SpudFiles

Jack what was the reason the spring designs wouldn't work with the blow forward bolt? Lack of travel?

Taking this example:



The bolt blows forward perfectly well, so it's ideal for semi auto, but when it's coming back, at the middle of its travel (assuming constant flow is being applied) it will once again be influenced by the air pushing it forward and will not return to its original position. In practice I've found it is possible to make it return by altering spring strength, but the cyclic rate is simply ridiculous:

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Compare this to the more reasonable rates of fire I managed to achieve by adding a "pop-off" element:

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Note also the range of rates of fire achievable by altering the flow rate, with the first example altering the flow meant it would either work as a flatulence machine or not at all.

Lot's of great ideas showing up! People are really jumping all over this. I would really like to see the magnet idea work. The idea is there.

People using these pop valves and what not, what are you guys using as reliable magazines? Gravity fed doesn't seem to work well enough from my experiance. Standard airsoft mags work with some modifications so they will shoot .177 (smaller diameter spring and BB journal size has to be changed).

Side note. Have you guys seen some of the new BBMG that will be released this year from Umarex? There is an MP5 K-PDW .177 cal. (semi auto) and the Umarex Steel Storm. Here is some links:
http://www.pyramydair.com/s/m/Umarex_St ... 2_Gun/2043
http://www.afmo.com/Umarex_H_K_MP5_K_PD ... p5kpdw.htm

The MP5 is kinda hard to find... It is in the Umarex 2010 catalog.

I just had my mind blown at the magnet calculator herehttp://www.kjmagnetics.com/calculator.asp , I was sure that the metal-magnet-metal and the magnet-magnet were the wrong way around in the calculator. As logic says that metal-magnet-metal will be the same as metal-magnet (example: if the magnetism was replaced with string they'd break at same force.. its just a longer "rope") and magnet-magnet would have combined force but no..very very strange.

I asked him if this is true and this is the response:

"Sometimes, yes! When the magnet is touching a big, flat steel plate, it can provide the same pull force as a magnet on another magnet of the same size. Of course, if your piece of steel is smaller, or very thin, it would be less.

This sounds wrong, because when you're handling them, it just feels stronger magnet to magnet. This is because, at a distance, the magnet-to-magnet case is stronger. Plug in some distance, like 0.25", and you'll see a big difference between the Case 1 and Case 3 numbers. Again, it'll be an even bigger distance if your piece of steel isn't a big, flat steel block."

So you have to visualise met-mag-met a lot different, the force exherted is divided by the parts, its not just a longer rope Still hard to grasp dont want to think about that scenario because its still going to break at one join same as a rope only breaks at one place.. something I'd have to see for myself before I believe

Also the fact that magnet-magnets exhert their force over a longer distance then just magnet-steel but is the same when touching. That means if you were to use this on a single or semi you'd actually be better off using magnet-steel.

Anyway the calculator is a valuble tool for working out what magnets do at varying distances check it out. http://www.kjmagnetics.com/calculator.asp

The idea of getting a reciprocating valve using constant airflow was a personal holy grail for many years (as the long series of prototypes attests) mainly because of the horrible inefficiency of strafer type BBMGs, which got their power not from individual projectile power but high rate of fire, the idea was to get the opposite. Admittedly now that I have access to HPA I have gone back to strafer type designs, ah well

People using these pop valves and what not, what are you guys using as reliable magazines? Gravity fed doesn't seem to work well enough from my experiance. Standard airsoft mags work with some modifications so they will shoot .177 (smaller diameter spring and BB journal size has to be changed).

The most reliable magazine seems to be a spring fed inline mag, it can work well for non-spherical projectiles like airgun pellets. The problem is limited capacity, the other option for longer firing times is using a hopper, although this limits you to spherical projectile.

I used both types with this project.

Side note. Have you guys seen some of the new BBMG that will be released this year from Umarex? There is an MP5 K-PDW .177 cal. (semi auto) and the Umarex Steel Storm. Here is some links:
http://www.pyramydair.com/s/m/Umarex_St ... 2_Gun/2043
http://www.afmo.com/Umarex_H_K_MP5_K_PD ... p5kpdw.htm

The MP5 is kinda hard to find... It is in the Umarex 2010 catalog.

We have curious to see what the mechanism is like though.

Duane31 wrote: People using these pop valves and what not, what are you guys using as reliable magazines? Gravity fed doesn't seem to work well enough from my experiance. Standard airsoft mags work with some modifications so they will shoot .177 (smaller diameter spring and BB journal size has to be changed).

I drew this up while playing with paint, trying to get a rediculous fire rate not of interest to me to try but anyways, the idea was to blow and jams away as well as force loading the magazine from a hopper. Reading through these forums this may also be a use for the wasted air it the poppit-QEV guns where the poppit air is fed over the mag in the hopper. Use it to constantly shake up the hopper and feed the mag, air aint wasted its still going out the barrel.

I'm also interested in peoples ways of joining the mag with the barrel, your working with quite tight tolerances there and it isnt as easy as it seems at least without a lathe, cant just hack into it and preserve the .03mm (in my case) clearance while giving a smooth transition.

With this sort of magazine, the BBs are automatically shaken by being pushed into the magazine after every shot.

You can see this in practice here with a clear hopper:

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This looks similar to an idea I had quite a while back, but used for a different application. It would be interesting to see magnets used more here, as they have the advantage of huge holding power with an exponentially reducing attraction as they move furthur apart.

Here is a link for the solenoid air valves I use in other guns. My next gun will utilize the same solenoid as linked along with a strobe light relay that strobes 6 times a second. The relay units can be found at automotive parts stores.

This sort of setup allows for concealment of the components in small areas. The only real draw back is having to have a 12v battery supply. I am going to check and see if an eight AA cell pack will have the amps to open the solenoid (I have been using a power wheels 12v battery which is 4 amps). The volts DC will be there, but the amps are a matter of concern.
http://www.superiorhorns.com/horn-acces ... lve-1.html

Duane31 wrote:Here is a link for the solenoid air valves I use in other guns. My next gun will utilize the same solenoid as linked along with a strobe light relay that strobes 6 times a second. The relay units can be found at automotive parts stores.

This sort of setup allows for concealment of the components in small areas. The only real draw back is having to have a 12v battery supply. I am going to check and see if an eight AA cell pack will have the amps to open the solenoid (I have been using a power wheels 12v battery which is 4 amps). The volts DC will be there, but the amps are a matter of concern.
http://www.superiorhorns.com/horn-acces ... lve-1.html

Hi Duane they are nice little solenoid valves. I think you'll have no problems drawing that current from 8 AA's http://74.125.153.132/search?q=cache:ma ... clnk&gl=au

A pulse width modulator would be a better choice then a strobe relay, it'll let you tune in the firerate and the percentage of the time its on and off during each pulse (slower fire rate, lower the duty). I have one of these http://www.rmcybernetics.com/shop/cyber-circuits.htm, I had to replace one of the capacitors with a 1uF cap to change the Hz range to about 0.75 to 150 pulses a second (its in the kHz ranges standard). There is EMI when pulsing it through a solenoid but its holding up fine.

you know you can get relays that do the same thing and are adjustable??
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this one is large as it's pretty old (built circa 1988 I guess) but there are smaller ones

alternatively I've been trying to replace this with a fully pneumatic system here
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it looks complicated but essentially it needs just a 3 way valve... but instead of manual actuation it has a port for pneumatic actuation (switching the valve)

the idea is pretty simple - first air fills the gun... gun is connected to the pilot port on the DCV... air flows from the chamebr to the pilot port on the DCV and at some point it switches the valve... once the gun fires teh main valve exhausts air from the piloting port and the DCV returns to its original position

Poland spud, that'd just be a PWM driving a relay. Useful for switching higher voltages/currents then the circuitry can handle or highly inductive loads, but with a 12v load a 12v PWM will have sharper responses. Also I dont see the ability to vary the duty on that device which would be useful to get the most power/efficiency out of each pulse. Example:, for a gun, you might want each pulse to be on 1/3rds of the time and off 2/3rds.

The PMW I linked to is quite nice and does everything you could want it too. You can even link two together to get repeating completely variable 3 shot bursts or 10 shot bursts, whatever you can imagine.

A purely pneumatic setup is of course a lot better though more difficult, bulky and harder to vary. And not to mention completely off topic both that (and pulsing solenoids for that matter) deserve their own topics.

yeah you're right.. but there are relays that can do that too...

the circuit you linked to is nice but these things are usually quite expensive... while there are lots of such relays on ebay really cheap

I bought mine for ~4$

more difficult, bulky and harder to vary

not at all... I am not really into full auto capability so I didn't bother to improve it... but essentially you only need a 3 way valve + a few fittings + a needle valve (if you want to vary the ROF)

The one I linked to does everything and I can confirm that but yep you can get them cheaper but be very wary.

Firstly they might not have EMF protection so pulsing them through a coil could damage them. The one I linked too has protection as well as an indicator. I've killed mine by pulsing into an ignition coil, it has a replacable chip if this happens (the LM.. whatever chip fries) you an just pull it out and push in a new one.

Also most dont have variable duty or have variable duty and a fixed frequency, look for two potentiometers.

Nearly all have frequency ranges far too high for use to us, they are typically speed controllers, dimmers or HHO cell supplys. The one I linked to has a socket so one can easily pull out and stick in different capacitors for different ranges (I'm sure you could ask the seller to stick whatever one you want in from the start though).

I have seen some of the nice units with adjustability - some are expensive. The automotive units are fairly cheap and work well. The draw back is that they are fixed. DOT sets the standards for the relay speed, i.e. turn signal relays have a minimum and a maximum rate standard along with strobe relays. This can be bothersome.

If I can find a relay unit that can handle 12 volts and up to 10 amps that doesn't cost an arm and a leg I'm set.