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Infinitengines "Dreamair" pneumatic speargun

Diving Gecko

shooter & shooter
Jun 24, 2008
1,350
325
138
Shanghai
Andreas replied already:)
He says the following about the power graph:


All Dreamair Unreal construction (and trigger) are made by infinitengines. The kg force is not the force of the piston. It is the force attributed to the wishbone, shaft look here: https://www.facebook.com/infinitengines/photos/a.1455848834661377/1556487181264208/?type=3&theater

The pic he is linking to is about the system I was recalling two posts back about the power redistribution to better match our physiology and here it is:
DREAMAIR CVT.JPG


But I am fairly sure I could never lift (load) a 120kg weight like that, so I am still a bit confused, haha.

BTW, I also asked what trigger he is using and it is a one he designed and made.
 

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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
3,159
638
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Australia
Everything works via the CVT System. That 120 kg on the inner cable translates with 4:1 gearing to 30 kg at the wishbone. Remember that the gearing changes continuously during the rotating of the axle. The numbers are my estimates, judging by the drum diameters.
air powered cable gun CVT system.jpg

dreamair gearing.jpg
 
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Diving Gecko

shooter & shooter
Jun 24, 2008
1,350
325
138
Shanghai
I understand 30kg at the wishbone more. Perhaps, Andreas got lost in his own numbers at some point when he quotes 120 kg at the wishbone.
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
3,159
638
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Australia
I understand 30kg at the wishbone more. Perhaps, Andreas got lost in his own numbers at some point when he quotes 120 kg at the wishbone.
English is easy to get the meaning mixed up if it is not your mother tongue. When the wishbone is at the spear shaft tab the force on the piston is 120 kg. It would be great if you could cock a gun in one gearing system and then shift to another gear cluster, say one that was direct drive, before you pulled the trigger. But that is not possible in the Dreamair as the shot is loading played out in reverse, just as it is with any direct draw speargun. The energy in the gun is the area under that graph, work or energy being force, which varies, multiplied by the travel distance in the gun. Some of the energy gets used up in friction in the gun. Unlike a normal pneumatic there is no chance of throttling, however that was the case for the alloy gun and the windows to the side tanks may have a slight effect in the carbon gun, it having three chambers instead of one oval bore.

120 kg is 264.6 pounds! About 66 pounds at the wishbone at the point you drop it onto the shaft tab. Remember as the wishbone travels forwards the force goes up because the CVT gearing is going down.
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
3,159
638
153
Australia
This diagram shows the outer cable/wishbone track in plan view as the gun shoots. Cocking the gun the process is reversed.
Dreamair wishbone track template BR.jpg

Needed to fix the muzzle section!
Dreamair wishbone track template BR.jpg
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
3,159
638
153
Australia
Just a quick calculation. 1 atm is about 14.7 psi, hence 24 atm is 14.7 x 24 = 352.8 psi. 1 psi = 0.000703 kgf/mm2 , therefore we multiply 352.8 x 0.000703 x 500 which equals 124.0092 kgf, 500 being the piston cross section in mm2.
cc.jpg
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
3,159
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Australia
Do we know if the carbon version has a pulley on the piston?
I expect that it will be a round version of this oval one and at the smaller diameter, the inner cable attaching at the front, probably with a crimp securing a loop in the cord. We know that there is also an elastic tensioning element to take the shock loading off the cord connection with the axle momentum being absorbed as it momentarily overspins at the end of travel and starts hauling the piston back against the chamber pressure. This acts as a brake on the spinning axle and drums. This way or retarding the spinning drums is actually pretty clever and stops the inner cable being cracked like a whip when the piston has hit the rear limit of travel.
Dreamair piston Oval.jpg

15123349_1836049936641263_8878646939386240773_o.jpg
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
3,159
638
153
Australia
Actually I have just been thinking about the gun's compression ratio, if it is 2.0. Any pressure in the "Dreamair" will be 1 atm above its gauge pressure as the gun has a vacuum behind the moving piston. So let us say that the start pressure is 24 atm, which means that it is 23 atm gauge. Now if we cock the gun a compression ratio of 2.0 will mean that final pressure is 46 atm, or in absolute terms 47 atm. 47 atm x 14.7 = 690.9 psi and if we multiply x 0.000703 x 500 we get 242.9 kgf. That is the force at the piston with the gun cocked. If we include the 4:1 gearing reduction then force on the wishbone is 242.9/4 = 60.71 kgf. or twice what we had before.

When the gun shoots we will be back to start pressure of 24 atm absolute. That is 124 kgf at the piston and with the gearing now 1:1 that is the force at the wishbone to start pulling on to commence for the next shot. Using the block and tackle hook loader, the one with the pulleys in the hook bodies that allows a force reduction of 2, hence we have to exert 62 kgf on the loader handles. At the end of the wishbone draw, aided by the loader's mechanical advantage and the CVT gear reduction, we only have to pull with a force of 60.71/2 or 30.36 kgf. However we had to pull for double the wishbone draw using this loader as each centimeter we move the wishbone we need to haul 2 centimeters of line through the loader handles. Makes me feel tired even thinking about it!
Energy stored charging a 23 atm gauge gun.jpg

Note that using the special loader we had to haul 200 cm of line through the loader, but halved the force effort, however we would have stored the same amount of energy as F x d is the same result as F/2 x 2 x d.
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
3,159
638
153
Australia
For a comparison we can look at the earlier graph for the 1000 mm^2 piston alloy gun.
900 joule calculation.jpg

Note that 11 atm signals that the start pressure is 10 atm gauge, 11 atm is used in the force calculation as there is a vacuum on the other side of the piston when you cock the gun. For a compression ratio of 2.0 the cocked gun pressure will be 20 atm gauge or 21 atm absolute.
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
3,159
638
153
Australia
A long time back on the Greek spearfishing website I found some tables which were all in Greek. I put one of them in the auto-translator after converting the image to text and this is how it came out after some manipulating. This table will be for the 1000 mm^2 piston equipped gun.
Dreamair Table A.jpg
 
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popgun pete

popgun pete

Well-Known Member
Jul 30, 2008
3,159
638
153
Australia
Just to give you some sense of proportion what Joules mean take a look at the table for the Aquatech "Black Sea" hydropneumatic hydropump gun.
Aquatech Black Sea Table.jpg

The Joules here are what came out as I think that they were calculated using the velocity and mass of the spear.
 
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