SpudFiles

I am new to Spud Gun and I want to build an AT4 looking air cannon to use in airsoft game. My plan was to fire different type of ammo. Such as spud, smoke grenade and full loads of BB (shot gun). My plan was to charge it with bike pump only, didn't plan to use compressed air such as co2.

The approximately volume of the air tank is

(3.14 x 7cm x 100cm) = 2198cm3 or 2198ml

2198cm - Barrel volume

2198cm - (3.14 x 5cm X 50cm) = 1413cm3 or 1413ml


Question
1. Is there too much power to release all the air once with that volume :bounce:
a. Should I make a semi switch? so that I can shoot twice or more instead of releasing all compressed air at once
b. Should I increase or decrease barrel length?
2. Should I add a smaller or bigger Qev with another so that I can choose to release more or less air ?
3. is the air tank too big?
Please feel free to give me any advise

The configuration you have there, if I've read the intent of your diagram right, cannot fire, as the QEV is incorrectly connected. I'd recommend looking at the piston valves explanation topic, as QEVs work on the same principle as barrel sealing valves.

The approximately volume of the air tank is

The volume of a cylinder is pi * r^2 * h, not pi * d * h. The correct volume is closer to 2850 ml.

1. Is there too much power to release all the air once with that volume :bounce:

Yes and no, depending on why you're asking. A ludicrously large chamber won't usually actually be an actual hazard (beyond being a threat to hearing or if you drop it) or stop the launcher working, but using that much air all at once will have no benefit and will just be a load of wasted effort.

If you're intending this for use as a launcher for use in airsoft scenarios, you really want to use the smallest practical amount of air per shot, as you really don't want to spend four minutes pumping it up every time.

That may mean one smaller chamber or working out how to get several shots out of one pressurisation. Personally, I'd probably recommend the first, as it's mechanically much simpler and means the launcher can be completely unpressurised whenever you load it. (Trying to muzzle load a launcher that's still pressurised for several more shots strikes me as a potentially hazardous loading operation).

b. Should I increase or decrease barrel length?

Increasing it would allow more efficient use of the air in the chamber, but ultimately the length should really be defined by what's going to produce a safe muzzle velocity for use in airsoft games.

2. Should I add a smaller or bigger Qev with another so that I can choose to release more or less air ?

I'm not sure what you mean by this.

3. is the air tank too big?

See above answers. Three litres isn't massive if you want to get several shots out of it, but for one shot it would be excessive.

I don't think you quite understand how a QEV works

vng21092 wrote:I don't think you quite understand how a QEV works

Thank you for your helpful information. What kind of valve do u recommend to put in my cannon? How can I control the amount of air it releases? can a suitable valve solve all that problem? Do you think it can shoot a spud 50m away in 45 angle with current design?

vng21092 wrote:I don't think you quite understand how a QEV works

Sorry I a bit confuse since I am a nub. Isn't that diagram a coaxials cannon design? coaxial cannon work like a qev?

vng21092 wrote:I don't think you quite understand how a QEV works

Thank you for your explanation. I meant what kind of valve should I use? what kind of valve is suitable if I want to control the amount of air it release. I want to release more pressure when the target is further and less when its neare r and to also shoot a few times instead of one if the target is too close.

Coaxial cannon work like a qev?

It's the same concept, on a smaller scale.

I meant what kind of valve should I use? what kind of valve is suitable if I want to control the amount of air it release. I want to release more pressure when the target is further and less when its nearer

A sprinkler valve would do the job. As to controlling the impulse, that's a bit trickier.

and to also shoot a few times instead of one if the target is too close.

If you use the sprinkler valve as-designed with electric actuation, it would be possible to actuate it with a momentary switch that would only give you a brief burst of air. Not sure if your plan is realistic with bike pump pressures and a reasonably sized chamber though.

2. Should I add a smaller or bigger Qev with another so that I can choose to release more or less air ?

I'm not sure what you mean by this.

Thanks Ragnarok for so much detail explanation. I meant what kind of valve should I use. Should I just put 2 ball valves together a smaller one and a bigger? any suggestion? what would an expert like you do?

A sprinkler valve would do the job. As to controlling the impulse, that's a bit trickier.

Where can I buy a sprinkler?? Will they fit in my 7 cm tube??