Basic Rollergun Energy Storage Diagrams

seatrophy said:

Hi i did some practical research about differ type roller guns and conventional spear gun ... i'd wrote an article about it, and maybe this will be useful
LINK TO READ ARTICLE

by the way.. i agree with you that the inverted roller type is are bad idea ..bat not only the inverted roller is a good way to waste energy time and money..

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When I clicked on your link my virus alert put up a "Who don't go there!", so you better check for viruses or malware on that site! Also I never said that inverted rollers are a bad idea, it is just that they are energy inefficient. Plenty of spearguns are energy inefficient, but if you have enough energy stored in the gun that you can throw some away then no big problem. My multi-band guns are very inefficient as stretched rubber is a poor energy store, however approximately 90% of spearguns have poor efficiency and yet have harvested lots of fish which is what it is all about.

seatrophy said:

i know about that virus alert issue but i cannot resolve it ..f%ckin Ucoz hoster put in every free sites like advert ..
i talk with hoster support service and they said:they did that kinda advert for free sites
if i knew it before i never choose this free hoster but now it too late.. the only way it just close the pop up window with virus alert advert and watch the site page normally

regarding to the rest of you message ) you can believe to my research or not, or can try to make the same testing platform and play with it )
and you well see the truth about roller guns any type
on my test inverted roller with the same conditions shooting just on 75-80% of power than can do classical one band roller gun or two band conventional speargun

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I suggest that you create a new thread here as no one with a virus alert is going to click on your existing page as getting rid of malware is a pain in the butt.

Just did this diagram for another forum, but thought that I would add it here as well. This "Briante" cable rollergun is very similar to the “Alemanni” demultiplied cable rollerguns, but has a few quirky features of its own such as no trigger finger guard, that job being partly served by the upper rear of the horizontal mount drum reel.



The last photo shows the optional top deck or "kicker band", note that its anchor point is set back from the muzzle as its function is to jerk the cable rollergun into action. Whether the gun really needs it is open to opinion, but it will add to the gun's energy storage.

Some rollerguns which are of the band wrapping type In terms of the band going around a roller use a connecting link in some of the bands so that they can branch out into two bands. This means that at one end the band has the wishbone and at the other or rear end there are two anchor points, or four if you count the other two for the paired band on the other side of the gunthat forms that particular band group. You can see these linked or composite bands on the Alemmani "Bluewater Express" which is a double rollergun. The composite bands are indicated by red markers and use the outer set of muzzle rollers on the gun. The central band group is of the top and bottom deck window pulley wrapping type where the bands pass through a window in the stock that contains pulleys or rollers. Thus these bands have their anchor on the top deck forward on the gun body and their run to the muzzle on the bottom deck via the windows in the stock. The Alemmani "Vela 135" also has such bands, but there they are part of a cable rollergun where the front end of the bands are connected to a moving shackle set of rollers which the long cable wishbone passes around and then runs forward to the muzzle rollers which are sized for cable, not rubber.

The composite bands are there to aid loading as the bands can be cocked by drawing the wishbone back with one of the rear anchors engaged and the other one free. The gun can then be flipped over and the second anchor engaged by pulling the second band pair back. In the "Bluewater Express" the rear band pairs are a wraparound band and a tied end band which is essentially a short wishbone to hook over the rear anchor point, this being a pulley mounted in a horizontal drum fashion just in front of the trigger finger guard. In the above diagram we can see the rear anchor B for the composite bands and the forward anchor A for the window wrapping band set. Note that window wrapping band sets are always under prestretch as they are used to operate further up the band stretch gradient of that band set in order to harvest more force from the bands while still having enough real estate on the gun body to occupy, otherwise they would never fit on the gun.


Make up of Composite Bands: Here we will just consider one side of the gun. If the bands were just rubber with no limiting cords inside them then at a node where two bands join onto one band the force each side has to be the same as the node does not move when the gun is cocked. If the two bands on the bifurcated side are at 200% elongation then the force is doubled (as there are two bands) and if the band they are joined onto is of the same diameter then it bears the force that it will produce at 400% elongation which would be too much for it. The limiting cord inside the single band can be sized to stop the band at 200% elongation after which it in effect becomes simply a connecting cable. Taking that cable length you calculate the lengths from the node at the front cable stretched back to the rear anchors. Those lengths will be the stretched lengths, hence if the rear bands are at 200% elongation then those lengths need to be one third of that when you cut the bands to size, allowing for the node length and the wishbone length.

When the gun shoots the bands give up their energy in the sections, so you add up the work energy triangles, not the forces as the contributions from each band are not constant over the wishbone draw length. This is demonstrated by the use of those green triangles on the rollergun Work Energy diagrams. Here I used 200% elongation and the same rubber diameter, but the logic is the same whatever you scale it up to.

Here is another Alemanni rollergun, the "Carbon Stilo Express 115" that uses composite bands on what is a double rollergun. Note that this is a rollergun and not a cable rollergun as the muzzle rollers are sized for stretched rubber. This gun basically uses up all available space on the bottom deck of the gun to stow the bands before they are cocked for shooting. Cocking requires two wishbone draws followed by the setting of the second set of bands of the outer composite bands on the mid anchor point on the gun. For some reason there is a connecting link on the central or inner band group that may be there to attach an optional set of bands in a piggy back fashion to create another rear band set for anchoring on the mid anchor provided by the larger of the two drums.

It now appears that the aim of the design is to create composite bands where the forward section of each band group is slightly narrower than the rear section so that they are less likely to create drag when the front end of the gun is traversed, hence they want a low profile presented by the stretched bands after the gun is cocked. This is not always the case as can be seen by this rollergun which has bands that are of the same diameter from end to end. These rollerguns have a certain amount of stretch applied to the bands to fit them onto the gun, so that will push the force levels higher up the band stretch gradient when the gun is cocked. In long term storage the bands need to be removed or the rubber under tension will crack as oxygen in the air attacks stressed rubber.

Although not a speargun the rollerspear uses a roller to wrap a band that is longer than would normally be fitted to a polespear or hand spear. This allows a longer stretch length for increased energy storage in the weapon. Not a new idea as rollerspears go back to 1939 with Commander Yves Le Prieur's rollerspear patent. Note that the bands used in those early days were sourced from other applications, such as motor vehicle elastics, and for the rollerspear are of a square cross section tied on with cord whipping.

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Just revisiting the Briante B3 "Pacific" there is another band group on that gun as seen here.

Adding the contribution of band group 2 makes the energy storage closer to that of a 2 band standard gun using similar bands.

Work or Energy not being a vector we can just add the contributions up in terms of the areas represented by the green graphs, hence the areas can be turned around or stacked in sections as it is the magnitude that counts, not the shape of the graphs. In terms of actual forces we would have a big triangle, the rectangular depiction is simply to make area comparisons easier.

This diagram demonstrates why rollergun muzzles have to bear double the loading of a standard band gun muzzle.

This sketch shows the rollergun at 300% stretch in the medium position (neglecting cord lengths which have to be included otherwise as they take up some on the band run length on the gun).

I purchased one of Seal's (Kosta Kanarov) rollerguns which was one of three new guns that he had completed before he was tragically lost on a spearfishing trip when he was caught in a downward current in a treacherous diving area of interconnected reefs and submarine canyons. Despite the efforts of his dive buddies who searched for him all day right through to sunset he was never found, although his personal gun was recovered as he had taken a shot at something.

This gun is an inverted rollergun of 130 cm with a 3 band battery, the main band set are a top and bottom deck band run which are always hooked up (except when in storage) and a double piggyback set that are loaded on the rear anchors after the wishbone is set on the shaft tab or wishbone notch. The gun is extremely well-made with attention to every detail.



Here is a diagram for it, although this particular Seal inverted rollergun only has one piggyback band, not two.

A couple more diagrams showing the forces that try to tilt a gun when it shoots.

You can see from this sequence that even an inverted rollergun (cable rollergun) has some recoil as attested by the movement of the hand during this shot. Spear shaft is 10 mm diameter which is a heavy projectile for spearfishing.

The images with lines added for shaft and gun axes show the relative motions between the B1 and B2 photos which are stills from a video.


Note while the gun moves backwards and tilts on the operator's hand, the spear remains on much the same trajectory as shown by the white lines. Gun movement is shown by the red lines.

As a matter of interest check out the energy storage of a seven band “standard” gun, which would be a ballasted mid-handle, with an inverted rollergun. The mighty jerk created when pulling the trigger on the former gun requires an enclosed track and a very heavy and bulky gun body to stabilize the shot. Such a monster is for Bluewater action only.

Briante creates a gold leaf covered rollergun for the spearfisherman who has everything (well maybe not everything).

Oreste Vacondio is well known for his development work on rollerguns, but I was never able to look at his speargun patents until now. Over the years more historic patents have appeared as the job of scanning them is gradually completed and they get uploaded to databases where they can be found on searches provided that they are correctly classified.

This patent from March 2007 shows a system for varying the power of a band gun. A fitting that can be moved along the barrel that the bands can easily pass through can catch the band ferrules which are of a larger diameter, they being provided with a shock absorbing element to absorb the impact. This idea carried through to his rollergun design where a similar element incorporated at the muzzle acted as a wishbone stopper. The wishbone is pulled up and the shaft tab slides free without being flipped up by the wishbone. The sliding and locking fitting on the barrel tube then becomes a variable position band anchor whereby you can vary the power of the rollergun by locking it off at various positions.



The second patent from February 2010 is basically the idea for a sub-pulley or “demultiplied” rollergun which is now a much more familiar item these days than when it was when first introduced. The block and tackle nature of this arrangement is noted on the diagrams and made a cable rollergun a reality that actually worked.

Another rollergun type is the "Fusion" which is a hybrid of the other rollergun types and is distinguished by having a short set of bands which remain on the gun’s top deck and which are connected to the end of the drive cables that wrap the muzzle rollers. That means the bands do not travel around the muzzle rollers at any time, most of the propulsion being derived from the bands on the bottom deck. If the bands top and bottom are the same rubber type and size then the upper set don’t have to be stretch limited, but if the lower bands are thicker or in multiple sets with a bifurcated connection to the drive cable then the top bands need an inner cord to stop them being over stretched. Being stretch limited they add nothing to cocked gun cable tension until the spear is released at which time the top band set can start to contract. The diagram below compares a standard rollergun (if there is such a thing) to the simplest form of a Fusion rollergun.