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What fps do you think

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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What fps do you think

Unread postAuthor: joepage2008x2 » Sun Nov 15, 2009 9:36 am

I made a bb gun a while ago and just got it working again today, i dont have a chronograph and cant be bothered to make one until i have my next one complete. My gun can fire a plastic 0.12g bb through 2 and a half coke cans, does anyone have an idea what fps this could be.

Here is a video i made a long time ago and a few pictures. I have started a second valve it should be far more efficient than this one.

[youtube]http://www.youtube.com/watch?v=2TGLXjDSQ9s[/youtube]
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DSC00390.JPG
solenoid valve up close
DSC00392.JPG
the capacitors and the gun

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Unread postAuthor: spudtyrrant » Sun Nov 15, 2009 9:43 am

somewhere around 450 for a .2g so probably around 500-600 with the .12g the coke can test be be inaccurate tho so i wouldn't take it to heart
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Last edited by spudtyrrant on Sun Nov 15, 2009 9:45 am, edited 1 time in total.
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Unread postAuthor: rp181 » Sun Nov 15, 2009 9:45 am

clean up the capacitor bank, the stray inductance and extra resistance will be hurting you. It would also be more efficient to fire a steel cylinder, rather than transferring the energy.
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Unread postAuthor: joepage2008x2 » Sun Nov 15, 2009 10:13 am

this is only a prototype stage, many things wrong with it, i guessed the capacitor voltage, the coil size and windings. I just threw it together. I have already designed a new one, it should only need one capacitor, have far better flow and the coil will be steel, should manage up to 1000psi with ease, i will be making a semi-auto attatchment and maybe convert it to an air rifle.

May take a while before the next valve is complete as i dont have the metal to make it at the moment. Note the seal in this valve has only a 2mm hole in it and if i put my finger over the barrel there is about 20psi pressure (not enough flow) and i cannot open the valve for longer. My next valve will have a 5mm hole in the seal and open much longer. These designs are very efficient on air, i get about 6 full power shots with only about 15cc of air at about 200psi (pressure guage gone but ran at this performance before with around this pressure).

Will post a vid when i complete it, not going to show my design this time though as it will be a lot better and thought through more than the last one. I will also make a chrono to tell you the speed for the next one.
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Unread postAuthor: VH_man » Sun Nov 15, 2009 10:21 am

Very Very Cool.

All I can say is that your capacitor bank scares me... I hate to say it but its true. Clean that up a little bit, put heat-shrink over all open connections, ect. ect.

I wouldn't use this as a main valve either, but more to pilot a piston valve. It has always been my overwhelming desire to build a piston valve that can be actuated by pushing a button.

Also, If I can see from your plans, It takes ALOT of force to open your valve. I recommend taking a look at the solenoids on the tops of sprinkler valves. They are designed to be pulled slightly off their seal, and then air pressure does the rest of the work to lift it up.

Regardless of my constructive criticism, this is really one of the coolest things I think I have seen on this site. A little refinement and I can see this becoming a very effective spud gun valve.
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Unread postAuthor: joepage2008x2 » Sun Nov 15, 2009 10:36 am

thanks for the comments. the capacitors are only up to about 30V at about 47000uf so its not so dangerous, and will be lucky to get a shock, its a mess because i chucked it together and couldnt be bothered to clean it up.

i built this before knowing how proper solenoid valves worked, the main reason for this design is so i could adjust the power with more/ less voltage or capacitors, it also opens and closes faster than any valve i know of. About a month ago i found out that daystate use this type of technology for the mk3 and mk4 (made me very happy and annoyed because i thought i invented it).

I knew it would take a real lot of force to open the valve, thats why i used capacitors, i was still amazed it opened as the coil spool thingy was not magnetic just the rod inside the valve, although still very powerful, i used a bb as a spacer at the back of the valve, the power of the solenoid has crushed it.
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 15, 2009 11:15 am

Steve Harper had better watch out :) it's great that you got it to work, but now for some refinement. I would lose the 12 volt compressor (you probably aren't really getting 250 psi there) and use one from a fridge, plenty of tutorials here on how to convert one. You also have the luxury that the valve can be electronically controlled to give a particular rate of fire so some sort of autoloader would also be a good idea.

As to power assesment, have a look a the poor man's chrono for 0.2g BBs.

A small footnote, the Baikal Drozd also uses a similar mechanism, the valve
stem is built into the magazine and struck by a solenoid hammer.

Image
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Unread postAuthor: joepage2008x2 » Sun Nov 15, 2009 11:49 am

i got rid of the compressor a while ago and it said reach 250psi well until the piston seal blew (i checked it and it was about 200psi, lower than the pressure meter on the compressor), i am now using a fridge compressor(hint look at the bottom left corner of one of the pics).

Its quite a bit different from the drozd as the solenoid in mine is a pull not a push and mine just has one moving part. Also mine will offer a lot more power, im not aiming for automatic too weak, maybe semi. My next valve is either for a semi-shotgun, semi sniper or bolt-action sniper, i like power and accuracy.

i tried the poormans chrono, but only have 0.12g it manages to penetrate the bottom of the can and almost the top. I cleaned everything up and i have a bit more power for higher pressure, i get 6 average shots and one very powerful shot just with 15cc of air, i think about 250psi.

Give me a few weeks and i will have a video with the new valve and possibly semi-auto with it. And i will definately have 0.2g bbs and a chrono
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a lot cleaner, a little more power

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Unread postAuthor: Technician1002 » Sun Nov 15, 2009 12:19 pm

Due to the rate air can exit the compressor hose, I would not worry about the remaining pressure after the shot. The shot could have used most of the chamber pressure on the shot and then balanced with the remaining pressure in the hose.

If you wish to compare power, with a steering diode and a low voltage supply the valve can be fired and then held open much the same way auto fuel injectors work. An initial higher voltage is used to open it and a lower voltage is used to hold it open. A capacitor discharge is a good way to time the opening energy such as you are doing.

A comment was made regarding the inductance of the leads and such. In relation to the inductance of the solenoid, the lead inductance in air is trivial and not worth fixing.

The one thing that can be a real performance hit is the solenoid is wound on an aluminum bobbin. This conductor is the equivalent of a shorted turn to the magnet. Examine how sprinkler valve and other solenoids are constructed. DC works for slow speed valves when using a metal bobbin. High speed valves need a non conductive coil form. This should greatly improve the solenoid speed. A nylon or UHMWPE bobbin with a spiral wound iron laminate with insulation between turns under the coil is much better than a shorted turn of a solid metal bobbin for high speed operation. Study up on Iron Cores in transformers, motors, and AC solenoids for more info on this.

Using the caps for a high voltage inrush current is a good start. Well done.
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Unread postAuthor: joepage2008x2 » Sun Nov 15, 2009 2:08 pm

As you say my main problem is the aluminium bobbin, i knew this would be a problem but didnt have any other metal at the time. My new design has a steel bobbin and is slightly different to this one but should be way more efficient. The remaining pressure after the shot is still very high as i can get 6 more good shots out of it. I just hope that the valve doesnt stay open too long and waste air. The stray inductance and resistance also kept the valve open longer but was not as powerful. If the steel is a problem i can replace it with plastic so shouldnt be much of a problem.
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Unread postAuthor: Technician1002 » Sun Nov 15, 2009 8:28 pm

joepage2008x2 wrote:As you say my main problem is the aluminium bobbin, i knew this would be a problem but didnt have any other metal at the time. My new design has a steel bobbin and is slightly different to this one but should be way more efficient. The remaining pressure after the shot is still very high as i can get 6 more good shots out of it. I just hope that the valve doesnt stay open too long and waste air. The stray inductance and resistance also kept the valve open longer but was not as powerful. If the steel is a problem i can replace it with plastic so shouldnt be much of a problem.


Steel is much better than aluminum due to the much higher resistance which results in less induced current, but it is still a poor choice. The induced current in the metal bobbins not only robs power from the opening speed, they also continue after the coil current has ceased holding the valve open longer. Many delay pullin and release relays in the old telephone industry used this extensively for rotary dialing. The delay would hold the line while the mechanical dial pulsed the line. This prevented dialing from hanging up the line as dialing hung up the phone at a rate of 10 pulses/sec. The induced current in the shorting ring held the relays closed for the 100 ms dialing pulses.

The same thing happens with your design on the conductive bobbin. If you can find a non conductor for the bobbin, you will be much faster.
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Unread postAuthor: joepage2008x2 » Mon Nov 16, 2009 8:57 am

My new design is a bit different and the solenoid has a steel core (i may be able to get iron) if i change it to anything else that is not ferrous i dont think it would work or not have enough power to open the valve, it will either work as hoped or open for too long, i can always restrict the flow with an insert. Also if the current needed to open the valve is low enough i may be able to use a mosfet and an microcontoller to precisely adjust the open times, imagine programming into your rifle/bb gun what power you want, how many bb's/pellets you want it to fire and how fast, it will be a first i think.

Also note: the vid at the top of the screen is about 5 month old, the pictures are a few days old, the princepals are the same but the setup might not be. I will start putting dates on videos as people cant see my upload date if the video is inbedded in a post.

Just added a little more power, capacitor bank is about 56400uf at 30v, just powered it up to 60v so it can open at higher pressure. Pressure esimated 300psi. barrel 1ft long, bb loose fit in barrel. Fired at top of coke can with 0.12g bb, straight through top and cracked bottom. What fps do people think? its atleast 600
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