Water gun structures

[Ben]

That's a great solution! Definitely worth trying. If we have something the same size as the opening leading back, there wouldn't be a problem at all. The problem would be getting something larger to seal, but that wouldn't be much of a problem with the repair couplings.

For those who don't know what a repair coupling is, here's a picture of a 1 inch one:



Basically it's a telescoping piece of PVC pipe. It can telescope because it has O-rings inside of it. They're a little expensive in large diameters, but they can be very useful. They can be the seal between the pin and the valve casing.

[wetmonkey442]

These are great ideas being thrown around, and it will definitely be interesting to see how they manifest themselves in coming designs.

Another simple solution to improve ergonomics and overall look would be to cut down on dead space by restructuring the overall organization of the PVC. In the past many designs have been bulky and unwieldy and while certain designs (like the APH) require a certain look, I think that with CPS homemades we might be able to improve overall look. I recently sketched a design which utilized some of these concepts, and I'll edit this post later with a picture.



It's pretty easy to discern the design from this picture. A few obvious flaws include the large amount of dead space between the two check valves. However, it provides for a cleaner look, and a more comfortable way to hold the gun, with the bulk of the weight behind the handle (the connecting tees between the pump and the nozzle). The reservoir would be a 2 liter bottle, situated either straight down, or one side running parallel to the body.

[Ben]

Reducing dead space was a goal with my THR water gun, and a structure to mount on helps it. Everything was linked together with tubing for the most part. The reservoir-pump connection and pump-PC connection are both done with tubing. That alone adds a lot of flexibility in part placement, which reduces dead space. Of course, now I'm thinking of ways to reduce dead space further. The two holes in my plexiglass could be closer, but I don't plan on using something exactly like that again for ease of building.

I'm looking forward to see your picture too. Any new ideas are helpful. We've discussed a lot of great ideas so far.

[Silence]

Unfortunately, rubber tubing expands in all directions, including lengthwise. One end has to be able to move freely, either by not having any connections on it or by allowing it to slide along a long tube. Generally, both the inlet and the outlet are connected to the same side, as with a spherical bladder.

That's certainly a nice design though. Even if you had the inlet going through the front, then the balance still wouldn't be too bad since the bladder will expand to the rear when filled.

[wetmonkey442]

I understand that tubing expands lengthwise, and that by inhibiting lateral movement I would be drastically decreasing the power of the water gun. However, I don't think that it would completely negate the usefulness of the design. Am I completely wrong in assuming that such a design (wherein only one direction of expansion is allowed) would still perform adequately. Understand that with this design I am not aiming for optimal performance, but increased usability.

As you suggested a modification to allow for flow in and out of the same orifice might be the solution, but I'm worried about how that would affect the overall design.

[Silence]

From what Ben's explained in the past, it seems that it's pretty much impossible to get the tubing to not expand lengthwise. It will probably try to bend and contort, which would make it burst. And even that's with a frame that resists lengthening or breaking.

Speaking of which, what holds the two halves of your design together? They appear to be connected by two flexible tubes.

I honestly do like the design, but you may want to glance at how CPS water guns and homemades use bladders. You may be able to get ideas from the SuperCPS and the Tactical High Range water guns.

[Ben]

I agree with SilentGuy. There's no real benefit in using both sides. I've seen a variety of interesting designs that uses that side, but half of them are bad because they don't allow for expansion in length. My first CPS gun design used both ends of the tubing, but I quickly saw why that should be avoided. Using a tube leading to the end would solve the expansion, but there's no reason benefit to using both sides. I can't think of a good reason to do that other than to be different than the norm.

You're not wrong that it won't perform bad if you can't get expansion lengthwise, but it will definitely try to expand. I don't know if you've messed around with LRT, but had I made the design I planned originally, the gun would have started bending in one part as the LRT expanded. The LRT might burst if it can't expand. The LRT definitely wants to expand and it will expand. So solid designs holding the tube in place are out of the question. Something flexible with tubing could work, but again, I see no benefit over a standard design. If it works for you, that's great. But I don't see it as any better than a standard design. There's a reason Larami used only one end of the PC.

As far as dead space is concerned, my SuperCPS gun and the newer THR one don't have much to begin with. The THR does have some, but it could be eliminated easily by positioning the parts closer to each other. Check it out if you haven't already: http://forums.sscentral.org/t4728/

This might seem a little weird because SilentGuy beat me to the post and I'm reiterating much of what he said.

Edit: I'm going to draw up the basics of my current THR2 idea. I'd like to get some evaluations/suggestions of it.

Edit again: I read this again and I seemed a little harsh on the idea to use a tube leading up to one end of the bladder. Let me say what I meant more clear; both are fine designs.

[Drenchenator]

I honestly do like the design, but you may want to glance at how CPS water guns and homemades use bladders. You may be able to get ideas from the SuperCPS and the Tactical High Range water guns.

Yes, I have to agree. The design is sound and should work; but I think Larami did separate chamber CPS right the first time with the CPS 2000--there's really no reason to completely redo what has already worked. The tried-and-true system can waste a lot of space, but it also save a lot of space by keeping the design simple. Using smaller check valves can help: Notice that all stock CPS guns fit both check valves at the end of the pump shaft. And in most CPS guns, the space is used incredibly efficiently, because all of the parts are close together and small. Dead space isn't there because the parts are smaller and made to fit together.

[wetmonkey442]

Ah, I understand. Well, as everyone has pointed out, the design can be easily modified to allow for both the inlet and outlet to be attached to the same opening.

Originally Posted by SilentGuy

Speaking of which, what holds the two halves of your design together? They appear to be connected by two flexible tubes.

Using some sort of plastic sheath to protect the bladder could serve as both a means of guiding the bladder back as it expands and also connecting the two halves firmly.

[Drenchenator]

Using some sort of plastic sheath to protect the bladder could serve as both a means of guiding the bladder back as it expands and also connecting the two halves firmly.

It would be a good idea to also include a disk at the end of the bladder so that the "butt" of the gun does twist and rotate, keeping it fairly stable. Just a though.

[Ben]

THR2 is about done in my mind. There are a few things I'll decide when I get the parts in front of me, but I have the basics done. I've made a few drawings of THR2, but they'll be a little hard to follow without explanation. I think this is where CAD comes in, but I don't have a CAD program at the moment. I'm looking into installing AutoCAD sometime this week.

The gun itself is a similar layout to the first THR, but it has a different structure, triggered valve of some kind, and a nozzle selector. With the different structure, I'm looking to tighten up the design so it is less tall and has less dead space. The structure itself is going to be mainly two pieces of plexiglass that sandwich the two main pipes between them. That structure is actually easier to make than the sliding pieces I used before because you don't need to use a router with precise measurements. So THR2 should be a complete improvement upon THR.

I'd also like to use some lighter and cheaper components, like the ~$3.50 polypropylene check valves McMaster-Carr offers that are small and can fit into tight spaces. The new THR2 design also allows me to use thinner, lighter, and cheaper plexiglass. I might use another plastic though, depending on how I want the gun to look and what's available for cheap. To save money, I plan to buy scrap from a plastic shop.

The design in my head isn't final because I want to finish up THR and test it out. I might not finish up THR for a while due to bad weather and college, but right now I have at least 80% of the work done, so I have a pretty good idea how it has worked. I'd like to give it a battle test though.

[Ben]

After some thinking, I'm going to make a CAD drawing of THR2 rather than a hand drawing. When you get seriously 3D with layers, it's hard to draw it, especially if you are bad at drawing. For me to draw it acceptable would probably be more work than making a CAD drawing. I'm going to install AutoCAD tomorrow and try to learn a thing or two.

While I've used CAD before, I've never used it for a water gun project. Previously my water guns were relatively simple in design and didn't require much thought before, but now that we're approaching more manufactured-like water guns, more thought is required.

I also had been doing some math concerning triggered ball valves. If we lubricate the ball valve, I think we can get one that works will with a trigger pull of less than one inch to about 1.5 inches. Brass ball valves are necessary because they have much less friction. I don't know how much torque is necessary, but I'd be fine with a moderately hard trigger pull. I don't imagine the trigger pull will be moderately hard, but if it is, that's okay.

After doing some research, you want a lubricant that won't harm the seals in the valve. Here's on that apparently is perfect: http://www.plumbingsupply.com/lube.html

Calculating trigger pull is relatively easy. All you have to do is take 1/4 of the circumference of the circle that the ball valve's torque arm will travel. With a 1 inch torque arm that means a 1.57 inch trigger pull. A 3/4 inch torque arm is a 1.18 inch trigger pull. A half inch torque arm is an 0.79 inch trigger pull. I think it will take some experimentation to get the trigger right. For comparison, Drenchenator used a 1/2 inch torque arm (0.79 inch trigger pull) and older Super Soakers have about an inch trigger pull.

With THR2, the first thing I'm going to try will be a triggered ball valve because I don't want to mess with seals. If that doesn't work, I would like to figure out how to use rapid prototyping equipment to make a quality pull valve. I realize most people wouldn't have access to such equipment, but now that I'm at college, I do, so I'd like to see what I can do.

I might edit in more later.

[Silence]

Do brass ball valves really have less friction, or just more torque under normal circumstances due to the built-in lever, as you suggested before?

Just get generic silicone lubricant for the seals. It's proven not to affect plastic or synthetics, unless you slather so much that it congeals. I'm positive that's what the "Super Lube" in the link contains.

It's nice to see more complicated designs, especially when you're actively seeking to refine the process. I don't think AutoCAD's the best tool to learn with - it's actually quite complex - but you'll probably use it later for something not related to water guns.

Also, don't worry about whether or not readers have access to CNC machines - there are online services that make rapid prototypes much more accessible. Just make sure to link to one if you write an article for THR2.

I can't wait to see the water gun...

[Drenchenator]

Do brass ball valves really have less friction, or just more torque under normal circumstances due to the built-in lever, as you suggested before?

I really don't know that answer to that. Either way, brass ball valves would be the ones a builder should use for a trigger water gun because they are smaller and can have custom arms (though they are much heavier). Ben and I don't have a force meter, so we can't find out for sure the forces/torques involved. It would certainly be interesting to try out. Maybe in the future.

As for Ben's THR2 gun, I've seen his basic hand drawing of the gun: It sorta combines his THR and my first homemade; it's a bit hard to describe but I guess I'll see the final product before anyone else. I'm not complaining.

[Ben]

Do brass ball valves really have less friction, or just more torque under normal circumstances due to the built-in lever, as you suggested before?

After messing with a brass ball valve and a PVC one, I think the brass valves are easier to turn than the PVC ones. I was wrong before about it just being the torque arm, but I do think the torque arm helps a lot. Turning while holding the torque arm at a point about as low as on the ball valve still is easier to turn. But there's another reason to use them as Drenchenator mentioned. Plastic ones don't have removable torque arms, so brass valves are easier to modify.

Though, it depends on several factors. I've noticed that the ones with the red handles are harder to turn than the ones with the black handles. I don't know which company manufactures which, but that rule has held true for all the ball valves I've used. The black ones are closer to as easy to turn as brass valves, but not quite there. The valves seem easier to turn after some use too.

Just get generic silicone lubricant for the seals. It's proven not to affect plastic or synthetics, unless you slather so much that it congeals. I'm positive that's what the "Super Lube" in the link contains.

I'm just going by what this page said: http://www.plumbingsupply.com/pvcvalve.html

Possibly the problems don't hold true for brass valves, but it's not like the product they recommended is expensive, so I think I'll go with the SuperLube. I'm still doing research though, so I might go with something else.

I don't think AutoCAD's the best tool to learn with - it's actually quite complex - but you'll probably use it later for something not related to water guns.

The main reason I want to use AutoCAD is because I have a copy of it and some experience with it. In my introductory engineering class, we used ProEngineer, which is pretty nice too. Someone I know copied the entire student edition of the program into a portable hard drive and used it on their computer, so I might do that if I don't like AutoCAD. I figure it's valuable to be familiar with more than one program.

Also, don't worry about whether or not readers have access to CNC machines - there are online services that make rapid prototypes much more accessible. Just make sure to link to one if you write an article for THR2.

I didn't know they had online services for rapid prototyping. I thought you had to generally pay a company to make the prototype, but I'll admit I know little about the subject, just that they have several CNC machines at the University of Maryland.

As for Ben's THR2 gun, I've seen his basic hand drawing of the gun: It sorta combines his THR and my first homemade; it's a bit hard to describe but I guess I'll see the final product before anyone else. I'm not complaining.

That's one way to put it. It's like both because it positions the parts similarly to THR with a case.