need advice for making a very custom water gun

Build a homemade water gun or water balloon launcher and tell us about it.
neogeo
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need advice for making a very custom water gun

Post by neogeo » Mon Apr 26, 2010 4:51 pm

I think I'm posting this in the right place, but if I'm not, could a mod please move it to the right place? Thanks. I'll also preface this by saying that I have experience in working with electricity, servos, and microcontrollers. I do not, however, have much experience modding water guns, much less building them from scratch, which is why I'm here now.

Also, I apologize for the extremely long first post.

I'm in the middle of the research phase for a fun little project that I wanted to try building, and it seems like you guys should definately be able to help me out. Essentially, I want to build a fully automated water gun that can be carried in a backpack, that would shoot water out of a nozzle mounted to either my wrist, the palm of my hand, or possibly my finger, depending on which looks better. I have most of the theory worked out already, but i still have a few questions that I need answered.

Here's how I planned to do it. I was going to build a custom water tank that would be stored in the backpack out of PVC tubing. This would be pressurised by a battery powered air compressor that would also be stored in the backpack. As luck would have it, the hardware store I work at sells these car jumper/tire filler kits that are completely self contained for a very reasonable price. The air compressor only goes to 100 PSI, which from what I've read is just about perfect for a water gun like this. Anyway, the water tank would connect to a seperate pressure chamber, just like a CPS water gun, which would also connect to two water lines that would run out of the backpack, along my arms, and down to my hands. Each of my hands will have an actuator that will control water flow out of each nozzle seperately. All of the electrical components will be controlled through a microcontroller.

Now we all know what happens when you mix water and electricity, so I do have some safety measures in place. All of the electrical components in the backpack will be sealed in plastic. This plastic bag will have a small air inlet hose so the compressor works properly, an air outlet hose that will be attached to the tank, and a very small opening for any wires that have to run in or out of the bag. The actuators on my hands, as well as the valve releases will be bagged as well and sealed around the openings. This whole project is mostly for proof-of-concept work and will likely never see an actual water war. Maybe if i make a Version 2 at some point.

Now here's where I'm stuck. I don't want the compressor running all the time, but i want it to run consistantly when I need it. All I need it to do is fill the pressure chamber after each shot. I have a couple of ideas on how to do that, but I wanted input before I tried to impliment one of them. One of these ideas was running a couple of wires to the pressure chamber to act as a switch. Secure a small bit of metal to the inside of the outter shell of the pressure chamber to act as a spring, and when the pressure chamber is full, it will depress the spring, completing the circuit and shutting off the compressor. My other idea was having the microcontroller run the compressor for X amount of time after every shot. X being however long it would take to fill the pressure chamber. I'm completely open to other ideas though, so if you have a better one, then please post it.

My other problem has to do with triggering the water flow. I'm not sure what the best way to go about it would be. My first two ideas were to either have a servo that turns a screw that pinches the line shut or take the trigger mechanism from an existing water gun and run the water out lines through that. The problem with the first idea is that I wanted to have "clean" shots, where there's no trickling of pressure before or after the shot. That's also why I decided on a pressure chamber for this project. While I haven't tried yet, I'm worried that a servo would not be able to open and close the line fast enough to avoid that problem. As for the second idea, I'm a bit worried about the overall size of the mechanism and the fact that I'd have to essentially buy a gun just to get the firing mechanism out of it. I could place the firing mechanism in the backpack, but I don't know if that would produce a delay between when I use the actuator and when the water comes out of the end of the nozzle. Again, I'm open to any ideas on that front.

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cantab
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Re: need advice for making a very custom water gun

Post by cantab » Mon Apr 26, 2010 5:12 pm

neogeo wrote:Here's how I planned to do it. I was going to build a custom water tank that would be stored in the backpack out of PVC tubing.
That sounds entirely viable.

This would be pressurised by a battery powered air compressor that would also be stored in the backpack. As luck would have it, the hardware store I work at sells these car jumper/tire filler kits that are completely self contained for a very reasonable price. The air compressor only goes to 100 PSI, which from what I've read is just about perfect for a water gun like this.
The issue is not just pressure, but flow rate. How long does it take to inflate a car tyre? It'll probably take a similar length of time to pressurise the blaster.

Anyway, the water tank would connect to a seperate pressure chamber, just like a CPS water gun
I am not sure why that is necessary. Just fill the tank about two/thirds with water and then compress the air in it.

Now we all know what happens when you mix water and electricity
If the water is fresh (not salt) and clean, and the voltages involved are extra-low (like 12 volts), not much. IIRC when Mythbusters tested escaping from a sinking car they found the windscreen motors still worked when the car was on the bottom of the swimming pool. Still, better safe than sorry.

My other problem has to do with triggering the water flow. I'm not sure what the best way to go about it would be. My first two ideas were to either have a servo that turns a screw that pinches the line shut
Pinch valves are a lousy choice, avoid.

I could place the firing mechanism in the backpack, but I don't know if that would produce a delay between when I use the actuator and when the water comes out of the end of the nozzle. Again, I'm open to any ideas on that front.
It's better to have the firing valve close to the nozzle. The delay will only occur if there is air in the hose, which will be the case on the first shot, and afterwards if water leaks out of the nozzle. (It will stay in a small nozzle, but flow right out of a big one). However, firing valves aren't usually small.
They're not the best for performance, but sprinkler valves actuate electronically.

Finally, I will say that there already exist devices that do exactly what you want to do. Backpack sprayers, typically used for spraying chemicals in gardens. Most have a hand-operated lever pump, but some (more expensive) are battery-powered. You may want to make modifications for performance - increasing the tubing diameter and changing the nozzle and firing valve should help a lot. I have a smaller, non-backpack model which is not bad - the stream size and range are XP-class, but the shot time is an impressive over two minutes solid.
I work on Windows. My toolbox is Linux.
Arsenal:
Super Soaker: XP215, 2xXP220, Liquidator, Aquashock Secret Strike M(odded), Arctic Blast M, CPS1200, CPS2100, SC Power Pak, 3l aquapack, 1.5l aquapack
Water Warriors: Jet, Sting Ray M, Shark, Argon M, Tiger Shark, PulseMaster
Others: Waterbolt, The Blaster, Storm 500, Shield Blaster 2000, generic PR gun, generic backpack piston pumper (broken), 3l garden sprayer M, 10l water carrier:

neogeo
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Re: need advice for making a very custom water gun

Post by neogeo » Mon Apr 26, 2010 6:17 pm

cantab wrote:The issue is not just pressure, but flow rate. How long does it take to inflate a car tyre? It'll probably take a similar length of time to pressurise the blaster.

I am not sure why that is necessary. Just fill the tank about two/thirds with water and then compress the air in it.

The reason I want to go with a PC is because a tank alone gives me no indication of pressure. With a PC, I know it's full and ready because the compressor has forced enough air into the tank to push the right volume of water into it to fill it up. Not only that, but it makes wiring some sort of sensor or switch to regulate the compressor much easier. Not only that but it should take far less time to fill a PC than it should to pressurise a tank repeatedly. After the initial pressurisation of the tank, it should take only a few seconds to fill the PC for the next shot, in theory.
If the water is fresh (not salt) and clean, and the voltages involved are extra-low (like 12 volts), not much. IIRC when Mythbusters tested escaping from a sinking car they found the windscreen motors still worked when the car was on the bottom of the swimming pool. Still, better safe than sorry.

Yeah, better safe than sorry. I wouldn't want to have the actuator on my hand get hit with water and short out or something. Really, my biggest electrical concern is the compressor/battery. IIRC, the specs for the electrical output of the battery were something in the neighborhood of 12V at 14A, which is much, much more than enough to ruin my day.
Pinch valves are a lousy choice, avoid.

It's better to have the firing valve close to the nozzle. The delay will only occur if there is air in the hose, which will be the case on the first shot, and afterwards if water leaks out of the nozzle. (It will stay in a small nozzle, but flow right out of a big one). However, firing valves aren't usually small.

Good advice. I'll have to do more research to find a good firing valve.
Finally, I will say that there already exist devices that do exactly what you want to do. Backpack sprayers, typically used for spraying chemicals in gardens. Most have a hand-operated lever pump, but some (more expensive) are battery-powered. You may want to make modifications for performance - increasing the tubing diameter and changing the nozzle and firing valve should help a lot. I have a smaller, non-backpack model which is not bad - the stream size and range are XP-class, but the shot time is an impressive over two minutes solid.


Good thinking there. I never thought to look into any sort of garden sprayer. The store I work at sells the hand pumped ones, but I should be able to use the something from one of those. I'll look into that.

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soakernerd
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Re: need advice for making a very custom water gun

Post by soakernerd » Mon Apr 26, 2010 7:59 pm

Wait, you're relying on the compressor to force air into the reservoir, which will then force the water into the pressure chamber? If so, you can improve the mechanism quite a bit.

First off, you'll need a check valve between the CPS chamber and the backpack, to keep the water in the PC.

Second, I would recommend an electric pump for water, rather than air. the water pump can pump the water directly into the PC, rather than relying on air. since air is compressible, it will compress rather than pushing the water into the CPS chamber. In order for this design to work, the rubber in the PC must expand at a lower PSI than the compressor can work at.

If you do go with the compressor, I highly recommend a SuperCannonII-style piston in the reservoir. This will separate the air from the water and ensure that you are only pumping water into the PC.

If you build an SCII-type mechanism, however, you might as well just build a device to depress the piston, and rely on that for pressure, rather than air.

The automatic shut-off switch is pretty easy. Someone on NerfHaven posted a Write-Up for the Magstrike, which uses a bladder similar to a CPS chamber to store air.

Hope I helped, ;)

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C-A_99
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Re: need advice for making a very custom water gun

Post by C-A_99 » Mon Apr 26, 2010 8:32 pm

You don't need more than one pressure chamber. If you want to have a small pressure chamber, then it's best to leave the main reservoir unpressurized and to have a motorized pump move water to that chamber. The problem with this is that you'll have to dig around for such a pump, or build one. A pressurized reservoir type of backpack keeps things simpler, but the problem is that as the water drains, more and more air will be needed to replace it and thus pumping to full pressure will take longer. Nonetheless, this design can still work by using a pressure gauge. The gauge would be responsible for activating the pump and indicating the pressure to the user.

Shooting projectiles is another story. The reason you would have two pressure chambers is so that one acts as the main air storage. The second pressure chamber is for controlling air bursts to shoot each projectile, ensuring that each projectile fired recieves the same pressure of air.

neogeo
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Re: need advice for making a very custom water gun

Post by neogeo » Tue Apr 27, 2010 8:47 pm

Well, I have good news, the store I work at does indeed sell battery powered garden sprayers. The bad news is I'd almost feel like I'm cheating by using one though. I'm a DIY enthusiast(who here isn't, really), and half the fun of building your own water gun is building it from scratch, not taking a couple of premade things and sticking them together in the proper order, right? I know that I can fall back that sprayer if I can't solve this with a custom job, so at least there's that.

Soakernerd, you mentioned that a PC must expand at a lower PSI than the compressor can put out, right? Does anyone know what PSI a stock PC needs to inflate? That's one value I just realized I would need and totally forgot to find out.

Assuming that the PC will inflate at a pressure lower than 100 PSI, I'd like to explore the original concept a bit further. The Supercannon II looks really cool, but it seems like it'd need an unusually large or complex series of tube tanks to be able to fire for more than a few seconds. If that's all being held inside a backpack, it doesn't seem very feasible. As far as a water pump, I don't even know what sort of output would be needed by a water pump for this sort of application. I had initially decided on an air compressor because I knew exactly what the output would be and I knew it would provide me with consistant results assuming it would work properly. If need be, I can replace the 100 PSI compressor inside the battery/compressor combo pack with a 250 PSI compressor that my store also sells for a little bit more money. I read that PVC generally has a pressure limit of 220 PSI, so while that compressor could present a slight pressure hazard, it should be mitigated by the filling control mechanism, which should trigger and stop the compressor before it ever reaches such high pressure. I'm not worried about how long it takes to pressurize the chamber, since I'm not looking for instant rapid-fire shots anyway.

I have an unrelated question, by the way. Since at least a couple of you guys seem to know a bit about air guns, I figure I could ask this here. I have a seperate project that I'm working on that needs a valve connected to an air hose. This valve is apparently very special, because it needs to be able to go from fully closed to fully open in less than one turn, prefferably less than half a turn. Does anyone know where I might find such a valve? It doesn't necessarily need to be for air only, as long as it's air tight. I plan on having this valve hooked to a servo that will open and close it, so the easier it is to open, the better.

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soakernerd
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Re: need advice for making a very custom water gun

Post by soakernerd » Tue Apr 27, 2010 8:59 pm

Does it need to be a ball valve? could you use a solenoid? I believe that they use electricity to open. A ball valve opens by rotation. a quarter turn (90 degrees) opens it fully. however, they are not the best for airguns, as they open over a longer period of time.

here is a link to a selection of solenoid valves: CLICKY

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cantab
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Re: need advice for making a very custom water gun

Post by cantab » Tue Apr 27, 2010 10:49 pm

The 250psi compressor won't necessarily be better. In fact it might be WORSE, if it pressurises more slowly.

I believe a stock CPS chamber would be about 30-50 psi depending on the blaster.
I work on Windows. My toolbox is Linux.
Arsenal:
Super Soaker: XP215, 2xXP220, Liquidator, Aquashock Secret Strike M(odded), Arctic Blast M, CPS1200, CPS2100, SC Power Pak, 3l aquapack, 1.5l aquapack
Water Warriors: Jet, Sting Ray M, Shark, Argon M, Tiger Shark, PulseMaster
Others: Waterbolt, The Blaster, Storm 500, Shield Blaster 2000, generic PR gun, generic backpack piston pumper (broken), 3l garden sprayer M, 10l water carrier:

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martianshark
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Re: need advice for making a very custom water gun

Post by martianshark » Wed Apr 28, 2010 1:15 am

Why not use a garden hose nozzle? Then you could easily operate it with one hand.

neogeo
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Re: need advice for making a very custom water gun

Post by neogeo » Wed Apr 28, 2010 2:34 am

soakernerd wrote:Does it need to be a ball valve? could you use a solenoid? I believe that they use electricity to open. A ball valve opens by rotation. a quarter turn (90 degrees) opens it fully. however, they are not the best for airguns, as they open over a longer period of time.

here is a link to a selection of solenoid valves: CLICKY


Those actually look like they might be perfect firing valves for the water gun... except for the fact that I just noticed that the cheaper ones seem to average ~$75-$85 a piece. Yeah, that's about half the price of both of these projects put together. :eek:

As far as the air valve, the thing is that I need it to control the flow of the air. Not only do I need it to open and close with as little rotation as possible, but I need it to essentially regulate the air flowing through it. It needs to be smooth, going from closed to full blast. The air won't be at a very high PSI, so it doesn't need to be robust or anything. Oh, one final bit of specification: the line the air is traveling through is very small. I believe it's 1/2" OD fuel line. I told you this was a special valve I needed. So far, I've been experimenting with a screw valve. Turn the screw and it pinches the line shut. The problem I'm finding though is that the screw isn't very precise in how much it's pinching the tube, and I'm getting inconsistant pressures when I turn the screw to the same spots.

cantab wrote:The 250psi compressor won't necessarily be better. In fact it might be WORSE, if it pressurises more slowly.

I believe a stock CPS chamber would be about 30-50 psi depending on the blaster.


I'll have to look at the documentation for both and see is the volume output is listed for both of those. I'm pretty sure the 100 PSI compressor is labeled as "high volume", but I don't know if that means anything. I might end up not needing an air compressor anyway because a friend of mine at work gave me an idea. I might be able to find a suitable low power fluid pump in a go cart fuel pump. He said that those run on a very similar power output to what the compressor runs on, so it should be an easy match as a fluid pump. I'll have to do some research and see what sort of outputs such pumps can achieve.

martianshark wrote:Why not use a garden hose nozzle? Then you could easily operate it with one hand.


Because both hands will have water nozzles on them, obviously. I'm also going for a minimalistic look with this thing, so that most people would just see a backpack and a line running out to my hand. A small button would be much more easily concealed, assuming I can find a good way to trigger everything.

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martianshark
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Re: need advice for making a very custom water gun

Post by martianshark » Wed Apr 28, 2010 3:08 am

Those prices are rediculous. You can find a regular solonoid valve for 10-30 dollars at the hardware store.

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soakernerd
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Re: need advice for making a very custom water gun

Post by soakernerd » Wed Apr 28, 2010 3:14 am

I am getting confused. Do you need the specialized valve for this, or something else? The trigger commonly used on homemade water guns is a ball valve.
for fast acting valves, a mauler valve or solenoid is best.
If I may ask, what is this other project? could you post a new thread about it to avoid confusion?

neogeo
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Re: need advice for making a very custom water gun

Post by neogeo » Wed Apr 28, 2010 4:38 am

soakernerd wrote:I am getting confused. Do you need the specialized valve for this, or something else? The trigger commonly used on homemade water guns is a ball valve.
for fast acting valves, a mauler valve or solenoid is best.
If I may ask, what is this other project? could you post a new thread about it to avoid confusion?


Yeah, sorry, I'm kind of mixing the two requests together. Let me try to pull them apart.

For the unrelated project question, I'm essentially looking for an air flow regulator that can be fully adjusted from open to closed by a servo for a line that's 1/2" OD. Why a servo? Because I'm controlling it with a microcontroller and a servo is the only option I've really got that will allow the microcontroller to fine tune its position. Most servos only turn about 180 degrees, so I would preffer to have a valve that can go from fully closed to fully open with half a turn or less. There are some servos that can turn 360 degrees, but I don't have any of those and would need to purchase one and play around with it to determine if it would also work. I would post a new thread for this question, but it would only be about this valve I need, and since it's not related to water guns in any way, I'm not sure if it's in the spirit of the website.

As for the main topic of this thread, I've currently got two things I need to work out. The first, most important one, is how to best go about pressurising my water tank to ensure that it's done safely, automatically, and reliably via either an air compressor or a fluid pump. The second problem is how to best go about triggering the flow of water out of the nozzle once the appropriate pressure is achieved. So far, the solenoid valve seems like a perfect match, assuming I can find some for far, far cheaper than what has been listed already.

Does that help sort things out a bit?

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soakernerd
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Re: need advice for making a very custom water gun

Post by soakernerd » Wed Apr 28, 2010 1:29 pm

Here is a good ball valve. It is part #4379K69. it is also relatively cheap (10$), and it rotates 90 degrees from open to closed.

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cantab
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Re: need advice for making a very custom water gun

Post by cantab » Wed Apr 28, 2010 7:12 pm

A ball valve should be turnable by a servo - but it will need to be a quite powerful servo, valves are stiff! Many people attach torque arms to them on larger water blasters. I believe brass valves are less stiff than PVC ones.
I work on Windows. My toolbox is Linux.
Arsenal:
Super Soaker: XP215, 2xXP220, Liquidator, Aquashock Secret Strike M(odded), Arctic Blast M, CPS1200, CPS2100, SC Power Pak, 3l aquapack, 1.5l aquapack
Water Warriors: Jet, Sting Ray M, Shark, Argon M, Tiger Shark, PulseMaster
Others: Waterbolt, The Blaster, Storm 500, Shield Blaster 2000, generic PR gun, generic backpack piston pumper (broken), 3l garden sprayer M, 10l water carrier:

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