Roller spearguns

Yes, agreed, I was referring to the one that hurts your wrists more.

Now that's this is ten pages I think I can derail it.

I don't know anyone that takes a double band gun and makes it into a roller with the same diameter band. Usually they go the next size up say 18mm or 20mm. And i'm pretty sure the debate lies in the fact that a roller gun is better than a single band gun.

Did you have an MVD roller on freedive store? I'm interested in two for my two single band rob allens

Quote from Dan

My premise is that personal anecdotes are just that, but physics don't lie. If you take a roller speargun powered as described above and turn it on its side, you'll see the same exact configuration as the conventional speargun, with one band stacked on top of the other. More so the bottom anchoring point doesn't always reach quite as far back as the last tab on the shaft, so band stretch is actually less. The pulley being the only differentiating factor, are divers supposed to believe that it somehow magically amplifies the stored energy of the bands?!

For the comparison that you are citing here the rollergun does not store more energy as shown in the diagrams below. So you are right, there is no magic in adding a pulley (single axle) to the gun. While the stored energy may always be more than a single band conventional gun it will always be less than a double band conventional gun for the same band stretch being used and thus the same F max on all guns.

popgun pete--Thanks for taking the time for your clarifying post.

Next--am I wrong to suggest that THE most correct method to MEASURE spear performance is by MEASURING true flight spear speed?
example-- if spear A exits a roller gun at 300 feet per second (fps) and the SAME spear exits a conventional gun at 305fps, isn't the conventional gun outperforming the roller?
IMO, spear penetration is a product of spear speed AND spear weight. Therefore, SAME spear flying from a gun producing a higher fps number would have greater penetration.

Quote from popgun pete

For the comparison that you are citing here the rollergun does not store more energy as shown in the diagrams below. So you are right, there is no magic in adding a pulley (single axle) to the gun. While the stored energy may always be more than a single band conventional gun it will always be less than a double band conventional gun for the same band stretch being used and thus the same F max on all guns.

The idea of the puleys is to break the speed limit of normal bands.Every shaft has a limit that can be accselerated to with normal bands.Even if you store five time more energy in multi bands configuration,you will give to the shaft only a small part of it,the rest will go for recoil and drag.
The idea of the pulleys and rollers generally is to aply a reasonable pack of energy to the shaft and get high velosity with minimum losses.
I cant understand how people still wonder and dont understand that.Its so simple and we prooved it thousand times.'Its completely same relation between compound bows and classic bows.I came home from the US with a compound bow and can say that it is ten times better than the recurve.

Here is a competition between simple pipe guns again

http://www.youtube.com/watch?v=WXwho2ZjRz0

Dan, you are correct in saying that a single pulley does not create a mechanical advantage, and only changes the direction of the force. What it does allow for is shortening the gun by placing the relaxed band under the gun.

Seal Im not sure what you are describing in your post could you clarify?

Pete. Your diagram is correct if you assume that a single band gun and a single axle roller produce a the same force. By adding a second band you are then doubling the force being applied to the shaft. However Dan, and I both started with the assumption that the rubber on a double band speargun was equivalent to the rubber on a single axle roller. In this case they are both producing similar force at the shaft and as your diagram and my calculations show the roller would be superior. The easiest way to confirm is this is the case is to put a force gauge on a roller band when it is loaded and see if it is close to the force of both bands on a conventional gun.

From the calculations I did earlier, the best case scenario would only result in about a 20-30% improvement. for a lot of people this isn't worth the extra complications associated with a roller.

Quote from seal

The idea of the puleys is to break the speed limit of normal bands.Every shaft has a limit that can be accselerated to with normal bands.Even if you store five time more energy in multi bands configuration,you will give to the shaft only a small part of it,the rest will go for recoil and drag.
The idea of the pulleys and rollers generally is to aply a reasonable pack of energy to the shaft and get high velosity with minimum losses.
I cant understand how people still wonder and dont understand that.Its so simple and we prooved it thousand times.'Its completely same relation between compound bows and classic bows.I came home from the US with a compound bow and can say that it is ten times better than the recurve.

seal-- I love the craftsmanship of your guns and I respect your opinion on the concept of roller guns, however
this ^^^ is just another vague analogy/opinion without proof, like formulas and math that PROVES nothing.
I was directly involved with the Research and Development and field testing of the compound bow by Holles Allen and Jennings Co. back in 1969, so I KNOW and understand the concept/advantages/disadvantages of wheels. IMO, just measure true spear speed, like we did in 1969 with a clock and you have your winner and your loser. Simple/done.

To compare "apples with apples" I used the same travel length for the barrels and the same band stretch in terms of the force to pull the band onto the wishbone notches or shaft tabs using the same type of rubber. The double band conventional gun receives twice the initial force (F max x 2), but the bands are shorter and only push for part of the barrel length while the rollergun pushes all the way with one band using only F max at the start. However the rollergun equipped with two bands (twin axles or doubled pulleys) does store more energy than the two band conventional gun as if you do the same manipulation on the energy diagram you get a longer rectangle extended by the length of the extra powered travel distance. Of course the energy diagram is not a rectangle as it should be two triangles stacked on top of each other giving a much taller triangle, but what we are interested in is the area for comparison purposes and it is easier to see as a rectangle. Basically a rollergun uses longer bands on a gun than it would normally be able to accommodate and you can do more with them in terms of the stretch and their routing on the gun because there is more linear space available to locate them. The term "rollergun" embraces a number of configurations that are different guns in terms of the energy that they can store, hence comparisons can be complicated when trying to work out what their equivalent is as a conventional gun. Some time ago I did a bunch of rollergun diagrams here to explore this variation as there certainly is no magic ingredient involved and rollerguns usually shoot a shorter shaft for the bands that they use as the rollergun is basically a longer gun folded up on itself.

A conventional band gun is more of an impulse weapon than a rollergun is as the shaft acceleration is short compared to the more progressive push the spear receives from a rollergun (as the energy triangle is stretched out and the "toe" of the triangle is often not used). The rollergun will be a wider gun if it uses enclosed bands as the pulleys push out the width of the stock and that will change other characteristics of the gun that help determine its shooting performance in terms of muzzle lift. Although rollerguns seem new they were around decades ago, but modern materials have made more complicated guns much lighter and stronger than they were in the distant past, particularly with the cable rollergun where bands don't have to travel around rollers at the muzzle as in a sense elongated wishbones do that job and they are no longer steel cables.

Quote from hau

seal-- I love the craftsmanship of your guns and I respect your opinion on the concept of roller guns, however
this ^^^ is just another vague analogy/opinion without proof, like formulas and math that PROVES nothing.
I was directly involved with the Research and Development and field testing of the compound bow by Holles Allen and Jennings Co. back in 1969, so I KNOW and understand the concept/advantages/disadvantages of wheels. IMO, just measure true spear speed, like we did in 1969 with a clock and you have your winner and your loser. Simple/done.

Sure Im working on gettin a chronograph.
BUT the easyest and simplest way to compare the speed is the PENETRATION.Anybody could do this.Speed=energy=penetration.This is what we need and its done many times.The penetration of normal guns always looks poorer compared with even smaller rollers.The complicity of rollers comes from bad builds or is a myth invented by the haters.I proper made roller is easy and relieble as any other gun.
I dont have any fake reason to defend the roller idea.I am making classic guns with the same success.But if a friend asks me for advise,I will make him a roller;);););)

Quote from seal

Sure Im working on gettin a chronograph.
BUT the easyest and simplest way to compare the speed is the PENETRATION.Anybody could do this.Speed=energy=penetration.This is what we need and its done many times.The penetration of normal guns always looks poorer compared with even smaller rollers.The complicity of rollers comes from bad builds or is a myth invented by the haters.I proper made roller is easy and relieble as any other gun.
I dont have any fake reason to defend the roller idea.I am making classic guns with the same success.But if a friend asks me for advise,I will make him a roller;);););)

1. "Speed=energy(weight) =penetration".----true
2. "This is what we need and its done many times.The penetration of normal guns always looks poorer compared with even smaller rollers".-----opinion (unproven)
3. "The complicity of rollers comes from bad builds or is a myth invented by the haters".-----opinion (unproven)
4. "I proper made roller is easy and relieble as any other gun".----false (if proper made roller guns are easy, why do they:
a. cost more? ----(proven)
b. is wheels/axels/bottom attachment points/dedicated muzzles "easy and relieble" as a conventional gun?----false
5. "I dont have any fake reason to defend the roller idea.I am making classic guns with the same success.But if a friend asks me for advise,I will make him a roller"----opinion

Please to keep in mind that what we are discussing here is a comparison of a simple roller gun to conventional gun. A roller gun with enough extra rubber and multiple pulley combinations and attachments and cable CAN shoot a same weight spear at same speed as a 2 band conventional gun--opinion

It is tempting to think compound bows have higher performance due to the pulleys or rollers which are usually cams, although on a crossbow they will be pulleys as on a crossbow there is no need to reduce the pull of the bow at full draw so you can hold the arrow while waiting to shoot as the trigger mechanism does that job. The cams create this effect by changing leverage as they rotate which changes the pull experienced on the bowstring of the bow to provide a let off where the force required to hold the arrow reduces significantly from that required to draw the arrow back. Unlike a recurve bow the pull transfers from the opposite bow limb which can be much shorter and stiffer as the pulleys have a Buss Cable that connects to the opposite side of the bow. Besides the advantage of higher energy storage available in deflecting stiff bow limbs the limbs can be disposed in a more horizontal configuration so that bow recoil is reduced by the limb movement cancelling out top and bottom. Recoil in a bow is forwards, not back as the vertical limbs flip forwards in a conventional bow.

Where there is a similarity with rollerguns is that the "energy storage battery" can be separated from the transmission element whereas in a conventional speargun they are one and the same thing. You have a lot more freedom to vary the "band battery" and that is what seal does with his guns using cables and rollers.

Claiming the comparison of a "simple roller" to a conventional speargun is like comparing a longbow to a compound. There's nothing simple about it...

I own and shoot compound bows regularly. Two different systems.

Drumroll please................

(Video is uploading to Vimeo)

Gun on left: 57" custom double action roller with 57"-5/16" shaft

Gun on right: 57" Wong MGS with 2- 5/8" bands and 57"-5/16" shaft

C

They do appear to go off simultaneously. How'd u pull that off?

Looks about the same.

Any chance you have a fishing scale that will go up to 100lbs? If so can you measure the force of each band on each gun?

I see a faster shaft from the roller gun and definitely less recoil. Seems very clear to me.
Chuck thank you very much for this.

Quote from Dan

For anyone getting confused again about what we're comparing, Chuckd has it exactly right, apples to apples as long as the bands are the same diamter.

And I'd suggest same length bands, and stretched to same percentage. Thoughts?