Infinitengines "Dreamair" pneumatic speargun

[Diving Gecko]

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:

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.

 

[popgun pete]

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.

 

[Diving Gecko]

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.

 

[popgun pete]

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.

 

[popgun pete]

This diagram shows the outer cable/wishbone track in plan view as the gun shoots. Cocking the gun the process is reversed.

Needed to fix the muzzle section!

 

[popgun pete]

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.

 

[Diving Gecko]

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.
View attachment 54756

Do we know if the carbon version has a pulley on the piston?

 

[popgun pete]

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.

 

[popgun pete]

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!

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.

 

[popgun pete]

For a comparison we can look at the earlier graph for the 1000 mm^2 piston alloy gun.

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.

 

[popgun pete]

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.

 

[popgun pete]

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.

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

 

[Diving Gecko]

Just stumbled upon some tests I did a little while back about how much power bands drop over time. But what is interesting to me now is that I measured a Primeline Small ID 14.2mm band takes around 24.6kg to load with a stretch factor of four. That's about 50kg per band. Now, on my Pathos 100, I have those bands stretched to about 3.7 which gives about 5% less power but that's also pretty much around what I can load.
I am not a big guy and I am fairly sure I couldn't be loading a Dreamair with 120kg as starting force. Even if it drops to half that at the end.
Perhaps the loader came around at some point when Andreas realized that his bald Greek God Of Loading (see post #301 above) was not representative of the average spearo? Or maybe it is, and I am only half as strong as the average spearo. Could be

I am honestly still not sure what to think about the pulley loader, yet. On one hand, I made one myself to be able to "cheat" when loading my long airgun - and I think it showed great promise - but on the other hand, it does take a little bit of the shine off of the Dreamair for me if you have to use it to get the gun to really sing. But as I said, I made one, so perhaps I am a hypocrite, haha.
Ideally, the Dreamair should outshoot anything in its size class without needing a loader. But I am beginning to think that's hoping for too much with e.g. double banded guns and pulley rollers already having more than just the one loading step of the Dreamair. But using the pulley loader might end up taking longer than loading two bands, perhaps even three bands (or a pulley loader with three loading steps) and that might become an issue for some.

 

[popgun pete]

I will wait until I get my hands on one, personally I think that they may be the greatest invention since sliced bread. Power from a pneumatic gun can come from a big piston, a dry barrel gun with a big area piston represents a loading problem, but in the "Dreamair" that big piston and the shaft drive are separated by using the winching cable system, somewhat like an aircraft carrier catapult which are steam driven.

 

[Diving Gecko]

Yeah, I guess the proof will be in the pudding and we just have to wait and see.
Right now, I imagine it is actually a very sweet gun as a single loaded one for the reef. I am thinking that one advantage of the CVT is that the power will be delivered in a more smooth and gradually increasing fashion during the shot which might mean better shaft stability, even less recoil and perhaps better overall efficiency. It might be a real sweet scalpel to wind and shoot.
This progressive power application really sets it apart from any other gun out there, at least on paper but let's hope there is a real world advantage to it, too.
In larger sizes or if you really need the max power and hence, the double loader the Dreamair may start facing stiffer competition from other 'multi-loader' guns.

 

[popgun pete]

A longer "Dreamair" for launching long shafts could go to the double axle version. Basically that gun uses half of the piston movement for the first wishbone and the second half for the second wishbone. Therefore for a 20 atm start pressure you would have a final pressure of 40 atm with the piston fully advanced in the gun. The energy or power increase would be the longer distance in the barrel that the piston travels. The final pressure after the first wishbone draw would be 26.6 atm.

.

 

[popgun pete]

Here is a diagram estimating a gun of 110 cm wishbone draw with a piston travel about 34.375 cm based on a multiple of 3.2 with respect to the relation between piston travel and wishbone travel. Start pressure is 23 atm gauge or 24 atm absolute.

Note that the wishbone energy graph will not necessarily be this shape due to the gearing changes as the wishbone moves along the gun. Pulling the piston forwards in a "Dreamair" as you load the gun the pressure increases in the pneumatic chamber, hence force on the inner cable goes up, but counteracting that the gearing provided by the ratio of drum diameters at any given instant increases due to the outer drum getting bigger as the cable moves inwards on the drum (towards the barrel) while the inner drum is getting smaller as it winds cord on towards its narrow end.

 

[foxfish]

So Pete, you “are” going to buy one?

 

[popgun pete]

So Pete, you “are” going to buy one?

Yes. An alloy gun, but if they don't proceed then a carbon fiber, although I am more familiar with alloy and wood as that is what all my band guns are constructed from. Only carbon fiber gun that I own is the rather heavy "Urukay", purchased only because it was an absolute bargain!

Paid under 900 bucks for it as they are slow sellers and stock has to be moved. Very well made example, flawless!

 

[Zahar]

I would wear a carbon shrink tube!