Progressive band setup?

[JCooke]

this is trueing into the ago old debate "size matters"I think ill just start puting some drawing to paper and build and test the thing.Posted via Mobile Device

 

[Tin Man]

This should either help, or muddy the water completely. Draw a chart like the ones below, with band pull force on the vertical axis, and band pull distance on the horizontal. The line for a particular band setup connects two points. At the top right, is the point of max band pull distance (from the muzzle) and max force. At the bottom left, is the distance (from the muzzle) where the band goes slack. The area under the line you drew, is the maximum potential energy that the band contains, neglecting friction and such.

On the left, is a typical 5/8" band. If the band is 20" total length, then it is slack 10" from the muzzle. Stretched to 350% of its original length, gets me to a point 35" from the muzzle, and around 120 lbs of pull force.

The chart to the right shows why a roller gun gets more bang from the same size package. The bands continue to pull all the way to the muzzle, and may even be preloaded at that point. So they never go slack.

So, if you plot the different attachement points for the bands that you are considering, you can compare the area under each line to see how much energy is available.

Edit - Also consider that old formula Force = Mass x Accelleration. If you try to accellerate a shaft to final speed quickly, you get more recoil than you do by applying lesser force over a longer length.

 

[JCooke]

well heres another nugget to chew on.....a progressive roller.jasPosted via Mobile Device

 

[hteas]

Jason,
There's one thing missing so far.
The bands provide maximum power only when at maximum stretch. A decreasing amount of power is provided as the shaft moves forward. By the time the bands are at normal length they are providing no power. No matter what combination of bands you use, the shaft will still be in the gun when this happens.
with that said, the 3 length bands will provide all their power over a shorter time period. Since you want overall performance, not just peak power (which will be the same for either band configuration), you are better off using longer bands to apply the power over a slightly longer spear travel length. The longer bands, pulled to the back of the gun will continue to provide power to the shaft, fightling inertia for slightly longer, and getting the spear further before inertia slows it down.
The other problem is that notches weaken a shaft. More notches weaken it much more. Notches well forward on the shaft are just begging for a strong fighting fish to break them.
My 0.02$
Howard

 

[JCooke]

i was thinking fins and when i get time ill have myson work out a formula, hes a college math nerd. it should be pretty simple to get on paper.so your saying sacrifice overall power with performance.I work on it tonight a see what my brain comes up with.Posted via Mobile Device

 

[JCooke]

so to recap....a 63" gun fully enclosed track, three bands of different sizes, two of them being way over powering for a 1/4 inch shaft out of the track, located down the barrel in three different placesso that one monster pushes only till the shaft tip give or take just leaves the track(and for max power make them all roller to use as much push as poss) one semi monster pushes till its 1/3 out of track and the last pushes all the way through. shaft 38" with 3 shark fins.......Posted via Mobile Device

 

[Tin Man]

I've never seen a three banded roller gun. The muzzle is gonna get pretty big. And it will still be less power than three identical full length bands.

I think that a 3/4" band is around 150-160 lbs at 350% elongation. If you stretch it much more than 350%, bad things happen. It will relax over time, and won't snap back as fast. And the life of the band will be much shorter. If you look at the sample graph that I posted, you'll see that a shorter band at 150 lbs will not store as much energy as a band twice as long at 120 lbs. Your idea, I think, is based on the assumption that you can use a shorter band of extreme force. But even if you could cock it, there are limits to what a 3/4" latex band can do.

 

[JCooke]

k,this is interesting...Now I havent heard any body or thing about the fact that the bands are only pushing the weight of a 1/4 shaft say 38". that has to have a big effect in this discution.JasPosted via Mobile Device

 

[Tin Man]

I think you have two separate issues. One is the use of "progressive band" attachments, such that the three bands are not all anchored at the same point. Shooting a shorter or smaller diameter shaft would be a related, but different, discussion, yes?

 

[JCooke]

and the water in the trackPosted via Mobile Device

 

[jtkwest]

I think you have two separate issues. One is the use of "progressive band" attachments, such that the three bands are not all anchored at the same point. Shooting a shorter or smaller diameter shaft would be a related, but different, discussion, yes?

word aka:my sentiments exactly.

 

[JCooke]

Dam not one positive thing about the idea.I give.Posted via Mobile Device

 

[DivingDane]

it is an interesting concept but the other s are right, 3 bands all stretching over the longest possible distance will store and release more energy than staggered bands as a small amount of material can only store a relatively low amount of energy, compared to a larger amount of material.

as far as not being at the cutting edge of design with single rubber guns and thin shafts, i'd argue that American guns are archaic by comparison to the technolgy and design being used in european guns. so the reverse is probably more accurate. nothing against the US but using a huge slab of would with 3 bands and an 8mm shaft to shoot large jacks or seabass is overkill,

a correctly designed gun with a lore stramlined shape and slighlty finer shaft is more than adaquate enough, for medium to large game fish hunting i believe that someware between the Southafricans and the Europeans is the way to go.

small enough and fast enough to amneuver for smaller preay yet accurate and powerful enough to land large game fish.


- Rob Allen
- Orca etc
- C4
- Bluetec
-Trygons

particularly the last 3 are light years ahead in design to say, Riffe. a good gun in its own right.

just my opinion which doesnt mean much but i know that when hooting a variety fo fish on a deep reef trip where anything from, Sea Bream at 2-4kg through to Jobfish up to 10Kg and then through to Wahoo and Dogtooth tuna to well over 60kg can be expected an allrounder like those mentioned above was far and away not only the most popular but also the best choice for the trip.

DD

 

[JCooke]

I get what everyone is saying...I was seeing if I could supercharge a small spear while supported to have the same reach or farther, and punch through a fish at high velocity. Rather than 3 rated equal length bands for that shaft.

Like a .17HMR vs .17REM rounds.

thanks guys
Jas

 

[DivingDane]

i understand what you were trying to do, and ideas like this is what helps the sport to evolve.

understand the rifle idea yiou have given but the problem is that what you are propsing is more like using a .17 hmr but with reduced powder load. because the energy cting on the projectile is less i guess its similar to shooting a bullet out of a short barrel v a long barrel, the gasses propelling the projectile are only effective over a short distance.

like i said nothing wrong with having the idea, its great to be able to ask people as experienced as many are on this forum we have alllll learnec much from each other.

an exclosed track gun will negate almost allthe issues you were trying to fix in the first place, see companies such as trygons with multirubber setups on 6.3mm shafts in enclosed track guns.

DD

 

[behslayer]

Wow, this thread seems to be bouncing all over the place. Band Placement, Shaft Diameter, etc. My understanding is that the original goal was to get a Shaft to move faster, with more power.

I understand the concept of trying to have forceful pull on the shaft for the entire length of the Barrel. But I think there comes a point where you are chasing your tail here.. Rollerguns try to address this issue, pneumatic guns do address this issue, but with standard Rubber powered guns there is going to be a 'dead' zone when the band has returned to it's resting state and though it may continue to push as it recoils, it is no longer pulling.

If the goal is to get the shaft moving faster and with more power there might be better/easier ways to achieve this.

There's some discussion on Shaft diameter. I'm going to throw in another element which is shaft composition. Sure, a thinner shaft of the same material will move faster, but with less velocity as it is lighter, and is more prone to bending. I've been using some of the Rob Allen South African shafts in thin diameter. I'm not sure what the exact material or process is, but those shafts seem heavier than 17-4 shafts of the same diameter and length, and a hell of a lot harder. I've never bent one, and couldn't imagine snapping one. More weight, thinner diameter, less prone to shaft whip = more speed and velocity and accuracy.

Enclosed Track.. increase your band power.. prevent shaft whip by using an enclosed track and be able to use a thinner shaft.

Track composition. I know this has been debated.. Whether the composition of an track really affects the end speed of a shaft travelling through it. Some will say that whether using a Wood track, or a Composite track, that during the firing process, a film of water surrounds the shaft anyways.. For my personal guns I have occasionally put some lengths of small diamter stainless rod along the lower sides of the track spaced the length of the barrel. Yes, it makes a Zing when it shoots.. and I have no test data to prove that the shaft shoots faster out of the barrel or longer, etc.. but it sure seems that way. The fact that there is a Zing when shooting underwater, makes me think that there is some compression of the shaft onto the track surface. Above water, if I place the gun on even a hardly noticeable incline and release the shaft without any bands, the metal on metal slides effortlessly.

 

[gserghiou]

A. band holes or band attachment to the complete font part of the gun....

B. inverse trigger mechanisms...

C. shark fins to be placed waaayyyy back on the shaft (as much as possible).....

forget about roller guns and lets concentrate on 'normal' guns....

lets keep in mind that many variables are constant ie, band diameter, elongation ratio, rubber quality......

all the above (point A,B,C ) are 'upgrades' for one and only reason .... to achieve MAXIMUM BAND ELONGATION DISTANCE , that is the distance for which the rubbers will be pulling the spear, before they disengage..... (ie the distance from the band holes, to the end shark fin - the rubber length )

placing 3 bands (progressively as mentioned) is like reinventing the wheel, but this time making it square :rcard..... WHY sacrifice all the pulling distance (which gives us 'power') that you could get from the 1st and second rubber.....????

further to this, i think shoting a gun with the progressive setup as described, would give the shooters hand 2 'extra' little kicks when the 1st and 2nd rubber 'detonate' ??? maybe im a bit high now:friday .....

George

 

[JCooke]

Wow, I throw a candy bar in the pool and eveyone thinks its a turd.

K, Lets get to the core of this discussion, my allergies have givin me a moment to think just a little. Alright my first point plain and simple, adding more pulling power to a small shaft placed in a big gun.

Speargun Band Power : Spearitco.com, The worlds largest selection of Speargun Bands and Do-It-Yourself Spearfishing Supplies

Now according to this(chart at bottom), say for arguement, that this same shaft in a small size apropriate gun would use probly two 1/2" bands equaling 280lbs of peak force at 300% stretch. Not knowng the weight of the shaft I cant figure how fast that shaft would travel with that much force,plus drag,friction,and million other variables.

To keep it simple, with the bands I want to try 1 each(9/16,5/8,3/4)= 728lbs of peak force at 300%stretch natural rubber. All 728 lbs pushing in the track and decreasing throughout the shot. Where the shaft would be at speed before leaving the track, and the last band pushing almost the entire distance. I dont know the retraction speed of rubber either.

For the time being Im keeping the micro technical stuff out of it cause its endless.

A ruff ruff drawing is attached and I know the dimensions will need some tweeking but its in a nutshell what plopped into my head.

To follow the rest of the negectivities here of the idea, the water in the track before the shaft will need somewhere to go also.

Another point does shaft whipping,flexing or bending come from pushing or from reacting with a always moving water, cavitating, drag?????? or all.

Is there a terminal velocity of shafts in the water

Jas

Just as a challenge to everyone any ideas to make this possible and fuctional and produce the results wanted.

 

[Tin Man]

If you are saying that the band setup in your sketch will produce more energy than two 1/2" bands, then possibly it would (I would have to chart it). But I still don't understand how your plan is superior to anchoring all three bands in the forward hole?

It is not uncommon for people to mix band sizes, for example one 5/8" band and one 3/4" band. Typically they load both for longer shots, and unload the larger band if they are shooting into a hole or something and need considerably less power.

Shaft whipping, like an arrow flexing, is based on the same phenomenon as buckling a long skinny column. If you squeeze the ends of a thin stick or reed between your thumb and forefinger, it will want to bend and buckle in the middle. In the case of a shaft, we have a forward force at the trigger end applied by the bands. The rearward force from the other end comes from inertia based on the mass of the shaft, combined with any other forces that resist the initial forward motion (like friction, water in the track, etc.).

 

[behslayer]

"But I still don't understand how your plan is superior to anchoring all three bands in the forward hole?"

What he said.