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GeckoSub Mirage Evo - And Adventures in 3D Printing Speargun Parts

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.
I thought I was clear about the propose of attached mathematical calculation..? The result of calculation is the initial speed and the energy of the shaft. I thought some of you understood what I was talking about..? Calculated initial speed of the shaft is very close to the actual initial speed of the shaft in water. I've already confirmed that measuring the speed of the shaft in water, years ago. Just to remind you I also had measured the speed of the shaft on different distances and using different lines and sliders: https://forums.deeperblue.com/threads/different-setups-performance.91753/
 
It does not tell you anything unless the increase in cocked pressure is not being realized in the results which would indicate that something was amiss, such as internal breathing (throttling effects) or a tight section in the barrel bore slowing the piston down. These factors are not being modeled so the mathematics is not really of any use. In early “Sten” guns if you tightened up the inlet valve body then the brass half rings that held the power regulator block pulled tight into the annular barrel groove and slightly necked down the inner barrel bore, but no amount of modelling would predict that happening. Water outlet from a wet barrel gun can be affected by the relief ports flow. On some older guns it was possible to screw the inner barrel further into the muzzle and partly close off the rear part of the ports as the barrel was not held far enough back in the rear handle due to the inlet valve body not being fully screwed in and this moved the inner barrel forwards in the gun. However the trigger transmission pin was still able to push the sear lever, but only just.as the mechanism slot was long enough in the bottom of the inner barrel.
 
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Pete, you were right!
Calculation is really not of any use - on maybe 5 % of pneumatic spearguns, especially if they were bad design of bad maintenance and assembly.
But calculation is applicable on 95 % of other nowadays pneumatic spearguns where there were no throttling issues or poor barrel manufacturing or bad assembly.
 
Reactions: Zahar and Diving Gecko

I don't mind the exercise at all. Like Tomi says, we have to make some allowances and say most spearguns are pretty much equally efficient.
Over the past few years, a handful of guys in the bandgun world are beginning to be able to make what seems to be pretty good rules of thumb on how a certain mass of spear needs a certain combination of bands (power) - if the guns are pretty decently designed without major flaws that is.
I was thinking that perhaps in a few years, with more experience, testing and knowledge sharing perhaps we would reach a point where we could make some similarly general pointers in terms of what levels of energy would be needed for a certain mass of shaft.
But I would need to make the guns, test them and hunt with them first to get the data - so the data gathering and correlating it with any formulas would just be an added bonus to the fun of building and shooting the guns.
 
tromic said:
Davide, just keep going on with nice projets like this one...
Click to expand...

I will!
Just not sure when. I may be relocating to another country this year, so that would set my DIY projects back quite a bit.

One of the things I really like about building or modifying a gun and then taking it on a long trip is the conclusions I can make afterwards. Of course, I like the fish and the ocean, too no doubt - but time spent in the water firms up my thoughts so that I have a better direction for the next project.
Right now, I have a pretty good idea on how I'd like a medium sized tuna gun to look and what power I am after. Let's see when I can get around to actually building it.
 
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I can not actually remember if I had seen your GeckoSub Mirage Evo rigging and the shaft/spear setup. Have you used your Dima titanium slider with it?
I suppose it is pretty hydrodynamic.. What do you think what would be the shooting like if it were a real free shaft on 22 bar? (I mean without a line - just a spear). Would it still be sluggish?
 

I'm using 1.7mm stiff dyneema on one of the shafts and 1.4mm cable on the other. And yes to Dima's small sliders. Can't really say what it would be like without any rigging as I've never tried that.


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And what was your target distance, I suppose more than 6 m?
Here is a reminder how much the thickness of the line effects the performance of shooting.
(Results in table were obtained by measurement in water - not calculation using mathematical model)
The black nylon rope was original Mares line with Cyrano speargun. I suppose it is most similar to your 1.7 mm dyneema..
https://forums.deeperblue.com/threads/different-setups-performance.91753/#post-854032
Of course I understand you can not change the thickness of the line for your prey and the only way to improve the performance is to increase the pressure and the thickness of the shaft so the momentum (v * m) would be higher .
 
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The tail pushing axial drive, completely enclosed barrel and oil lubricated trigger mechanism make the pneumatic gun less prone to shooting accuracy problems compared with bandguns. Also the centralizing muzzle washer or stop ring provides two control points on the shaft minimizing any shaft bending under rapid loading as the shaft tail is firmly gripped by the piston which itself is under control by the inner barrel tube. The bandgun is a slingshot or catapult whereas the pneumatic and hydropneumatic are true guns. Being pressure driven their propulsion is infinitely variable with any pressure increment available right up to the gun's maximum operating pressure, provided that you can load it. The supreme embodiment of this system are the hydropumping annular piston guns which unfortunately do not float after the shot unless enclosed in a bulky jacket, because a pump handle allows the gun to reach maximum power and shaft velocity of any speargun. The downside is if the gun explodes you are finished if you are holding it at the time.

There are pneumatic guns which do not have a piston controlling their spear tails and they are the muzzle sealed forward latching guns and the hydropneumatic guns using a similar layout. One such muzzle sealed gun that defies all convention is the tail latching hydropneumatic RPS-3 which holds the title of the most unlikely and intriguing speargun ever built and also one of the most inefficient as the inner barrel porting was not optimized for the job.
 
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How I originally came across the hydropneumatic guns was I was thinking about how to make a “Mirage” type gun with a lever operated mechanical advantage pump. It was obvious that the “Mirage” was designed to have an air pump that utilized the spear as the pump rod as that was the simplest way to do it. However the disadvantage was you were loading from the front end via the muzzle and I wanted to work from the rear of the gun as that is much safer if the gun unexpectedly shoots. One way to reverse the pump pushing direction was to use water as a push element that could do a U-turn in the gun and I thought that if there were already spring guns and pneumatic guns were there ever any “hydraulic spearguns” and that is what I searched on and up came the "Aquatech" company in the Ukraine. Now way back then in 2000 the website was all in Russian and with no free on-line translators in Russian I used a Russian to English dictionary to translate most of it. That is how I found out about hydropneumatic guns and more importantly the hydropumping guns with an auxiliary hydropump. First thing was I needed to see how the basic gun worked so I ordered the Aquatech 500A model hydropneumatic as at that size I had a good chance of getting it through Customs. After that the rest is history as I then suggested to Sergiy, who owned the "Aquatech" business, to build a hydropumping gun which became the “Black Sea" gun as in their country that is really the only place where a big gun could be used. After test shots in the Dnieper River we needed a guinea pig who was brave enough to pull the trigger on a BIG Tuna in the open ocean and up came Fernando Abella. Various Tuna were shot, Fernando nearly knocked himself out with the recoil and the gun had to be salvaged by a deep diving team after he dropped it. So that is how the rear lever pumped hydropneumatic gun in that long form came to be.

The photos below are of the first "Black Sea" gun built for and used by Fernando Abella to see if it could shoot Tuna and the answer was that it could because of its enormous shooting power!



However it seemed that although not as straightforward as the hydropneumatic, a pumping gun could be done as a pneumatic and I designed but never finished a triple concentric tank gun where it combined a pneumatic gun with a hydraulic pump, the hydraulic pump being used as a direction changer for the air pump as deep down the layout was still like the “Mirage”, but the pump was external and worked from the back end of the gun to drive an air pump inside the gun.
 
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Reactions: Diving Gecko
Wow. Had no clue. But yes, once one has fiddled around with a Mirage a lever pump does seem like a natural progression.
My thoughts are on placing it externally, too but right in front of the handle in a recess in what would be the tummy of a more bulbous reservoir.
I'll probably stick to a pneumatic pump only, though.


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The main problem with the "Mirage" is its poor airflow, which DG has largely eliminated, and now we know that although not perfect parts can be fabricated and tested in plastic which was not something ever done before. The "Mirage Evo" made with permanent injection molding dies could be a production gun within a short period, but the next step would be to move the pump to a position where it could be done from the rear. Unlike the hydropumped hydropneumatc guns where the last pump stroke is hard, in the "Mirage" it is very easy, so the design has to make that first pump easier in the pneumatic gun, especially if it has 40 bar plus in it!
 
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Normally I would greet new members to the board - especially our little section of it. But since the above was your very first post on the whole of the forum, allow me to ask you to elaborate a bit more on your endeavors in spearfishing and 3d printed parts?

The thing is, the link you posted is a crap collection of pseudo reviews. From a quick glance, it looks to be just another site phishing for clicks. We have had a few incidents like these and the admins are very good at get rid of stuff like this.

Apologies, if I'm mistaken - but let me hear your thoughts on why I am not.


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Perhaps he would know more if he, i.e. smithnovel, read this thread from the very beginning rather than just the last page as his post seems to infer.
 
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I looked around online and found you on a few 3d printing and CAD forums. In one place, within the last few weeks, you mention that you are brand new to 3D printing, in another you say you offer 3D printing services and in this one you say you have been printing for "the last few years"...
Furthermore, on a forum for biomedical 3d printing you happen to do the exact same thing you did in my thread; you say you have experience with the subject matter, though it is pretty clear you just latch onto one simple piece of info in the thread at hand and then propose that the viewers go look for generic info at that website of yours. Like when you say you have done "nose cones projects" and "had issues in our process".

My thinking now is that you are a human 'bot trying to direct traffic to a website where it just so happens that you have a lot "reviews" (in brackets because they aren't more than a comparison of specs) of products with direct links to Amazon. So, I guess you are looking to cash in on the Amazon Affiliate kickbacks.

This forum has amazing admins and one thing we don't like is spam. So, why don't you share some pics of the nose cones you supposedly made...?
 
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Reactions: popgun pete and Zahar
Good background checking and it seems that the post was, as you say, a website pointer to something of no real consequence.
 
3D-Printed Line Releases
Found a bit of time to try to alleviate one of my main gripes with the Cyrano handle which is the crappy line release. As mentioned earlier it definitely cost me fish as the metal trigger rubbing on the metal line release creates way too much friction with tight line wraps.
So, I had a go at printing some plastic line releases - I could also have gone for a plastic trigger and kept the metal line release:


Since the original ones are rather thick in places (6mm), I could beef up the plastic ones so they may actually hold up. I modelled some after original but made the plastic version slightly longer and also made some without the "cut out" for the resetting spring. I actually find the resetting spring unnecessarily strong so may not use it and in that case I can use the beefier line releases.

It was a fairly easy to draw these up as I used a flatbed scanner to scan the original line release, then imported the image into Fusion 360 and traced the shape:




I think you can make out the overlaid scan on top of "my part" here:


I am in Thailand these days and a friend of mine was gifted an Ender 3 Pro printer and it really is a nice bit of kit for the price. Out of the box it prints quite well and the frame is way stiffer than my Anycubic I3 Mega and I think the printer is a whole lot quieter. I still feel, since I spent a few weeks really calibrating mine and dialing in the filaments that I get slightly better quality from mine, but I have no doubt that I could get to the same level on this one. If I was in the market right now for a sturdy, well thought out cheap printer, I think this is the one. And the flexible magnetic bed is almost addictive.



Oh! Judging from feel, they work a whole lot better than the SS one. So, if they don't break, it was worth the afternoon I spent on this project
 
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Reactions: landshark sa and Nico66
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