There should be a new forum rule where you can't post food pics without the recipe. Haha.
Posts by Wishihadgills
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They still capture and sell tropicals in the Keys as well.
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Picture was fine, got point across, I know who you are now, didn't catch it earlier. :crazy:
Dan's part would work, doesn't fully retract. A round housing to fit a Flashlight mount might be going to far.
Don't see an easy way to add a spring to Dan's part so it's locks in either position.
Where is George, he's the idea guy.
I don't see an easy way to retrofit a spring to Dan's part but I do have a couple ideas for a new design. I'll try to sketch something tonight to explain.
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I guess I'm just a sucker for the production quality. Something about the camera work does it for me. To each his own.
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Awesome video. There are some really cool and very friendly fish but I think I have to disagree with you on the best video ever. My favorite is this one from Perrin James.
[VIMEO]65749730[/VIMEO]
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Does anybody here subscribe to Ultimate Spearfishing Magazine? I just saw an advertisement about an article comparing/testing roller guns. I don't have any more details than that. Might be worth checking out .
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No argument on the elongation here:D.
Hank: When you start getting into penetration you open up a whole new can of worms.
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Hey Xan, I don't think that you can use the Work = Force x Distance calc in any case, as the force is a function of band elongation. The energy would be the area under the graph of force vs elongation,
so you would use Grossetti's function of 1/2kx^2
But Grossetti's calculation is flawed because stiffness is inversely proportional to length.
As k=EA/L, and the theoretical roller gun in Dan's example has a rubber length of twice the normal gun, its stiffness is half of the single band. As there are two parallel rubbers for the double band gun, its stiffness is twice a single band.
Stiffness
Single band k = 1
Double band k = 2
Roller band k = 0.5
Elongation
Single band x = 1
Double band x = 1
Roller band x = 2 (as it is half as stiff, you can stretch it twice as far for the same loading force)
Energy
So applying E=1/2kx^2
Single band E = 0.5
Double band E = 1
Roller band E = 1So Dan was right all along.
I know that force is a function of distance. The forces I used are the max forces applied. Yes you are correct in saying that the work would be the area under the curve. Notice however that the bands are linear and the conventional band although starting slightly higher quickly drops to 0 while the roller band gradually decreases to a value slightly above 0. I did not show all this this because I had no way to to measure the exact outputs of the bands at different elongations. But because they are linear you could use average force applied over the distance. I have not done the calculations but I don't think this will change much. Maybe the final values but not the overall results.
In Grossetti's calculations yes the stiffness are different. The K value of the conventional bands is exactly double. However it is also being stretched nearly 2 times as far.
You are forgetting that a roller gun has 2 bands just like a double band conventional gun. So yes if you compared a roller with only one of its 2 normal bands then yes a double banded conventional gun would be more powerful. That is why as Grossetti pointed out if you added a a 3rd band to a conventional gun it would have more power.
K
Conventional gun K = 2
Roller gun K = 1Elongation
Conventional Gun x = 1
Roller gun x = 2 (its actually closer to 1.6)Potential Energy (1/2*k*(x^2))
Conventional gun = 1
Roller gun = 2 (or if you use 1.6 for x ) = 1.28It is the X^2 (x squared) term in the Potential Energy equation that makes the distance SO important. It is also key to point out that in the energy equations this X is total distance not elongation relative to the length of the band. Also notice 115cm /1.28 = 89.8 cm. Which is very close to the 87 cm my initial calculations for the length of a roller gun with the same energy as a 115 cm conventional gun.
P.S. Thanks Dan. I am both excited and nervous moving on to the next part of my life.
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When you reduced the 115 band stretch by 38.5 you conceded that there are 4 bands instead of two. Think about it.
Whether you call it 2 bands or 4 bands it doesn't matter. Either can be modeled as 1 spring that applies a force to the shaft. The roller gun would also have 4 segments. The 2 segments on top that pull on the shaft and the 2 segments on the bottom that pull on the top two segments. Forces are additive so the force of the bottom 2 segments adds to that of the top 2 segments and you get the same result. As you said the bands are the same and I treated both sets the same. In my calculations both guns have two 77 cm bands.
I started with a force value of 80lbs which is a fairly reasonable estimate of an actual band. This number can be higher or lower based on the exact band used. Then using your statement that the bands on a roller and a conventional gun where exactly the same, along with the assumption that the bands where perfectly linear, I calculated the force output of a roller band based on elongation relative to the conventional band.
P.S. Sorry if my calculations are confusing/boring. I tried to explain as I went along and show most of9 my math. Also in case anyone was curious as to my background in this, I study mechanical engineering at Georgia Tech. I graduate in two months (kinda excited).
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The force is not generated per segment. It is a total force applied to the wishbone. If two bands applied 360 lbs of force then each would be 180 lbs and 90% of people could not load them. Either way the bands are the same. When you stretch the same rubber by the same amount you get the same force.
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If you choose to look at it that way then it should multiplied by 4 not by 2.
The 2 in that equation has nothing to do with the number of bands/segments it comes from the equation for kinetic energy 1/2(m)(v^2). In my calculations the bands are being modeled as simple springs.
Hau careful when you get to 400% elongation or more. Depending on the rubber you have this is pretty close to the elastic limit. Beyond that it becomes harder to pull the rubber but it will start to cause permanent deformation to the band. This has two problems, one is a dramatic decrease in band life and two because the band does not completely return to normal it ends up being slightly weaker than the amount of force needed to stretch it that far.
As for pre-tensioning, it will improve the power but as Dan mentioned it usually makes it more difficult to load than it's worth. Some guns like the Beuchat have the long main band and then multiple smaller bands on the bottom. This makes loading easier (and slower) but allows for you to increase the overall force slightly.
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38.5 is 77/2. This is the position on the track at which the conventional band is in its relaxed state. In its relaxed state it no longer applies any force to the shaft.
I've read an article about testing rollers and non rollers and, according to the tests, to get the most out of rollers, the band should be pre tensioned...
In the calculations I provided the band is pre-tensioned. Not much but slightly; the band is roughly at 110% elongation when it reaches the end of the gun. The pre tension is determined by where, on the underside of the gun, the band is anchored.
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I went at it a bit diferently from Wishihadgills, but I end up with the same type of results:
You did the extra work of looking up real values of the bands which I applaud. I was working off the assumption the bands would be the same and was just doing a rough analysis to prove a point.
I recently had an interesting realization. If band thickness is the same and elongation is the same the force should be equal. Most guns use the 300% elongation rule and therefore longer guns have longer bands. So why would a longer gun have more range/power? Excluding a slight increase in the mass of the shaft the answer is that they apply very similar forces over a longer distance. The only thing a roller gun has done is to change the location of where the relaxed band is located.
Imagine for a second you had a 100 cm long gun. When the band is relaxed the wishbone is roughly 75 cm form the muzzle. Put an imaginary hinge right where the wishbone is and bend the tip under the gun. Put a roller at the new tip for the band to go around and now you have the idea of a roller. Same bands same everything but now the gun is only 75 cm from mech to tip. Not magic just a clever use of physics.
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The elongation was calculated using the assumption of the same size band (which was one of Dan's original points of contention). The the roller band is stretched differently because it is oriented length wise. Relative to the full length of 77cm the band is not stretched 3 times its length, which would require 231 cm of stretch instead of the 200 it actually sees.
5 cm is the circumference around the roller. Ciricumference = 2*pi*radius = pi*Diameter. The band travels around half of the circumference so the full circumference would be 10cm. 10/pi = a diameter of about 3.18cm or 1.25 inches. Maybe a bit large but certainly not unreasonable and 5cm was a nice round number. You could make that value slightly smaller and it won't affect much even if it was zero. 195 cm vs 200 cm is only a 2.5% difference.
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Ok. I had a little free time to do some rough calculations. Maybe this will be enough to convince you it is in fact "possible."
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Makoa how's the range of your 110 roller compared to when it was 140 standard? I've read that one of the benefits of the shorter roller is not only power, but supposedly the range as well.
Range and power are the same thing in this application. You can't have more of one without more of the other.
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3mm 77 degrees and up. I have under 10% body fat so I think that's a factor to my ability to adapt to cold. Above 82 degree I use my rash guard suit combo with the vest.
I'm with you. I get cold and most of those numbers do not reflect my personal ranges and in hind site could all be bumped up a couple degrees for a more realistic view but I was just putting minimums.
I wear my 3mm all year in Miami. In the very warmest parts of the summer I will put on 1.5 lined pants to allow water circulation. In the winter I might look into a 5mm top or maybe a full suit.
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Dan I think grossetti and I have both described how a roller gun has potential to be more powerful in a shorter package. Whether they are or not is going to be a function of the band combination used. This is true of any band gun. I can make a my riffe more powerful than yours if I put heavier(more) bands on it. If we take that to the limit, and put the heaviest bands that can be loaded by the user the roller gun will have more power because it can apply the force for longer. That is physics plain and simple. But I also agree that they are not always (maybe not even usually) the best option but they do have their advantages.
Like someone mentioned their advantages are similar to this of pneumatics which are also more powerful than an equivalent length band gun. Pneumatics also have their own problems but thats another discussion.
Chase I think you are misunderstanding the term "shoot slower." Because they accelerate the shaft with a smaller force for a longer distance it takes longer from the time the trigger is pulled until the shaft is no longer in contact with the bands. It feels slow but this does not reflect on the final velocity of the shaft when it leaves the gun. The addition of the single band speeds up this process but still allows the roller band to apply force over the last tip of the gun.
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Chase: I wasn't analyzing a particular brand of roller gun. I was simply explaining from a physics point of view why a roller gun "can" produce more power than a conventional gun of the same length.
When it comes down to it there is only one way to produce higher velocity more force for longer time. If it does not move the shaft faster then it won't have more power and nobody would be claiming that. There is no magic.
There are two tests that can be done pretty easily. One is check the velocities with a chronograph to see if they move the shaft faster. The next is hook a force gauge on the bands at full stretch to figure out how much force they produce. A fishing scale will be accurate enough for this to work.
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Very personal thing but I'll take a stab at it.
Rashguard: 74 F and up. I've seen people where it when its colder but not for long and they were not comfortable
1.5 basically the same as a rashguard but maybe useful for a few more degrees. Maybe 70-72 F Plus
3mm: 66-68 F. Maybe lower but I get cold diving all day. It also hasn't gotten much colder than that down here.
I don't Have any experience beyond that.
