Inverted Speargun accuracy problem

[Andrew the fish]

Wow.

If you move your gun fast enough (tracking the fish), shaft will be continually pulled to the side by water drag. Shaft has plenty of time while it is being slowly accelerated, longer portion of the shaft will be hanging outside the gun, unsupported, lateral flow of water will continually drag the shaft to the opposite side of lateral movement of the gun. Nothing about rubber uneven stretch or anything else. You can't fix that, unless you have something like enclosed track maybe?

Basically, imagine that water holds the shaft, which is already half way out of the barrel, and you are ripping it to the side with the later movement of the gun. Like friend of mine said ( he is looking over my shoulder now) "basic fluid dynamics".

There is more to it. Once the shaft is ripped out of the track, like seen on your picture, the shaft becomes inherently unstable because it is being accelerated by its rear end. It is like a rear wheel drive sports car. The bigger the misalignment between the shaft axis and direction of the accelerating force, the more it will try to fly off to the side.

 

[popgun pete]

Wow.

If you move your gun fast enough (tracking the fish), shaft will be continually pulled to the side by water drag. Shaft has plenty of time while it is being slowly accelerated, longer portion of the shaft will be hanging outside the gun, unsupported, lateral flow of water will continually drag the shaft to the opposite side of lateral movement of the gun. Nothing about rubber uneven stretch or anything else. You can't fix that, unless you have something like enclosed track maybe?

Basically, imagine that water holds the shaft, which is already half way out of the barrel, and you are ripping it to the side with the later movement of the gun. Like friend of mine said ( he is looking over my shoulder now) "basic fluid dynamics".

There is more to it. Once the shaft is ripped out of the track, like seen on your picture, the shaft becomes inherently unstable because it is being accelerated by its rear end. It is like a rear wheel drive sports car. The bigger the misalignment between the shaft axis and direction of the accelerating force, the more it will try to fly off to the side.

Don't get too excited, the image distortion is a product of the shutter, read the previous post. The shaft hit the fish.

 

[Andrew the fish]

Don't get too excited, the image distortion is a product of the shutter, read the previous post. The shaft hit the fish.

I get it about distortion caused by shutter. But first image on the initial post clearly shows the shaft being off the track and to one side. This is not an image artefact.

 

[popgun pete]

I get it about distortion caused by shutter. But first image on the initial post clearly shows the shaft being off the track and to one side. This is not an image artefact.

And that is probably due to uneven band pull side to side as stated earlier.

 

[Back2Narnia]

Maybe a combination of all these factors. Nevertheless i ordered a bunch of new rubbers and an enclosed track...maybe i will glue it on temporary and see if it makes a difference.
Also i bought new bearings that i may upgrade with different rollers if i find some that will fit.

How much rubber do you think i need to push a 7.5mm Shaft at perfect velocity? Ordered 1.5 meters of 14.5mm and 17.5mm small ID bands.
Also off topic but my 8.5mm shaft collects dust crazy fast...any solution to keep it from rusting other that oiling it up?

 

[popgun pete]

As for the rubber you will need to experiment as every batch can be slightly different, you can shorten bands, but not make them longer without replacing them. Squirt your shaft with WD40 after the dive by leaning it on a wall and spraying the top and allowing the stuff to run down the shaft which will chase any water off. I go through a small can of the stuff each season.

 

[Back2Narnia]

What do you guys think. Should i put that enclosed track on there? I am a bit hesitant to be honest. It fits pretty good tho...with some epoxy it would stay on there for good.

 

[Andrew the fish]

Enclosed track rocks. But having said that, yours is expensive gun. Carbon fiber too, glassy surface will need to be prepared for epoxy to grab on to it. It is fun to tinker, though I would be more inclined to buy another gun. Can’t have too many. My Omer Cayman ET didn’t breack 300$ mark. With all Omer’s shortcomings it is inverted trigger, cuttlefish profile, enclosed track gun. My 2c

 

[popgun pete]

If you are overpowering a shaft then an enclosed track helps as inherent rubbing losses are outweighed by gains in shaft velocity, but otherwise don't bother if the shaft can fly straight without it, i.e. without the shaft buckling under high loading from the bands. Ballasted guns with many bands would be unable to send a shaft out of them without an enclosed unless the shaft was very stiff and large in diameter, but most euroguns don't fall into that category.

 

[Back2Narnia]

I think i will test this on my other inverted Roller based on a Pathos Laser Roller 100. I like the idea of an enclosed track but you are right, i need to find a good setup for the rubbers and bearings to even out the pull. Then everything should be golden.
If that dosnt work out i will just go back to a double roller setup.

 

[Diving Gecko]

Depending on who you ask, enclosed tracks are either the bomb or they suck... I trust a guy who has done more tests on this than most and his findings are that if you want to rob your shaft of speed and the gun of performance, then do stick an ET on that gun of yours. Go search SpearQ8 on YouTube and find the test where he takes a pathos sniper 125(?) through its paces - ending up with removing the track and increasing performance quite a bit...;-)




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