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Old 11-29-2016, 04:11 PM   #1
popgun pete
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Rollergun Recoil and the Jerk (not the owner!)

“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)

Last edited by popgun pete; 11-29-2016 at 05:40 PM. Reason: add reference
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Old 12-23-2018, 08:30 PM   #2
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Re: Rollergun Recoil and the Jerk (not the owner!)

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.
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Old 12-23-2018, 08:37 PM   #3
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Re: Rollergun Recoil and the Jerk (not the owner!)

More variations.
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Old 12-23-2018, 08:46 PM   #4
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Re: Rollergun Recoil and the Jerk (not the owner!)

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.
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Last edited by popgun pete; 12-23-2018 at 08:54 PM.
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Old 12-24-2018, 01:18 AM   #5
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Re: Rollergun Recoil and the Jerk (not the owner!)

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?
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Old 12-24-2018, 01:32 AM   #6
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Re: Rollergun Recoil and the Jerk (not the owner!)

Quote:
Originally Posted by Behslayer View Post
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.
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Old 12-24-2018, 05:46 AM   #7
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Rollergun Recoil and the Jerk (not the owner!)

Quote:
Originally Posted by popgun pete View Post
.

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.


For clarity sake how do you define effectiveness and efficiency in this context ?
Thanks for the diagrams by the way.

Last edited by kodama; 12-24-2018 at 11:08 AM.
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Old 12-24-2018, 08:00 AM   #8
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Re: Rollergun Recoil and the Jerk (not the owner!)

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Originally Posted by kodama View Post
For clarity sake how do you define effectiveness and efficiency in this contey?
Thanks for the diagrams by the way.
High efficiency is where the effort to load the gun, which requires a certain amount of work or energy, is all translated into spear propulsion, in other words little energy is lost. No spearguns ever return 100% as there are always losses, but the most efficient guns are probably the pneumovacuum gun and the pistonless gun principally due to low frictional losses in both types. However if you were going to shoot a big Tuna and stop it in its tracks with a lethal hit then you would not use a pneumatic, instead you would use a multi-band cannon that could hurl a heavy large diameter shaft at considerable velocity. Such a cannon is very inefficient, as most band guns are due to the use of rubber as an energy storage medium, but they are very effective. If you were loading and shooting a gun all day then a very efficient gun would be your choice as you only have a limited amount of loading effort and eventually get tired, but nobody does that, so efficiency is not such a big concern.

If you were in tight places or an obstructed environment and snap shooting skittish fish “on the wing“ then a small pneumovacuum gun like a Russian “Taimen” would be ideal as it makes the most use of a limited amount of energy in a small gun package which is very manoeuvrable. Not surprising as that is exactly what it was designed for.

Spearguns need to be matched to the quarry and the capabilities of the user, no point is swimming around with a gun that you cannot load maybe more than a couple of times, or will send shafts clean though all your targets and then bury the tip in the reef structure.

Rollerguns have more losses than simple band guns due to more moving parts that all take energy to move which does not then get used for spear propulsion.

Last edited by popgun pete; 12-24-2018 at 08:15 AM.
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Old 12-24-2018, 08:24 AM   #9
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Re: Rollergun Recoil and the Jerk (not the owner!)

Setting all the "T"s, "R"s, and "F"s off to the side for a moment.

Lord know's I've used more than my fair share of spearguns....

My favorite and go to gun was always an Aimrite carbon 120. However, I have learned to like the inverted/fusion rollers.

Right now my favorite gun to shoot has become a Roisub Fusion in 115 size. Have full confidence in shooting anything up to 100lbs or so.

I have an Alemani Demultiplied 120 that I have not had the opportunity to shoot yet. 2019 for sure.

I have my eyes set on a Carbonia 115 to pick up after the first of the year. I really like how they have integrated all the components "into" the gun.

"Inverted/Fusion" rollers allow you to shoot larger fish at more range than comparable sized band guns. Shorter guns with larger diameter shafts are definately a better all around gun.

I do still have an Abellan Albacore for clear water big fish but for the time being, I am really liking the inverted roller type guns.


Have you guys seen that Alemani has made a take down gun? Sweet!

https://www.alemanni-sub.com/en/prod...120-travel-pro
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Old 12-24-2018, 10:59 AM   #10
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Re: Rollergun Recoil and the Jerk (not the owner!)

Quote:
Originally Posted by popgun pete View Post
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.
for powering of roller gun I have seen guys using either a 3 pairs of rubber ,2 small connecting by SS Ring plus another one will be loaded later or a single roller with a classic band slot its like combination ,is this enough to cover the band power loss ?roller gun look nice but I don't like the end kick once the band reach to the pulleys still it shoot accurate may be because the spear left the muzzle before that kick .
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Old 12-24-2018, 11:18 AM   #11
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Re: Rollergun Recoil and the Jerk (not the owner!)

Quote:
Originally Posted by 2fishin2 View Post



I have my eyes set on a Carbonia 115 to pick up after the first of the year. I really like how they have integrated all the components "into" the gun.





https://www.alemanni-sub.com/en/prod...120-travel-pro

Would love to see a review about the Carbonia!! They have been on my radar since day one. Pricey but it seems like they figured out and combined the most effective setup I can think of.
Please share your experiences once you have shot it.
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Old 12-24-2018, 01:00 PM   #12
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Re: Rollergun Recoil and the Jerk (not the owner!)

There are no miracles in rollerguns, that was the purpose of the diagrams to show that any of them can be broken down to their equivalents shown on those diagrams. Names like “Fusion” just confuse the overall picture as rollerguns fall broadly into two types, cable rollerguns and wrapped band rollerguns. If you have full draw cable wishbones that run the full length of the top deck then to fit rubber on the gun you have to use a side-pulley system as that has half the travel of the wishbone draw on the top deck. No miracle there as a moving side-pulley uses doubled up cable and that is why you have a 2:1 drive, but you then halve the power in the band battery. The gun body has to withstand double the compressive forces that the gun shoots with as the roller axle faces double the loading that a simple muzzle anchor slot has to cope with as you have forces acting above and below the connections running to the rollers.

The Wiggler system is a way to accommodate a length of band in a shorter linear length on the gun body by zig-zagging it around secondary rollers and then you can go back to a 1:1 drive for the wishbone and bands, however there will be losses with bands distorting and winding around those additional rollers.

Some guns like the Alemanni models use a mix of types and conventional helper bands as well, but these guns are rather inefficient and are not quickly repaired or re-banded.

Rollerguns have been around almost as long as spearfishing, including rack cocking and lever operation loading such as this Bellan model gun which as shown here moves the band anchor forwards, but in another embodiment discussed in the patent reverses the rack system and uses bands wrapped around rollers at the muzzle.

In 40 plus years of spearfishing I have shot nearly everything except a Tapmatic SMG and a carbon dioxide gun. Worst guns would be the spring guns as they are very inefficient as the buckling spring under compression rubs on the barrel tube.
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Last edited by popgun pete; 12-25-2018 at 12:17 AM.
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Old 12-24-2018, 02:23 PM   #13
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Re: Rollergun Recoil and the Jerk (not the owner!)

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.
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Old 12-24-2018, 05:02 PM   #14
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Re: Rollergun Recoil and the Jerk (not the owner!)

Quote:
Originally Posted by kodama View Post
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.
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Old 12-25-2018, 12:12 AM   #15
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Re: Rollergun Recoil and the Jerk (not the owner!)

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.
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