
Thanks in advance!

 
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Apneaddict

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Go for it!!

I'm not a builder, but I appreciate all things mechanical.

All I'm thinking initially is rust potential of the spring, overall buoyancy, balance (front-to-back) and maneuverability in a current / when tracking (but the mid-handle design somewhat negates that).

Also, a long shaft stores a lot of energy when moving fast, which is critical when moving through water (as opposed to air) and then a fish. Those short arrows / darts wouldn't cut it in H2O and the tips would likely need to be smaller.
 
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artiz

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Go for it!!

I'm not a builder, but I appreciate all things mechanical.

All I'm thinking initially is rust potential of the spring, overall buoyancy, balance (front-to-back) and maneuverability in a current / when tracking (but the mid-handle design somewhat negates that).

Also, a long shaft stores a lot of energy when moving fast, which is critical when moving through water (as opposed to air) and then a fish. Those short arrows / darts wouldn't cut it in H2O and the tips would likely need to be smaller.
I'm thinking Aluminium for metal parts (being easier to work and lighter of course) and a cheapish spring which could be easily changed out when maintenace fails... better still plastic covered perhaps ... not that sure about hard wood either but again more convenient to work with of course... Carbon Fibre would be first choice but probably too expensive for me.
Although it may appear a bit like a pistol in my graphics the dimensions of my 3D model are 1.1M long with a 90cm spear... but they are just guess work/general at this stage. The other benefits of this design would be the ability to use a slimmer spear shaft... less wobble given the even dynamics of the power source... perhaps easier to load too.

Thanks for your encouragement Apneaddict!
 

sharkey

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Nov 22, 2013
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That looks surprisingly familiar in design to something I built many years ago. Though in a speargun not a cross bow of course.

I think if someone is going to build a roller gun then they might as well just build a compound speargun. The advantages of going that little bit further would be worth it IMO.

I'd suggest putting the cams & the springs/rubber/etc behind a mid handle & just using a very short pull ( larger cams will increase the draw length if you want to go that way). There will be less drag in the water because the "barrel" only supports the spear & holds the shooting line, it doesn't have to support the power off the bands, so can be much thinner & lighter. Spears won't have to be as stiff/ thick, as the power thrust is reversed & the spears start slowly then increase in speed, not starting at top power & going down in energy as with our traditional design.

Looking forward to seeing some getting built & used.

Sharkey
 
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sharkey

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I'm thinking Aluminium for metal parts (being easier to work and lighter of course) and a cheapish spring which could be easily changed out when maintenace fails... better still plastic covered perhaps ... not that sure about hard wood either but again more convenient to work with of course... Carbon Fibre would be first choice but probably too expensive for me.
Although it may appear a bit like a pistol in my graphics the dimensions of my 3D model are 1.1M long with a 90cm spear... but they are just guess work/general at this stage. The other benefits of this design would be the ability to use a slimmer spear shaft... less wobble given the even dynamics of the power source... perhaps easier to load too.

Thanks for your encouragement Apneaddict!

I used the eccentrics from a standard compound bow. These should be easy & cheap to source in different sizes (get the largest to try first), & I'd strongly recommend you stay with round eccentrics, not the ones which act more like "cams". The cams will give more "let off" & power but they are also more difficult to tune.

Sharkey
 
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artiz

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That looks surprisingly familiar in design to something I built many years ago. Though in a speargun not a cross bow of course.

I think if someone is going to build a roller gun then they might as well just build a compound speargun. The advantages of going that little bit further would be worth it IMO.

I'd suggest putting the cams & the springs/rubber/etc behind a mid handle & just using a very short pull ( larger cams will increase the draw length if you want to go that way). There will be less drag in the water because the "barrel" only supports the spear & holds the shooting line, it doesn't have to support the power off the bands, so can be much thinner & lighter. Spears won't have to be as stiff/ thick, as the power thrust is reversed & the spears start slowly then increase in speed, not starting at top power & going down in energy as with our traditional design.

Looking forward to seeing some getting built & used.

Sharkey
I used the eccentrics from a standard compound bow. These should be easy & cheap to source in different sizes (get the largest to try first), & I'd strongly recommend you stay with round eccentrics, not the ones which act more like "cams". The cams will give more "let off" & power but they are also more difficult to tune.

Sharkey
I was hoping you could give some advice Sharkey... much thanks... not so easy to get 'compound' parts in the UK so it may be difficult to find ready made... I like the idea of making/putting together as much of it myself anyway and I'm definitely not in a rush. I'm assuming that the placement of my arms/cams/pullies/gun length/handle etc will be drawn out through doing a proof of concept and plenty of prototypes... but I will of course keep your suggestions in mind... much thanks again!
 
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foxfish

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Good luck, I am always up for trying out unusual things...
I think the main problems would be overall bulk, underwater balance & cost but a cool idea all the same...
 
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artiz

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Thanks for your comments so far but I think what I was also actually asking... does it look OK/good/silly/impractical/user unfriendly etc?
Design wise I prefer the look of the Burri (photo above) but then again the need for a single spring was key for the first attempt. Personally I still don't like the arms and would prefer the full pully system that Burri uses above... overall I'm thinking my initial design is kind of 'ugly'?
I was also looking at Spaghetti's thread regarding all the different Italian roller/pully configurations... all been done before by the looks of it... but still with bands as the power source.
Sharky... I'm beginning to understand the benefits of a shorter crossbow pull and your thinking that the basic set up of an underwater compound crossbow seems more suitable than a traditional rubber band sling?.. and did you consider hollow or machined aluminium in any of your designs/ideas? The ability to order 3D printed aluminium spearguns could be very attractive?

Back to the drawing board!
 
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foxfish

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To be honest I really cant think of a more impractical design, I cant see the benefit for my type of fishing!
I like a very slim muzzle with a good tracking ability's & perfect balance... as does virtually every UK spearo.
Perhaps for blue water spearing where more power & less manoeuvrability is required?

The gun that is missing from my perspective would be a pneumatic with a slim barrel mounted on top of a reservoir ... like the very popular pre charged air riffles design.
 
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artiz

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I like a very slim muzzle with a good tracking ability's & perfect balance... as does virtually every UK spearo.
Perhaps for blue water spearing where more power & less manoeuvrability is required?
Agreed... its clearly the idea of a smoother more even power release that is attractive rather than getting 'more power' than I need... I'll come back a few steps first... simplicity perhaps... I've got an old donor gun with a working trigger mechanism so I'm going to begin there instead.
DIY simplicity (below) definitely appeals to me but it's often not until you 'show off' your 'grand plan' that it actually looks wrong...

 
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artiz

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slimmed down compound speargun 2 sml.jpg


Slimmed down, loaded and aluminium... component design could be 3D printed... at least it's looking a bit better than the first medievel attempt... I've also taken your advice Sharkey and shortened the pull which lends itself to a shorter spear.


P.S. Credit where credit is due... this spring/'compound' configuration was first designed by Robert van House in 1977


 
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artiz

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tube compound loaded strings.jpg

Use what you've got DIY variation. You could use any old euro style band gun... I can see problems with fixing the compound parts to a 1mm thick ally tube as well as water ingress of course... open would be better but then you lose your guns buoyancy? Still a bit bulky too. You could also use a band rather than a spring for power... the overriding aim being to avoid the source of power and recoil coming from the front tip of the gun... which in turn hopes to improve accuracy and a smoother release of the spear... and yet not with the delay associated with some roller guns!

 

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I've grown weary of the configuration difficulties involved with the compound aspect of the design. The vital components which I can't make myself more or less dictate the end design. In practical terms its just too complex for me. Even the original inventor van House had problems where to locate the pulleys and arms throughout the life of his crossbow... I haven't totally given up on it but 'pipe dream' comes to mind. So 'component' style roller gun it is. Can someone explain the principles of the 'inverted' aspect please. Not sure what is actually being inverted on the guns I've looked at online?
Latest '007' design attempt...

roller gun.png


The design gun length at the moment is 85cm but the shorter the better as far as I'm personally concerned... waving a 90 around doesn't do it for me in white water, caves/gullies and overhangs... no such thing as 'blue water' when I rock hop... apnea is a thing of the past these days... a one off personalised 'retirement' gun that I can pack in a rucksack is clearly the plan... so the barrel will need to be shortened.
Thoughts behind the 'component' style are based mainly on travel, as are the dimensions. The practicality of lugging around a long barrel and spear in/tied to a rucksack doesn't make any sense. A handle/trigger and muzzle which fit Rob Allen guns maybe the way to go. I could then just buy a longer barrel and spear where/when it's convenient/cost effective/necessary... so it's the egotism of the personalised handle and shortened barrel (not too short) which I'll focus on now...
 
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Broseidon

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Awesome thread! Have really enjoyed looking at all of these - the 3D models are great - I'm not sure many have stopped to appreciate actually how skilled and time consuming those designs must have been. Even though they'll never see the light of day, they're damn impressive.

I like the roller design - nice and simple - just a thought, for your first go, have you thought of using a pre-made handle with trigger mech - surely that would make life a lot easier? A custom handle seems a lot of work!

I'd love to turn my old RA into a roller - it's completely pointless as it's a great gun but it seems like a fun project - maybe one day!

Are you going to buy a pre-made roller kit or try and make one from scratch?
 
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artiz

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Much thanks Broseidon... you have spotted the superflous underbelly of my design attempts... but it is the egotistical desire for a one off personalised self build gun which clearly interests me. I have done a bit of DIY aluminium 'lost wax' casting from recycled ally in the past... which is extremely satisfying... a hollow cast of my own gloved hand will be part of the eventual custom design... particularly as I have an old injury to my trigger finger. I've also got access to a high tech metal lab so another good reason for going the aluminium way.
Having now realised that I don't posses the skills to make a trigger mech or muzzle means I'll buy both... the engineering skills of companies like MVD are just superb anyway. I'll buy/save up for my Rob Allen fitting/dimension parts first and then adjust my design measurements to suit... so kind of self build but no pretensions to reinventing the wheel. Just going through the design process is critically enlightening and why contributions from you blokes here are absolutely essential... so much thanks to all of you.
It's very enjoyable too of course.
 
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artiz

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When I get the trigger mech I can get the precise fitting dimensions and measurements of the hole I need to make in the aluminium handle by using the 3D software to print out... to scale... paper templates! Beginning to look pretty complex though.
How do you blokes go about doing this with your wooden guns?

trigger mech fitting visible.png

trigger mech fitting hidden.png
 
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foxfish

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Your 3 d pics are impressive if not a bit daunting for me!
I cant even imagine building such a complex design in ally!
I think the most important factor with my gun designs are .. being individual but obtaining a perfect balance with a low recoil.
I have never worked with detailed plans however I mainly work with wood so the shape can be added to or mass removed to get a nice shape with good balance in the water.
My concern with alloy would be corrosion, obtaining balance & the overall difficulty of working with metal.
So far I can see some nice drawings but, I also see a very difficult build ahead for you ...
 
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artiz

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Your 3 d pics are impressive if not a bit daunting for me!
I cant even imagine building such a complex design in ally!
I think the most important factor with my gun designs are .. being individual but obtaining a perfect balance with a low recoil.
I have never worked with detailed plans however I mainly work with wood so the shape can be added to or mass removed to get a nice shape with good balance in the water.
My concern with alloy would be corrosion, obtaining balance & the overall difficulty of working with metal.
So far I can see some nice drawings but, I also see a very difficult build ahead for you ...
Maybe time to come clean I suppose... my initial DIY ambition has begun to wane and as I've progressed/faltered through the design bit, it has become crystal clear that my 007 desires are becoming more and more beyond my skill set... so its probably more a case of 'putting it together' rather than self build now... the 3D prototype printing option is ideal in a choice of polycarbonate or alumide (50% aluminium powder and 50% polycarbonate), aluminium and even titanium (below) for the wealthy.

I can design what I want... send off the file and then get it back ready and made in less than a week... not for the traditional gun builder I suppose... but all those beautiful hard wood trees being cut down around the world and all... it seems like a reasonable option for someone with my lust for a custom built speargun without the skill set to match. Cost is falling rapidly too.


Solid Concepts 3D printed Pistol
Personally I can't use a big gun either... so something small and accurate... with a reasonable range of 3-5 meters would be fine... the alumide option (50% lower tensile strength than ally and 50% higher than polycarbonate... which most guns are made of)... is looking promising for the first prototype and then perhaps the full monty... an Aluminium AlSi10Mg version (which is purported not to corrode) when money allows.

It may even be possible to design the hollow elements (voids) to gain a premade neutrally buyount gun based on it's own weight/displacement and the weight of all the component parts to be fitted... and maybe not of course. A new RA barrel is only 25 euros too so my only real concern is the custom cast handle and then getting the dimensions right in my 3D design... jobs a good un! :)
 
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-Paddy-

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Interesting thread lads. 3D modeling is a very powerful tool indeed. I start all my ideas with modeling first. Most of them never see the day light, but it is always good fun.
I have recently modified my RA speargun. I came across RoiSub spearguns which impressed me a lot and decided to build something similar just to see if it really is that good. It works perfect. The accuracy is improved a lot and the range too.
It looks like a complicated system, but is actually easier to operate.
 

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artiz

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Interesting thread lads. 3D modeling is a very powerful tool indeed. I start all my ideas with modeling first. Most of them never see the day light, but it is always good fun.
I have recently modified my RA speargun. I came across RoiSub spearguns which impressed me a lot and decided to build something similar just to see if it really is that good. It works perfect. The accuracy is improved a lot and the range too.
It looks like a complicated system, but is actually easier to operate.
Phwoar... great stuff Paddy... love your rigging... did you make that roller muzzle yourself... and what about that very nice trigger mech on FB... I'm not a member of FB and I don't like using it... so can you tell us more please...
 
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