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I'm making an air cannon and I'm trying to make it automatic. How do I make the timing circuit?

I don't have all the details worked out but it should look like: http://i123.photobucket.com/albums/o290/Strid3r34/EggCannon.pngI just need to know how to make a timing circuit so that the bolt reloads (the servo should retract then detract), and then the solenoid valve is switched on for a split second (so as not to waste the air) and then reloaded again. I need it do this as long as the trigger is held down. I have no idea how to make this circuit, and I'm totally new to this so please explain in detail. pictures would help a lot.?

An Villain6 years ago
This is my idea, it is a full automatic blowgun with a revolving drum, behind the drum and on its spin axis there is a motor which is switched on before firing to get the drum up to speed, the trigger controls the high-powered pump-fan behind the barrel (at the lowest part of the drum) to send the darts flying out in a near constant stream, reloading is difficult however as you must insert a small dart into every barrel before firing, But since it uses a constant flow of air to propel light projectiles you need not worry about a solenoid valve, but for cannons, I am afraid you may need them. Also, I have included a picture of the Syringe Gun which I based my idea off of.
Syringe gun.png