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All About Guns What's your weapon of choice, and why? Discuss the beloved speargun here!

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Old 05-05-2020, 01:26 PM   #61
musubi
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Re: My Invert Roller

Update to my two invert guns. In using the Harken pulleys (or any pulley actually), I was getting an issue on the bottom band sets where one set of bands was pulling on the 2nd pair through the pulley. Let me explain:
The below picture is how things are at rest.


The picture below shows a representation of how things look when I'm pulling one pair of bands. You can see it pulls on the second pair through the pulley.


The picture below shows my solution. I wrapped the two dyneema parts in BCY Halo serving that I had from my archery equipment. It's actually spectra, but small diameter. I did this on my bluewater gun and tried it out this past weekend.


So all of this was meant to address more of an annoyance than a concerning problem. Every time I'd load the bottom bands, the bunching would happen at the pulleys and I'd have to even out the sides because one side would be longer than the other. This created additional friction in the area under tension and was slowly causing some wear to the dyneema.

I did this to my bluewater gun and tried things out this past weekend. Things went better than expected. Not only did the wrapping hold up, but I found it much easier and faster to load the gun because the loose bands on the bottom weren't getting as tangled with everything else. Because they were tied, it prevented those areas from crossing over places and getting tangled.

One other thing I did to my invert guns is place a 1/8" SS rod through the Harken pulley axle. The axle is actually a tube and the 1/8" rod actually fits perfectly in there. I epoxied it there and you can somewhat see it in my pictures above. Honestly, the pulleys are probably fine without it, but I like having things beefed up a bit.

The following is a very short clip from this past weekend just showing the gun shooting, since I've never posted a video before.
https://i.imgur.com/HODY4Mj.mp4

Hopefully you can see it. It was a Kamanu (Rainbow Runner) amongst a school of Kawalea, or Heller's Barracuda.





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Old 05-05-2020, 05:01 PM   #62
popgun pete
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Re: My Invert Roller

A nice looking fish and pretty good to eat. Interestingly you were tracking another and he swam into the shot, that is karma.
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Old 07-29-2020, 09:17 PM   #63
musubi
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Re: My Invert Roller

Another update to my thread. I built another invert:
It's a 110 cm gun.

- Carbon cuttle barrel, matte finish
- MVD handle, muzzle, and reel
- RA 7.5 mm shaft

I built it to use as my main gun and have my current gun as the backup.
I ran the shooting line on the side of the gun, as I've done with my other inverts, to keep the line away from the bands and pulleys. I think I just wanted an excuse to build something again.

I'm running 1 x 16 mm band for my initial pull and 2 x 14 mm bands for my other pulls. Trying that combo out to see how it works.

I was really set on using foam to fill the inside of the barrel, but shipping to Hawaii is outrageous and the product shelf life is 6 months. It just wasn't worth it. So I didn't fill with anything, but I did do my best to pre-ballast things and I really didn't need to fill with anything (like clothes, haha). I did add some shot pellets to the handle and muzzle. I"ll be taking this gun in the water this weekend to see how things go.







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Old 06-04-2021, 02:08 PM   #64
Galen
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Re: My Invert Roller

Beautiful guns! Where do you find those narrow black delrin wheels/pulleys for the cable rollers?

I have been researching roller guns and invert set-ups for a while. Thanks for sharing, and thanks for the test results comparing different diameter shafts.
I have some thoughts concerning the tradeoffs of muzzle velocity, power, and shaft weight:
1. Friction drag on the spear increases exponentially with velocity--a light shaft will leave the muzzle with more velocity, but slow down faster.
2. increasing shaft diameter will reduce friction drag through the water due to a slower-moving, heavier spear.
3. My goal is to maximize accuracy + distance that penetrating power is maintained.
4. heavier spears can handle more power with less shaft whip, causing some improvement to accuracy with more powerful band setups
5. Penetrating power is largely based on momentum
6. So my big question is, how do we flatten the force curve produced by the bands, similar to a compound bow using cams and pulleys?
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Old 06-04-2021, 05:47 PM   #65
popgun pete
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Re: My Invert Roller

Compound bows just reduce the pull at maximum draw so that the archer can easily hold the arrow against the pull of the bow. The cams/pulleys are torque devices that vary the effort depending on how far away the pull is being taken from the pivot of the cam on the end of the bow limb. The greater the radius then the force required to hold against the bow pull becomes much less. Same idea as using long spanners to undo tight nuts or bolts, the effort required becomes much lower to apply a high torque the further out you hold the spanner. As spearguns have a trigger mechanism to hold the shaft they don't need a low pull at maximum band draw.

What often goes unnoticed is the pulley in a compound bow pulls on the opposite bow limb through the two buss cables that run vertically in the bow.

The only speargun that uses cams is the “Dreamair”, the cams being spiral track winding drums both in and outside the body of the gun which is basically a pneumatic winching system, albeit a high speed one.

Last edited by popgun pete; 06-04-2021 at 05:58 PM.
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Old 06-04-2021, 07:06 PM   #66
musubi
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Re: My Invert Roller

Quote:
Originally Posted by Galen View Post
Beautiful guns! Where do you find those narrow black delrin wheels/pulleys for the cable rollers?

I have been researching roller guns and invert set-ups for a while. Thanks for sharing, and thanks for the test results comparing different diameter shafts.
I have some thoughts concerning the tradeoffs of muzzle velocity, power, and shaft weight:
1. Friction drag on the spear increases exponentially with velocity--a light shaft will leave the muzzle with more velocity, but slow down faster.
2. increasing shaft diameter will reduce friction drag through the water due to a slower-moving, heavier spear.
3. My goal is to maximize accuracy + distance that penetrating power is maintained.
4. heavier spears can handle more power with less shaft whip, causing some improvement to accuracy with more powerful band setups
5. Penetrating power is largely based on momentum
6. So my big question is, how do we flatten the force curve produced by the bands, similar to a compound bow using cams and pulleys?
Thanks! The wheels in my gun were part of a kit from MVD, so the muzzle head was pre-assembled.
But if you're trying to source individual rollers, two main places come to mind. One is Aoshun Spearfishing Supply. I believe Dean can make whatever size you desire. Also Ermes Sub has some sizes you can work with.

MVD has a couple sizes of invert rollers you can purchase by itself.

If I'm understanding you correctly in flattening the force curve, you'll want to find something that maintains a steadier force through the band pull, maximizing the power stroke. Meaning, you'll want longer bands (as to not dissipate quicker as with shorter bands) and sufficient pre-stretch. I think the only style gun that comes closer to that are those inverts that run the first band pair from the top to the bottom (using those rear pulleys).

What kind of fish are you shooting and how far would you like to be effective at?

Right now, I've only been working off of exit velocities for my setups. How much power is maintained further down the shot is based on field testing only. And for me field testing is shooting fish. I could definitely make my invert setups much more powerful and if that were my goal (not saying it's yours), I would be limited by the shafts ability to maintain a straight path (not flexing or exceeding the terminal velocity, recoil (if there is much to be had), and the gear holding it all together.

I can only tell you at this time what has been working for me, primarily in the reef setting. The 7.5 mm RA shaft has been shooting consistently straight with 340% stretch with my 14mm and 16mm bands setup (Primeline). They run 1" pre-stretch. The gun is very powerful and accurate. I've been able to capture fish at the end of my double wrap if I'm pushing it. Normally if I'm shooting that far it's at our invasive grouper species, Roi (for target practice). 90% of my shots otherwise are very close as I just need that assurance for an ethical shot.

If you're trying to achieve what the cams do in a compound bow with significant letoff (70% to 90% let off), then I can't see it being needed, like Pete mentioned.
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