Rollergun Recoil and the Jerk (not the owner!)

[popgun pete]

“Rollergun” is a generic term which refers to a range of gun types which I have attempted to document in a series of Basic Energy Storage diagrams (Deeper Blue reference, but some are scattered here in various threads).
https://forums.deeperblue.com/thread...agrams.107171/

What a rollergun does is not reduce the recoil to zero, it reduces the jerk which is a technical term for the rate of change of acceleration a. The equation F = m x a can be used to explain this statement (it is actually F = k x m x a, but k = 1 if we use the correct SI units). Any speargun provides maximum force at the beginning of the shot which decreases with the power stroke of the bands, or the air pressure system, to either zero or a cut-off level when it then ceases altogether as the spear leaves the weapon. As the propulsive Force F varies with time t we can express this as dF/dt = d(m x a)/dt = m x da/dt as mass m does not change with time (unless our gun can shoot near the speed of light).

The term da/dt is the jerk and in a band rollergun da/dt is lower as bands don’t simply contract, they reverse direction which requires deceleration and then acceleration as they head in the opposite direction. In a cable gun the bands don’t necessarily reverse direction and only the cables reverse direction going around reciprocating pulley shackles which add drag and some energy losses to the system. I expect that da/dt for a cable gun is also low, plus the gun is slightly underpowered if the doubled or tripled up band battery is not thick enough and that will reduce the jerk.

If you want to check out rollergun recoil then just load your gun and hold it at arm’s length with your wrist twisted to hold the gun across your body perpendicular to the direction that you are facing and then pull the trigger. You will soon find out about recoil!

I maybe should have spelt jerk as "Jerk", here you can read why as it is a proper scientific term:
https://en.wikipedia.org/wiki/Jerk_(physics)

[popgun pete]

Rather than refer to them elsewhere where I may have forgotten, here are the rollergun energy storage diagrams. The diagrams do not go out of date as the laws of Physics don't change.

[popgun pete]

More variations.

[popgun pete]

And more as rollerguns have spawned lots of variations. There are more somewhere as Rollergun 17 to 18 seem to have gone missing, but when I can find them again then I will add them. This stuff is pretty basic as anyone with a Physics or Engineering degree will tell you.

[Behslayer]

Hi Pete, As always you're a Huge resource of information. Is the main difference in Felt Recoil in Rollerguns simple that R = F/T that T is longer? Is there an actual Cancellation of Recoil from bands moving in opposite directions, or is more simply a Longer T in the Recoil = Force/Time?

[popgun pete]

Originally Posted by Behslayer

Hi Pete, As always you're a Huge resource of information. Is the main difference in Felt Recoil in Rollerguns simple that R = F/T that T is longer? Is there an actual Cancellation of Recoil from bands moving in opposite directions, or is more simply a Longer T in the Recoil = Force/Time?

For cancellation you need equal masses at the same velocity, or different masses at different velocities. The bands never leave the gun, but the spear does, so cancellation is not possible. The basic rollergun wraps its bands on the front rollers, unlike a muzzle band anchor there is an interposing band section running back to a rear anchor. This lower band section provides a sort of shock absorber as rubber changing direction and squashing momentarily out of shape on the rollers removes energy from the system and that changes the jerk.

A rollergun usually has the band power of a longer gun shooting a shorter spear, a rollergun is less efficient than a simple band gun, but it can be more effective, which is a different thing to efficiency.

[kodama]

Great that we have people like you around. So much to learn.

I am by no means an expert but after a couple of years of experience with a roller which I tuned and tinkered with. I am moving back to a classic two banded 110. Setup properly it is hard to beat and I just love the simplicity of it all.

But since I am always open to new ideas I might change my mind again at some point.

[popgun pete]

Originally Posted by kodama

Great that we have people like you around. So much to learn.

I am by no means an expert but after a couple of years of experience with a roller which I tuned and tinkered with. I am moving back to a classic two banded 110. Setup properly it is hard to beat and I just love the simplicity of it all.

But since I am always open to new ideas I might change my mind again at some point.

Simplicity shaped the spearguns of the sixties and seventies, lessons learned in the fifties where they tried everything have been forgotten and now we are repeating the exercise and making complicated guns again. Cable rollerguns were tried in the distant past, but they were unreliable and owners were stuck for replacement parts. Head down in the boat fixing their creations their pals were meanwhile shooting up the reef with their “plain vanilla” guns. The only difference today is most of us carry a brace of guns and can heave the problematic gun in the boat and then set off with another weapon.

[2fishin2]

First question....is simplicity measurable? Probably not, more of IMHO

Its a subjective description of "something"

The Alemani type rollers are for sure not in the same category as single banded rollers.

Roller guns in small sizes are shooting 8.5 - 10 mm shafts and killing big fish. I don't know of any 115cm banded gun that can shoot an 8.5mm shaft and kill 100lb fish "responsibly"

There's a big difference between poking a 100lb fish with a 7mm shaft and killing one with an 8.5mm shaft

PP I think you are not being objective enough with the Alemani type guns. Many top spearfishermen have moved to the guns and for good reason. Your research of guns in particular older types is extremely noteworthy. I challenge you to get your hands on the newer Alemani and Carbonia guns and give us more of your research.

There are times and places for both type guns. Small fish sure simple 2-banded classic guns are the go-to choice. Yes I have and use them also.

Inverted rollers use different size band combinations and types depending on their use in the configuration. example would be using a mix of 16 and 18mm reactive bands on the bottom pullys and 16mm more elastic type on kicker bands (if installed)

One point often missed is that with the lack of recoil comes more improved efficiency and accuracy. First time I ever shot one I was astonished at the lack of. At first, I felt the lack of equated to lack of power. My mind was changed when the guns would shoot shafts completely through the hardest headed fish in the ocean the Giant Trevally.

As far as maintenance goes, they are no different than other guns to take care of. Sure they have more bands but tying a roller band and classic is exactly the same.

[popgun pete]

Originally Posted by 2fishin2

First question....is simplicity measurable? Probably not, more of IMHO

Its a subjective description of "something"

The Alemani type rollers are for sure not in the same category as single banded rollers.

Roller guns in small sizes are shooting 8.5 - 10 mm shafts and killing big fish. I don't know of any 115cm banded gun that can shoot an 8.5mm shaft and kill 100lb fish "responsibly"

There's a big difference between poking a 100lb fish with a 7mm shaft and killing one with an 8.5mm shaft

PP I think you are not being objective enough with the Alemani type guns. Many top spearfishermen have moved to the guns and for good reason. Your research of guns in particular older types is extremely noteworthy. I challenge you to get your hands on the newer Alemani and Carbonia guns and give us more of your research.

There are times and places for both type guns. Small fish sure simple 2-banded classic guns are the go-to choice. Yes I have and use them also.

Inverted rollers use different size band combinations and types depending on their use in the configuration. example would be using a mix of 16 and 18mm reactive bands on the bottom pullys and 16mm more elastic type on kicker bands (if installed)

One point often missed is that with the lack of recoil comes more improved efficiency and accuracy. First time I ever shot one I was astonished at the lack of. At first, I felt the lack of equated to lack of power. My mind was changed when the guns would shoot shafts completely through the hardest headed fish in the ocean the Giant Trevally.

As far as maintenance goes, they are no different than other guns to take care of. Sure they have more bands but tying a roller band and classic is exactly the same.

I am not being a cheerleader or critic of one gun with respect to another, in fact my analysis is entirely objective. As for a measure of simplicity the most obvious would be the time to fix a gun in terms of replacing the bands. A simple band gun has the bands changed in a minute, maybe even less. The band loop equalizes side to side and that is it. On band battery rollerguns you need to make sure that the band strands are all the same length or you have side to side pull problems. I have my own rollerguns, but I have closely studied the Alemanni guns and looked at the work of others. A band gun is a simple thing, even a rollergun and the diagrams show all the various types. A rollergun in most of its forms is a folded up band gun, although the band battery guns are not strictly folded, in fact they are stretched out as their bands are short for the length of the gun. The “Arbaparanco” guns were the first of these in terms of a production gun, but gun tinkerers had made their own versions before they appeared.

If you look at rollergun 14 it is a very powerful gun as the pre-stretch which you in a sense throw away as you never use it is the power of rollergun 8. The rollergun 14 uses further up the band stretch gradient to power the gun, but it may eventually kill the bands. The Alemanni design is characterized by using lower stretch to prolong the life of the bands.

Found another diagram!

[gspearguns]

Originally Posted by 2fishin2

First question....is simplicity measurable? Probably not, more of IMHO

Its a subjective description of "something"

The Alemani type rollers are for sure not in the same category as single banded rollers.

Roller guns in small sizes are shooting 8.5 - 10 mm shafts and killing big fish. I don't know of any 115cm banded gun that can shoot an 8.5mm shaft and kill 100lb fish "responsibly"

There's a big difference between poking a 100lb fish with a 7mm shaft and killing one with an 8.5mm shaft

PP I think you are not being objective enough with the Alemani type guns. Many top spearfishermen have moved to the guns and for good reason. Your research of guns in particular older types is extremely noteworthy. I challenge you to get your hands on the newer Alemani and Carbonia guns and give us more of your research.

There are times and places for both type guns. Small fish sure simple 2-banded classic guns are the go-to choice. Yes I have and use them also.

Inverted rollers use different size band combinations and types depending on their use in the configuration. example would be using a mix of 16 and 18mm reactive bands on the bottom pullys and 16mm more elastic type on kicker bands (if installed)

One point often missed is that with the lack of recoil comes more improved efficiency and accuracy. First time I ever shot one I was astonished at the lack of. At first, I felt the lack of equated to lack of power. My mind was changed when the guns would shoot shafts completely through the hardest headed fish in the ocean the Giant Trevally.

As far as maintenance goes, they are no different than other guns to take care of. Sure they have more bands but tying a roller band and classic is exactly the same.

Looking from angle of spearguns builder I think Pete through his diagrams makes understanding of various working principles easy for everyone. For me his analysys is very useful. Working principles of Alemanni and Carbonia are described on his pictures.

[popgun pete]

A band battery gun that I never got around to building is the longer version with two horizontal pulleys stacked vertically in the rear of the cocking stock. These automatically equalize the bands in the band battery on either side of the gun because the bands are continuous side to side. Coaming covers are required to keep your fingers and any line out of the moving band drive otherwise you may run into tangles as lines get sucked into the band drive. The inspiration for this gun goes back to the "Arrow" gun and uses every inch of the gun stock from butt to tip. This cannon is a variation on Rollergun 14 and has a longer cocking stock which you will need to brace against when you pull the trigger. A tensioning mechanism can be used to move the cocking stock or the pulleys rearwards to set up the band pre-tension. This idea is borrowed from the twin grip "Fusil Americain" band gun/rollergun of the forties. (Demande 28 April 1949 by the United Service Agency)

Photo of "Fusil Americain" Rollergun supplied by John Warren, original gun owner Jack Prodanovich, this gun is now lodged in the Museum of Skindiving History created by Ron Mullins. Jack donated the gun to the museum for the education and instruction of the spearfishing fraternity.

[popgun pete]

This is the diagram for Rollergun 14 XTP which like the Alemanni rollerguns uses low stretch factor bands (relatively) and every inch of the gun body for the drive system. Those seeking more power can use a triple band battery instead of a double. or use thicker bands. The rear pulley travel system is not shown, but uses a hydraulic telescoping stock to apply some of the prestretch (blue band), the rest has to be built in and the bands released in storage. The hydraulic rearwards stock shifter is the last loading action before shooting. After the shot the hydraulic stock has to be released for reloading thus allowing the rear horizontal pulleys to move forwards and enabling the cable wishbone to be drawn back on the top deck.

Proportions of the gun shown are for illustrative purposes and are not prescriptive.

[popgun pete]

I am moving this post here where it really belongs.

On band wrapped muzzle rollers you have mode 1 propulsion from the top deck band run and mode 2 propulsion from the band run on the lower deck. Mode 1 propulsion is the same as standard band gun propulsion, i.e. no rollers. For a very light shaft mode 1 propulsion will heave the shaft from the gun before mode 2 gets going. For heavy shafts mode 1 and mode 2 work together as the band drive segments transition from mode 1 to mode 2. At the same time the axle load falls from the cocked to shoot state as band tension reduces as the bands continue to contract. Less pressure on the roller axle and the squeeze films collapse, however by that time the shaft is well underway. During the shot some band storage energy is consumed in bending and distorting the bands around the curvature of the rollers, this creates some inefficiency, but also a shock absorber effect by resisting the acceleration of the bands as they do a U-turn around the rollers which in itself is an acceleration, a centripetal acceleration. When you cocked the gun the energy for this centripetal acceleration and band shape distortion was supplied by your loading effort, but it was never stored in the bands, so it then has to be supplied by the energy stored in the bands during the shot which over a band soak period starts to ebb away until an equilibrium is reached. Thus all band guns perform better shot sooner rather than later. An exception, if we ever get to see it, is the "Dreamair" cable gun which has no bands and no rollers, but works like a high speed aircraft carrier launching catapult, only it is not steam powered, being a compressed air captive storage weapon.

On cable rollerguns where bands don't go around rollers the braking effect of squashing and reversing the bands does not take place, so those losses don't occur. However the bands are now shorter than they should be for the gun's overall length, so without doubling up the band battery the gun is underpowered. Also there is an energy cost in pulling rearwards the side shackle pulleys through the water which is not present in a standard band wrapping rollergun. The band ends and the side shackle pulleys move through half the length of the wishbone draw on the gun's top deck as there is a two to one relationship due to the cable being wrapped on the side shackles and the cable thus doubling up on itself. One method of lengthening the bands is to install the rear band anchors on another and larger set of rollers at the rear of the gun with the bands now anchoring at a point forward of these rear rollers in an inverted arrangement, however this does not change the stroke length of the side-shackle pulleys. What it does allow is the bands to be pre-tensioned instead and the gun now shoots further up on the band stretch gradient, something not possible before with limited length available on the gun body for the band accommodation.

However the bands now once more undergo being squashed and wound back on themselves, only here at the rear end of the gun, but forward of the grip handle, the distortion and losses are much lower as the curvature of the rear set of rollers is much larger than the muzzle wrapped rollers on a standard rollergun. This type of inverted double pulley rollergun is much less energy efficient as it incurs more parasitic losses than a standard rollergun does, but can be made more powerful by using significant pre-stretch without pulling the guts out of the now longer bands.

Another approach would be to mount the rear set of large rollers at the rear of the gun on a vertical axle behind the grip handle and wrap the bands in a big U-turn from one side of the gun to the other, however the band drive would need side shields to keep one’s fingers and the shooting line out of the moving band drive.

Delayed responses and cable drag reduce the jerk of these gun as all the extra parts need to be accelerated and moved through the water, unlike a plain vanilla band gun, but the gun is shooting a much shorter spear as once again the gun’s drive train had been folded, only this time at the rear end of the gun. The advantage of a vertical rear axle roller set is the band battery equalizes in length on either side of the gun as the band strands are connected rather than being separate rubber strands on each side of the gun body. This gun set-up is shown in Rollergun 14 XTP, an extended propulsion drive battery using all the length of the gun from butt to muzzle.

An early rollergun using this vertical pulley axle arrangement was the twin handle “Fusil Americain” which looks much like a spring gun, but is in fact a band powered rollergun with an impeller drive unit operating in the top slotted barrel that guides the impeller. This heavy and complex gun had four shooting powers and lever handle supercharging which puts many of our later efforts in the shade, but the gun cost a fortune and very few were made and of course it sinks like a stone whether loaded or not. An additional benefit of the design was the gun could be operated as a mid or rear handle with trigger mechanism lockouts on either set of handles by using the safety button on each grip to either block the trigger or lock it in the fired position. This gun was a product of the "USA", the UNITED SERVICE AGENCY created by Alexandre Kramarenko and his associate Charles Henry Wilen who produced the first spring gun ever in 1937. Charles Henry Wilen was an American like Guy Gilpatric living on the French Riviera at the start of spearfishing using mechanical weapons and much of this was described in Gilpatric's "Compleat Goggler" book derived from four years of Saturday Evening Post articles. Make sure you read it before you die as then everything falls into place. Hans Hass got started by being fascinated when seeing a man diving and spearing fish from his vantage point on shore, that man was Guy Gilpatric! Thus the wheel of history turns and what seemed to be disparate links all click into place.

[spearq8]

I think many people should realize that not all roller guns are the same and this might be the reason why some people just hate them and others really like them. They absolutely do not shoot the same and setup is much more difficult than with a classic setup. There are two basic types of roller guns ... the normal roller gun using just a simple roller that is in the muzzle and allows you to increase the contraction stroke distance of the band and thus you can theoretically pack more energy than with a normal classic band due to the longer power stroke ... or of course due to the fact that you can pre-stretch the band. And of course the invert roller which uses pulleys on the bottom and thus allows you to pack energy with less effort + the fact that with an invert, the roller is dealing with the rotation of a cable (much less diameter than a rubber band) so losses via the roller are much less. Plus the invert roller gives you a much cleaner sight picture as the bands are below line of sight. Obviously due to that fact you can pack more band energy from below without affecting sight picture on top. Of course there is a limitation to all that, which is the Terminal Velocity of the shaft. The lighter the shaft the more likely that you will reach the Terminal Velocity of the shaft quicker. So it makes no sense to go for a very complicated invert roller system if you are shooting a 130cm 6.5mm shaft ... most likely you would be able to reach the TV of that shaft with just 2 x 14mm bands ... so packing all the energy in the world into that setup will not help and if anything it will hurt performance. So to take advantage of the extra packed energy you would have to increase the mass of the shaft to 8mm or even higher. This is something that a classic gun cannot compete with. Shorter more compact guns that are shooting heavy shafts. I can already see that with say an 8mm shaft at around 150cm ... 2 x 14.5 mm bands ... even with 380% band stretch and 130cm of stretch ... they just can't push the shaft fast enough to get a nice flat trajectory and for sure a properly built invert roller should give you better performance than a classic setup. But add a 3rd band on the classic setup and things even out again but then that is a setup not many people want for an 8mm shaft. Now once you get to longer band strokes of 140cm or 150cm stretch and 3 hot classic bands ... you reach the point where even an 8.5mm shaft is very close to TV and I have yet to see even the best invert roller improve on the performance of that. So it would make no sense to go with a complicated roller setup for that type of setup.

If you can be objective about all this data you can make a better decision on what best suits your needs. Of course I am comparing properly designed classic guns to against properly designed roller guns. A classic gun design is pretty easy to setup and you can get a lot of information on how to do that properly. With a roller, it is a lot more complicated and I dare say that 90% of roller guns out there are improperly designed or improperly setup (that is being conservative). With a roller gun, it is a LOT more difficult to get the shaft out of the track stable, and if you don't stabilize the shaft then the gun is going to shoot like crap.