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Basic Rollergun Energy Storage Diagrams

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popgun pete

Well-Known Member
Jul 30, 2008
These rollergun diagrams are scattered in forums across the Web, but I thought that if consolidated here they may be more useful, especially when some are now "buried" in disparate threads and are thus hard to find; unless you already know that they are there!
rollergun 1, with std gun.jpg
rollergun 1A, with std gun.jpg
rollergun 2, with preload or cocking lever.jpg
rollergun 3, preload std phantom.jpg
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Another variation spotted by spearq8 on "Spearboard". A 3 times pulley reduction system!!, but the gun looks good and very nice attention to detail. I have not modeled the other simple roller band wishbone yet, but you can see that band pre-load is vital to providing some grunt when using a three strand cable run as each strand takes one third of the tension. A "block and tackle" hoisting system, but used in reverse!
Scorpio Deathstalker 6.jpg

rollergun 14, twin cable gun CXR.jpg

Scorpio Deathstalker 5.jpg
Here is a "Wiggler" band system used to cram more slack band length in a much shorter linear space on the stock. The "zig-zags" allow the band length to be approximately doubled, but it will depend on the amplitude of the wiggler rollers' vertical spacing. The "Wiggler" band storage sits under enclosing side shields open at the bottom for water to drain out. It is likely that band (and maybe cable passage) through the "Wiggler" labyrinth will gobble up any energy storage gains, but this system avoids secondary moving pulleys splitting and thereby reducing tension going into the wishbone, i.e. no "block and tackle" effect. The arming lever is a ratchet device, not an over-the-centre lever.
rollergun 20, wiggler.jpg
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The "Alemanni" rollerguns are a variation on the sub-pulley theme, this is their long range shooter, the Vela 135 Special. As this gun is presented on the "Alemanni" website in plan views (top and bottom) and side elevation we don't need a sketch to show how it works in storing energy.
vela 135 travel lengths BR.jpg

Note that this cable rollergun has five band groups, but the first four are the bands that perform the propulsion stroke on the spear. Band group 5 is a short band applied to steady the shaft in the gun, then the single wishbone that connects to the other band groups is pulled back to the desired shaft tab position. The moving sub-pulley system halves the tension of the bands going into that wishbone, hence it will be easier to cock than it may at first appear. The stretch factor is low on the bands if you compare the slack (yellow) and elongation (red) lengths, with only one group, band group 2, having any preload (blue) which is shown here only as an estimate, being the longest band group on the gun.
vela 135 3 views XX.jpg
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Thank you Pete. This is exactly what I have been looking for. I saw one of these "de multiplied" guns for the first time a few weeks ago when a spearo brought one out to the Coral Sea with him. He was confident with it, & certainly competent as he landed a few tuna with it. I was impressed & curious enough that I'm going to be laying up a couple of blanks tomorrow to start playing around with pulleys. I have never liked roller guns, but these are something very different & offer a real advantage IMO. It was a bit of a eureka moment as the doubling of the draw from the pulleys also overcomes the problem I have been carrying around in my head for a couple of decades around the use of eccentrics. In order to get a reasonable draw length out of eccentrics, they need to be large, now using pulleys to double the draw they dont have to be so big. I wont be putting eccentrics with pulleys just yet, but the concept of a compound speargun is getting closer. In order to have a fair comparison with my current tuna guns these experiments will be 1.5m from muzzle to trigger & use a 6ft 3/8 spear. Even an increase in range of 1m would be of value to me.
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vela 135 comparison RR.jpg
Here is the Band Energy Storage Diagram for the Alemanni "Vela 135 Special" Cable Gun (its derivation is shown below).
vela 135 special energy RR.gif
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Thanks Pete. I am not going to use the conventional rubber on these practice runs, just four rubbers through the pulleys. I want to see for myself the potential of this concept & if it works then add it to a couple of eccentrics to make a true compound speargun. It may not work, but it may, & I'm sure I'll learn a couple of things in the process. Here is a couple of blanks I glued up over the weekend. That is one of my large four rubber guns to their right for a comparison of length ( have I told everyone how much I love load assists!). Hopefully next weekend I can get back to them for shaping & the handles & butts. With luck these may get wet before the new year.
Maybe you could try a "Wiggler" design as band group 2 on the Alemanni "Vela 135 Special" does this by spreading itself over top and bottom decks before loading. If I was designing the Alemanni for more power then I would put two "band group 2" bands on the gun in tandem, not one as is used now. Also being wide and flat a "wiggler band battery" could snake laterally rather than vertically on such a wide bodied gun.
vela 135 top XKD.jpg
I'm really just doing them as prototypes to get my head around the potential value. I want to give the concept every opportunity to impress, before making any real judgement & dont want to muddy or confound the outcomes by hybridising concepts yet. I've seen one of these de multiplied guns work, & it worked well & the owner was confident & successful with it. By no means are these guns I'm currently building going to be the basis of my own quiver, it is just trial & error ATM & all I am hoping is they may provide the gateway to a true compound speargun, one with true eccentrics, not rollers, which reverse the energy cycle. If i am happy the next step is to install eccentrics somewhere, I havent decided on their position yet, will they be horizontal or in sheave boxes, or if I will have one or two pairs, if I do go ahead with the prototype. What I do know is the rubbers will be as short as 40mm & the draw length will come grom the eccentrics rolling over & the gain due to the ratio of the pulleys. The eureka moment for me was using the weakness from pulleys & eccentrics individually to actually compliment each other. The current guns should be working by the new year & if I am still excited then the next generation several weeks later.
Bear in mind that the "Vela 135 Special" is maybe less special when you cast it in a different light as shown here.
vela 135 vs 4 band gunRR.jpg

The low stretch bands make it less powerful than a four band gun using the same rubber band type. In order to lift performance it requires more band pre-tension or shorter bands than it uses now. On the top deck the shaft is accelerated for longer, but with half the force levels as shown in the previous diagram where the green graph is long and thin (the middle graph at the bottom of that diagram)..
Its going to be interesting to compare a couple of these to similar sized standard rubber guns, I'll also make them avaliable to the folks in the local clubs to try & for them to form an opinion on too. For myself, an extra meter of range on tuna would be awesome from a gun, but the reduced recoil, if it is true would also be a bonus. Sometimes I find myself forcing equalisation, especially after a few straight days of diving, I get myself into trouble sometimes when using two hands on the big guns instead of using one to equalise at depth, at this point I am still sinking & it has ruptured my ears on a few occasions. I know a couple of extremely talented & experienced divers who cant or wont use a big gun for this reason, it costs them opportunities on big fish. Shooting a 6' x 3/8 spear with one hand isnt something to be overlooked. I just see these demultiplied guns as a bit of fun ATM, but also a step to the next thing, which I think could be a true compound speargun.
There is a better alternative which does not use the "demultiplier" system. This is a rollergun, not a cable gun.
Oceanic Bluewater Express 3 views.jpg
Not interested in any roller guns, particularly when it comes to big guns. Seen lots & none have offered anything to make me want to swap a three or four rubber mid handled gun for one. On a recent tuna trip a couple of divers turned up with expensive long double roller guns, at first they were selling their virtues & by the end of the trip I felt sorry for them because of how badly handy capped they had been & they knew it too. All I want from the guns I'm working on ATM is an insight into their practicality & to see if it is worth putting eccentrics after very short rubbers & before the pulleys.
The only speargun that I have seen mimic a compound bow's "let-off" at max draw was the "Sea Archer". The attached diagram shows the cam's operation on the power band.
Sea Archer cam action.gif

There used to be an article on the web showing exactly how it all worked as it was in a sense a type of sling device, it having no holding trigger mechanism, instead the user fired it somewhat like a bow and arrow, hence its "Sea Archer" name.

Sea Archer Front.jpg
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