# Electric Paintball gun

#### Serj

I am making an electric paintball gun. Nothing fancy just analog. For the paintball guun to work a solenoid turns on when a normally open push button is pushed. The power goes on breifly, then off. Then another solenoid turns on , then off. That solenoid is hooked up to a valve that released pressurized air, the length of time the valve is open and the pressure of the tank determines how fast the ball goes. The circuit needs to compensate for a loss of pressure, ie leave the valve open longer. The two solenoids must be sinked up so that one is off while the other is on. What would that circuit look like?

here is a poorly drawn diagram of the paintball gun http://putfile.com/pic.php?pic=7/19515191068.jpg&s=x2

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#### berkeman

Mentor
Why do you need two solenoid valves? It seems simpler to just use the one that is at the output of the pressurized storage tank.

And a simple way to compensate for changes in pressure in the storage tank would be to use an optical sensor placed part-way down the barrel of the gun, and use the ball passing that point as the signal to close the solenoid. You'd have to experiment some to see how far down the barrel you want the sensor, but maybe start at about half-way to see how that works.

So pulling the trigger opens the pressure solenoid valve and turns on the optical sensor circuit in the barrel. The paintball passing the sensor closes the pressure solenoid valve. The trigger has to be released before the next sequence/shot can be performed. You should also put a max allowed open timeout on the pressure solenoid, in case the pistol is fired with no ball in the chamber.

#### Serj

thank you for replying. To answer your question, one solenoid closes the hopper off from the barrel so air doesnt go into the hopper when the gun fires. I want something that is not too expensive, I only assumed that timing the valve would be the cheapest way of doingthings. Does the optical sensor calculate the speed of the ball?

#### berkeman

Mentor
What's a hopper? I've only played paintball twice, and that was long ago with low-tech rented guns.

The theme behind using an optical sensor in the barrel is to use it to adjust the open-time of the solenoid so that you get about the same push down the barrel, even as the pressure in the tank is dropping from shot to shot. I wasn't thinking of speed sensing, although that's not a bad 2nd order variable that you might want to add into the calculation of how long to keep the valve open. I was thinking that as the forcing pressure dropped, the ball will be slower to move down the barrel, so a 1st order correction would be to hold the valve open for the extra time it takes the ball to get down to some point x in the barrel. I guess for best accuracy, you will want to figure out the best way to maintain a consistent muzzle velocity, so you will need to do some calculations to see how much correction you can get from just sensor position x alone, and what the optimum x is. Then maybe a good 2nd order correction would be to do 2-3 sensors, and use them to give you some velocity and position info.

Fun problem. I still don't get the hopper thing, though. If the hopper is an important intermediate pressure storage chamber, then it would probably just be easier to put a pressure sensor in there, and calculate the final valve opening duration from that. -Mike-

#### GENIERE

berkeman said:
...And a simple way to compensate for changes in pressure in the storage tank would be to use an optical sensor placed part-way down the barrel of the gun, and use the ball passing that point as the signal to close the solenoid. You'd have to experiment some to see how far down the barrel you want the sensor, but maybe start at about half-way to see how that works.
Clever!

...

#### Serj

A hopper is just a plastic case above the gun were paintballs are stored before firing. http://www.moodypaintball.com/pages/tech/diagram.htm there are two green paintballs in the diagram.One is in the feed neck between the hopper and the bolt.

Ok, now I know what you meant with that optical sensor. It would be good but also expensive (i'm assuming it's expensive, if i'm wrong please correct me). As an alternative to sensors I was thinking about using an equation to estimate how long to leave the valve open. How would I make the valve open for X time with a circuit? (capaciters?)

#### Mk

Optical sensors are so cheap that Lego sells them in their Mindstorm kits, and they're put in every optical mouse. I couldn't help you on finding them though.

#### Serj

how would the circuit work? The length of time the barrel is open must be adjustable, would a rheostat do the job or should I use something else?

#### Danger

Gold Member
Serj, I appreciate that one has to do things one's own way. You wouldn't believe some of the stuff that I've come up with just to be different. As one who has repaired/rebuilt paintball markers for a living, I seriously think that the electrical approach will be far less efficient than what is currently done with time-tested mechanical systems. A full-auto marker can fire over 10 balls per second, and is far less susceptable to physical hardship than an electrical/electronic one would be. The regular ones are very prone to screwing up when a ball explodes before launch (very common), but a couple of no-ammo shots can clear them; something with an optical sensor in the barrel would shut down completely when the eye gets painted over. The only two electrical things that seem appropriate to me are the established motor-stirred hoppers and maybe a solenoid trigger that would still set off a normal mechanical chain of events. If you're determined to do it according to your initial plan, just be aware that it won't give you any advantage in a game.

#### Serj

I've been trying to design a mechanical one for years. None of my designs were any better than the stuuf that's out now so I decided to go electric. My design for electric is only a few cheap peices connected to a circuit board. I agree that optical would not work if a ball exploded in the barrel. Instead I was thinking of using timing to determine when to open/close the valves and solenoid which is were my problem is. I do not know how to design a curcuit board to carry out the function of adjustable timing.

#### dlgoff

Gold Member
Serj said:
I do not know how to design a curcuit board to carry out the function of adjustable timing.
I would suggest looking into the 555 timer integrated circuit (or 556 duel timer in your case?). You will need to look into how to use a transistosr on the timers outputs for driving the solenoids. The timers use resistors to set the time. You can use varable resistors so you can adjust the timing for best action.

Regards

#### Danger

Gold Member
Serj said:
Instead I was thinking of using timing to determine when to open/close the valves and solenoid which is were my problem is. I do not know how to design a curcuit board to carry out the function of adjustable timing.
I'm afraid that it's out of my league, then. I do wish you the best with your endeavour, and keep us posted as to your progress. I can't help in this situation, but I'm very interested in how it turns out. Even if you don't figure that it's worth a post, at least PM me to let me know what happens.

#### berkeman

Mentor
Great info from Danger. So it sounds like a mechanical technique could work, maybe just the compensation for the decreasing gas reservoir pressure isn't part of most existing mechanisms? One first step might be to just fixture the place where the tank screws into the gun with a mechanical pressure gage so you can read what the pressure is. Then figure out a way for a thumbscrew-type control to change how long the mechanical pressure valve opening/pulsing circuit stays open. Once you have those hooks, you can do some calibration shooting, and make yourself a chart that you can use in the field to tune the mechanism based on the pressure readings. You shouldn't have to tune too often, especially at first with a fresh tank.

Having the thumbscrew control over the shot strength seems like it would be handy anyway, since you could turn down the power for close-in rapid fire shooting, and turn it up for longer range shots.

#### dlgoff

Gold Member
berkeman said:
Great info from Danger. So it sounds like a mechanical technique could work, maybe just the compensation for the decreasing gas reservoir pressure isn't part of most existing mechanisms? One first step might be to just fixture the place where the tank screws into the gun with a mechanical pressure gage so you can read what the pressure is. Then figure out a way for a thumbscrew-type control to change how long the mechanical pressure valve opening/pulsing circuit stays open. Once you have those hooks, you can do some calibration shooting, and make yourself a chart that you can use in the field to tune the mechanism based on the pressure readings. You shouldn't have to tune too often, especially at first with a fresh tank.

Having the thumbscrew control over the shot strength seems like it would be handy anyway, since you could turn down the power for close-in rapid fire shooting, and turn it up for longer range shots.
He said he has been working on mechanical designs for years and now he wants to do it with electronics. I believe his idea of timing solenoids with a simple circuit is the way to go.

Regards

#### Serj

i'm going to use the equation F=(V2-V1)/t*m to determine how open the valve must be to reach the desiredfinal velocity, F being the force of the pressurized air determined by how open the valve is and how much pressure is in the tank. The problem is that the time and V2 vary with force.

#### berkeman

Mentor
dlgoff said:
He said he has been working on mechanical designs for years and now he wants to do it with electronics. I believe his idea of timing solenoids with a simple circuit is the way to go.

Regards
Fair enough. I don't know how much energy it takes to snap open a solenoid pressure valve, though, so I don't know how practical the battery size would be. Does anybody know what solenoid valve would typically be used for an application like this, and what the response time would be? It seems like the bias spring would have to be pretty stiff to reliably re-seal the valve, and to make the closing time quick. So the energy per shot could be fairly substantial, and the continuous output current requirements for the battery could be pretty high with the 10 shots per second in rapid fire mode. The solenoid would probably be a 12V coil (?), with a coil current of a few amps during each pulse (?). Maybe he could stack a few radio-control-car NiCd high-current batteries to get enough energy for a few gas cylinders, or combine a smaller battery pack with each gas cylinder as a module or something....

I guess that using battery energy for the valve will save some gas -- maybe the OP will do the calcs to see how big the battery needs to be, and how many more shots per gas cylinder he'll get using the batteries for the gate valve instead of some of the gas pressure energy.....

#### Danger

Gold Member
I'm going to pop back in just for a bit of clarification. The strength of the shot is determined by the setting of the pressure regulator, not the length of time that the valve stays open. In fact, the valve opening is in a small way determined by the pressure as well because higher pressure can cycle it faster. When the gas pressure drops too low, the bolt doesn't fully return and the thing goes full-automatic. (That's not as much fun as it sounds, because the balls launched in that manner have no 'ooomph' behind them and clog up the barrel. It's like trying to fire a bullet with just a primer and no powder in the case.)
If I remember correctly in regard to real firearms, electric triggers usually don't need too much battery power because they utilize a capacitor for the high-energy discharge. I don't know enough about electronics to say if that would be appropriate in this case or not. My personal preference over a solenoid in this case would be a length of 'Biometal' or similar shape-memory metal if the driver circuit can be made small enough. Because it releases more energy reforming than it takes to deform it, you can use counteracting pieces rather than needing a return spring.

#### dlgoff

Gold Member
This mignt be a good place to start for solenoid valves. I'm sure there are very small ones that might work.

#### Serj

Serj said:
i'm going to use the equation F=(V2-V1)/t*m to determine how open the valve must be to reach the desiredfinal velocity, F being the force of the pressurized air determined by how open the valve is and how much pressure is in the tank. The problem is that the time and V2 vary with force.
That equation does not work. The valve needs to shut off after the ball has left the barrel, but that equation does not contain the length of the barrel.

#### Danger

Gold Member
Serj said:
That equation does not work. The valve needs to shut off after the ball has left the barrel, but that equation does not contain the length of the barrel.
I just thought of something here, but I don't know if it's practical. If your primary requirement is to note when the ball leaves the barrel, how about just integrating a pressure transducer in the rear of the chamber? A sudden pressure drop would indicate that the barrel is clear.

#### Serj

Danger said:
I just thought of something here, but I don't know if it's practical. If your primary requirement is to note when the ball leaves the barrel, how about just integrating a pressure transducer in the rear of the chamber? A sudden pressure drop would indicate that the barrel is clear.
That is a very good idea , but if the equation does not factor in the length of the barrel, it will be unknown how much to open the valve so that the ball leaves at the right speed.

#### Danger

Gold Member
Serj said:
it will be unknown how much to open the valve so that the ball leaves at the right speed.
How about just using an adjustable timer and trial-and-error? We always just chronographed the things and tweaked them to 300fps with the pressure regulator screw. Since most barrels are easily removable for cleaning, this would allow you to change lengths if required. (Short for heavy foliage, long for sniping, etc..)

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