Next generation rubber CPS homemade water gun planning

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Next generation rubber CPS homemade water gun planning

Postby SSCBen » Mon Jun 13, 2016 10:18 am

I started designing a new CPH based around known working technologies after Soakermore 2016. The basic plan is to make a powerful (at least CPS 2000 range), reasonably cheap, compact (XP 150 sized), light, reliable, durable, and easily repaired CPH with a ball valve trigger and backpack. You can get some pretty nice 3 liter hydration packs on Amazon for reasonably cheap ($15), so the backpack is done.

I've bounced around a lot of ideas in my head for this, but ultimately I've decided to put the project on hold until December or later. I don't have the time or focus to do justice to this project, and I want to learn a few more things. The point of this thread is mostly to collect my thoughts so I can pick up where I left off later. If you have any ideas or comments, you can make them here too.

I'm not using PVC pipe to reduce cost and also weight, and how to mount everything is not exactly clear. Rigid polycarbonate tubing is somewhat expensive. You can get clear tubing meant for packaging, which I might buy to take a look at. Either is much lighter. I have some polycarbonate tubing right now. I have experimented with using a "strut channel" as a backbone for this system, as it has some nice mounting options (you can attach a pump really easily), but I think this adds unnecessary weight and is somewhat expensive. Some sort of backbone is necessary to mount the ball valve, pump, and handle to the pressure chamber. Long term I might use a small U channel as a backbone, or use the pressure chamber casing as the backbone. The latter option should reduce weight the most, but it needs to be done in a way that won't poke the latex tubing.

The design I've been working on is somewhat nonstandard in one way: The pressure chamber input is in the back. This avoids having a tee in the flow path, which actually has appreciable energy losses and turbulence generation. The front is basically just a valve and nozzle.

I've also been thinking about using pinch triggers. The pinch trigger system described in this patent actually seems pretty decent. It has a rubber on rubber seal, and if you replace the latex tubing after a while (as you should) then I think you avoid most of the problems with pinch triggers. Pinch triggers offer a very smooth flow path and relatively easy triggers. Definitely worth looking into. But the first design will have a ball valve, as the goal is to make something reliable.

In the short term (before I go back to Texas), I'm going to conduct two relatively simple tests:

1. Latex tubing pressure tests. I'm particularly interested in how quickly the pressure decreases with use, and whether restricting the diameter of the tube helps prevent the tube from aging. Also interested in how much pressure you can get with layered tubes.

2. The effect of intermediate flow restrictions. Basically, is it okay to have the flow restrict to an area comparable to the size of the stream as long as the remainder of the flow path is large? I am going to test two different tubing barb sizes to do this. This has relevance to latex tubing blasters as it's hard to get the tubing over a large barb. If it turns out that the size of the barb doesn't matter much, then I don't see a point in trying to use a really large barb. I've avoided using latex tubing as a pressure chamber because of this, but I really only assumed the tubing barbs were bad.

Edit (New test idea): 3. Epoxy putty on polycarbonate tubing. If this works well then I might use the polycarbonate tube as the structural element.

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Re: Next generation rubber CPS homemade water gun planning

Postby DX » Mon Jun 13, 2016 1:26 pm

I'll be watching this project with a lot of interest - next gen homemade designs are very exciting and overdue.

What about constructing a shell/support material out of poly cutting board? Nerf homemade builders often use this in place of polycarb plate, as cutting board is cheaper and more durable (designed to be hacked at with kitchen knives and all). There is a version from Walmart that is softer and thicker than usual, my personal favorite, but not every Walmart carries it. Admittedly, cutting, gluing, and sanding pieces would take time and effort vs fitting the internals into tubes, but it could potentially have more of the aesthetics of a manufactured shell. 3D printing, as much as I distrust it, could also work for some shell parts. It wouldn't be under stress, tension, or pressure, just physical contact. Don't drop the soaker!

Do you know of any similar-sized alternatives to McMaster check valves? Their small size is very appealing and their high price isn't.

Pump issues from the past should be solvable today. The design I want to try involves having a main rod, with a smaller OD rod screwed into one end, with a section of main rod screwed into the other side of the smaller rod. It'll resemble a Rainbow plunger rod catch area. The seal (probably O-rings) sits on the smaller OD rod, eliminating the need to cut grooves. The main rod and its other section hold the rings in place. The screws are flat head and countersunk, so they do not stick out above the rod surface. The pump shaft is a tube with a consistent ID, like aluminum or galv steel. There are maintenance advantages to this system, simply unscrew the end to replace the O-rings. The screws can be replaced if they start to rust. There may be a better way to connect the rods, if they are metal, you'll need drill bits designed for that and patience. I've thought about materials that telescope, like brass, but I don't know where to find solid rod versions of them.

I'd also want to adapt the homemade design for onboard reservoir use. I've just never been a fan of backpacks, initially due to weight, now for the ability of air to get caught in the tubing that is frustratingly difficult to get out. They still reduce my mobility, too - anything carried on my back does, even if it's relatively weightless. The challenge of an onboard reservoir system is finding a material that is light, but strong, wide without being too wide, and has top input with side output. The PVC I traditionally use can be shaped optimally with excellent water weight distribution and screw-off fill caps, but is heavy and doesn't hold much water. Gallon jugs and the such aren't durable enough and don't have the right I/O, leading to stupid tower designs.
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Re: Next generation rubber CPS homemade water gun planning

Postby SSCBen » Mon Jun 13, 2016 3:29 pm

Glad to hear of your interest, Duxburian.

Duxburian wrote:What about constructing a shell/support material out of poly cutting board?


I have a 1" width square polyethylene rod that I intended to use for a Nerf project a while back. This could work. The main issue I see is that I'd want the support material to be reasonably light (solid 1" rod is not) and I'd like for it to be mounted flush with the surface of the tube if possible. Flush mounting would require carving out the rod. I think using an aluminum U channel with the hole being used to mount the channel flush with the PC casing might be ideal for this approach. Right now the channel I have (3230T36 on McMaster-Carr) would be facing the other direction.

On this note, I'm not planning anything with a shell. I think emulating manufactured water guns is the wrong thing to do for a few reasons. If we had the ability to exactly reproduce their designs, that would be ideal, because we could start improving on them. But we can't do that, and what we can do that's similar is not good. The shell on the Cloudburst and Riptide blasters my brother made seems more than a little impractical. The shell is heavy and has pointy edges. Not to mention that it's quite a bit of work to make.

In my approach, you mount everything you want to some sort of rigid object that is the backbone. I plan on making some sort of reasonably attractive wooden clamp of sorts to hold the ball valve and firing things firmly in place. I think it would be better to make a similar wooden clamp type thing for the pump than to use the pipe mount I have for the strut channel I bought (3193T12 on McMaster-Carr).

Duxburian wrote:Do you know of any similar-sized alternatives to McMaster check valves? Their small size is very appealing and their high price isn't.


I assume you mean tubing check valves like 2987K47 ($4.04 each). That's what I ordered. I don't think you can get anything cheaper from McMaster-Carr, but other places might have cheaper options. Building your own is an option. And buying from a manufacturer in bulk might be the cheapest per check valve, but I don't know what the total costs would be.

I forgot to describe my planned setup on this. To keep costs down, and to allow for the back filling, I'm using flexible tubing for the entire pump system aside from the pump shaft. I'll have some slack in the tubing leading to the bladder, so that when the bladder expands, the tubing moves back. This would allow the backfill.

Duxburian wrote:Pump issues from the past should be solvable today.


You're right. I've been screwing around with my brother's pump design and think it's really solid. It seals surprisingly well. I would change it to help the pump rod stay aligned a bit better at the end of the stroke, but otherwise I'd leave it as-is.

Duxburian wrote:I'd also want to adapt the homemade design for onboard reservoir use. I've just never been a fan of backpacks, initially due to weight, now for the ability of air to get caught in the tubing that is frustratingly difficult to get out. They still reduce my mobility, too - anything carried on my back does, even if it's relatively weightless. The challenge of an onboard reservoir system is finding a material that is light, but strong, wide without being too wide, and has top input with side output. The PVC I traditionally use can be shaped optimally with excellent water weight distribution and screw-off fill caps, but is heavy and doesn't hold much water. Gallon jugs and the such aren't durable enough and don't have the right I/O, leading to stupid tower designs.


On-board reservoirs are pretty difficult and I want to avoid these problems entirely for the time being. I can very easily get caught up in problems like this, thinking about what the best way to do things would be rather than doing something. I'm very satisfied with the hydration pack I bought aside from the capacity, and to be honest, 3 liters is pretty good for most blasters anyway.

I'll think more about this, though, as I recognize this is something many people want. (I recall my survey showed there was a lot of interest.)

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Re: Next generation rubber CPS homemade water gun planning

Postby SEAL » Mon Jun 20, 2016 11:44 am

Yes, I've been wanting to see improved homemade designs for a long time. We need to reach a point where homemades are competitive with stock CPS soakers for a reasonable cost.

I agree that a "backbone" would probably be better than a shell. Picture like a short piece of two-by-four with everything (reservoir, pump, PC) attached to it. I also agree that PVC isn't the best option, at least for most parts. Flexible tubing like stock soakers use is lighter and more space-efficient.

I also prefer an onboard reservoir. I wonder if it's possible to 3D print a reservoir. They don't have to be as strong as the pressurized components. You could also use thin-wall PVC drainage pipe. It's much lighter and holds more water than the pressure-rated stuff. They even make unscrewable caps for it.

The pump I made in the thread you linked to actually sealed very well. The only thing was, the XXP 175 I was trying to fix is a PR gun, and for those you need to let air in on the out stroke. Doh! I made it by plugging one end of a piece of CPVC, and cutting three O-ring grooves with a lathe. I guess if you have access to a lathe, then O-rings will work. Just use more than one. I've also converted a bike pump to move water before, however you'd need the right kind.
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Re: Next generation rubber CPS homemade water gun planning

Postby marauder » Mon Jun 20, 2016 1:33 pm

SEAL wrote:The pump I made in the thread you linked to actually sealed very well. The only thing was, the XXP 175 I was trying to fix is a PR gun, and for those you need to let air in on the out stroke. Doh! I made it by plugging one end of a piece of CPVC, and cutting three O-ring grooves with a lathe. I guess if you have access to a lathe, then O-rings will work. Just use more than one. I've also converted a bike pump to move water before, however you'd need the right kind.


You're not the only one who has done something dumb like this with pumps and valves. I made a sick launcher but the valve is facing the wrong way.


I still say that ergonomics and durability are the 2 biggest factors in preventing homemades from seeing much use. If something doesn't work, you can't use it. Unfortunately, I've yet to see anyone have a real usable homemade on the battlefield.


Oh, and I was favoring backpacks with my frankenstein mods, essentially homemades into and of themselves, but when it comes to action, I found I also prefer on board reservoirs.
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Re: Next generation rubber CPS homemade water gun planning

Postby SEAL » Tue Jun 21, 2016 4:03 pm

I forgot to mention triggers. Anyone ever consider using a bicycle handbrake for a trigger? Squeeze it, and the cable pulls open the firing valve. Handbrakes spring back when you let go of them; not sure if they would do the same thing when connected to a valve, but if they did, it would be great because you wouldn't need to fashion a return spring for the valve.
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Re: Next generation rubber CPS homemade water gun planning

Postby Drenchenator » Wed Jun 22, 2016 8:09 am

I've considered bicycle handbrakes for triggers when I was coming up with ideas for Riptide. The only problem that I saw at the time was the the trigger pull length would be very low and only suitable for pull valves. I wanted to use a ball valve, which needs a lot of pull length, so I used a rotary trigger.

I think there are a lot of good ideas in this thread. Ben's criticism of my Riptide and Cloudburst designs is completely correct: the shells were heavy and bulky (especially on Riptide), and you can only go so far "emulating" the classic CPS designs, which was my goal. There are two "innovations" that I think I got right though:

1) Pump design. The rubber grommets work very well and I have never had any seal issues. They are also easy to maintain (just swap them out!). The only restriction I would say is that I've had issues with wooden pump rods fracturing after a while (likely due to the screw), so I'd recommended plastic pump rods for a more permanent solution.

2) Trigger design. The Riptide trigger design, in retrospect, is rock solid. Riptide is the only one of my homemades that still works largely, though it is very heavy (9 lbs when loaded, if I remember correctly). The trigger design suffers from obviously being left handed, so in Cloudburst I tried to switch to something else that did not work at all. But the Riptide trigger design is great for ball valves, because it uses the "lever effect" to create a high amount of force to open the valve and it gets more than enough distance to open it fully. In retrospect, I should have tried to improve on this design for Cloudburst rather than strap it.

Largely I think the shell idea in Riptide was interesting but a failure. It's just too heavy and bulky! The shell on a stock blaster is thin and sculpts around the parts, while my shells were too rectangular, too full of air, and too thick. I also tried to use too many PVC parts, which are also too bulky and heavy. Hence, the designs were too bulky and heavy. If we could move to lighter and more agile designs, it would really put homemades in the same class as stock blasters.
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Re: Next generation rubber CPS homemade water gun planning

Postby Tim » Wed Jun 22, 2016 4:08 pm

Ben–

Come on, Ben! Give the people what they want: an onboard reservoir! In all seriousness, you should build what you prefer. There will be enough complications trying to improve the core CPH design. A reservoir would be great to consider for a subsequent version. I want my next build to have an onboard reservoir simply because I just finished making a soaker with a backpack reservoir.

FlexPVC.com is a good source for 3” & 4” acrylic tube. They’ll cut it to the exact length you need in inches.

I really like the backbone idea. The low-profile aluminum strut channel that you already have is probably best suited for this. Using the pressure chamber case as a backbone is a good idea, too. You would have to countersink the small screws/bolts from the inside. A right-angle attachment on a rotary tool would be good for this. It might be a good idea to put some silicone sealant over the countersunk screws to eliminate sharp edges.

Having two connections for the LRT could be brilliant. For the pump connection, perhaps you could use self-retracting tubing like McMaster part number 9148T115 or 9148T165 inside the PC case.

Drench–

Agreed; the Riptide trigger and pump are fantastic.

If someone did attempt to use a bicycle handbrake for a trigger, perhaps they could use a Travel Agent to nearly double the cable pull length and actuate a ball valve. Yes; you’d lose some mechanical advantage, but a handbrake lever should have mechanical advantage to spare in our application.

VR,

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Re: Next generation rubber CPS homemade water gun planning

Postby Drenchenator » Wed Jun 22, 2016 8:10 pm

Like Ben, I actually prefer not to have an on-board reservoir.

A reservoir takes up a lot of space. If you are using cylindrical CPS to power the gun, the logical place to put the reservoir is behind the chamber, which makes the gun even longer. 4 inch PVC drain pipe is the cheapest and most readily available material for reservoirs, but it actually isn't wide enough for sufficient water storage. To get a 3L capacity, a reservoir made of 4 inch drain pipe would need to be 15 inches long, and 4L needs 20 inches.

So the reservoir issue really is about what materials are available. Measure a CPS 2000's reservoir, and you will see that it is very wide --- a large bulb at the end of the gun. This is how a reservoir should be made, but unfortunately materials to pull this off do not appear to be readily available. 3D printing comes to mind, but given the large size --- perhaps greater than 6 inches in each direction --- home 3D printers made not be capable of this (right now at least, though please comment if I'm wrong).

Does anyone have any other ideas for materials for a reservoir? A small gas can could work, but usually those are at least 2 gallons (~8 L) and may be too heavy for normal use.

Still, it seems that most people want it, so I did have some ideas about it. For Cloudburst I designed the pressure chamber attachment points to act as a "utility rail" of sorts so that you could support an on-board reservoir.

Image

This is the "utility rail" region of the gun. The pressure chamber shell locks in place at the end, and it is secured at the dowel on the left.

Image

This is the pressure chamber shell, detached from the body. Instead of the standard pressure chamber shell, which runs the length of the body, I had an idea to divide the pressure chamber shell in half and use the other half of the gun's body to support a reservoir. To get the needed capacity, the reservoir would have to run past the length of the body, but it's doable given the design.

I never got to build this idea due to Cloudburst's bad trigger basically killing the design, but I think it's a decent idea for how to properly include a reservoir as an organic part of the overall design. Granted, I never built it, but in theory it should work, but it will have the length issue I discussed earlier.
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Re: Next generation rubber CPS homemade water gun planning

Postby Tim » Thu Jun 23, 2016 7:07 am

"Does anyone have any other ideas for materials for a reservoir?" - I have several ideas, I just need to know what capacity is appropriate. You mentioned 3 liters & 4 liters. What do others think? SEAL, marauder, DX, anyone else?

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Re: Next generation rubber CPS homemade water gun planning

Postby Drenchenator » Thu Jun 23, 2016 8:04 am

Personally, I think 3L is good standard for a "high-powered" blaster. 4L is probably the max we can go without it getting too heavy. 4L is 4 kg (8.8 lbs) of water, so really is a lot of weight to carry with your arms, though I guess another variable to consider is whether or not to have a strap. Personally, I like straps but I know some people don't.

2L is probably appropriate for a mid-range blaster (around the XP 150 in size) and would be completely appropriate for a gun without a strap (in my opinion). Though the weight issue really comes down to personal preference.
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Re: Next generation rubber CPS homemade water gun planning

Postby SEAL » Thu Jun 23, 2016 11:33 am

3L is actually quite large for current soakers. I believe that's the size of the CPS 2700's reservoir, which is the biggest onboard of any stock gun. But as long as the soaker is well balanced like the 2700, the weight is no problem. I wouldn't mind going up to 4L, especially assuming we want bigger and more powerful nozzles than stock offerings.

Edit: Actually it seems the 2700 has a 4L reservoir. In that case, that size is totally reasonable, and we could perhaps go even bigger. All depends on the application though. In battles where I'm scouting and going after flags and what not, I'd prefer something smaller.

As for reservoir materials, I'll look into 3D printing. I think we have some pretty big printers on campus. That would be the best option because you could make it any shape you want to fit the blaster in question. Can't really think of much else off the top of my head at the moment. There are probably some types of containers out there that will work.
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Re: Next generation rubber CPS homemade water gun planning

Postby DX » Fri Jun 24, 2016 11:25 am

My ideal onboard reservoir size is probably around 2.5 to 3 liters. That is the range of capacity from a CPS 1200 to a 2000, and all I really need.

One option I've thought about is a portable gasoline canister. They are lightweight, but strong, wide, but stable, and come in a variety of shapes and sizes. They also often have a threaded spigot, so you could in theory attach them easily if you could find the right shape.
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Re: Next generation rubber CPS homemade water gun planning

Postby SSCBen » Sat Jun 25, 2016 6:21 pm

For you all's information, I was not able to do my planned tests, but I'll get to them later.

Tim wrote:FlexPVC.com is a good source for 3” & 4” acrylic tube. They’ll cut it to the exact length you need in inches.


Good to know that they'll cut to the inch. My experience with acrylic is that it's way too brittle to be of use to us, though. Polycarbonate is much better, though still fairly brittle when compared against non-translucent plastics.

Tim wrote:I really like the backbone idea. The low-profile aluminum strut channel that you already have is probably best suited for this. Using the pressure chamber case as a backbone is a good idea, too. You would have to countersink the small screws/bolts from the inside. A right-angle attachment on a rotary tool would be good for this. It might be a good idea to put some silicone sealant over the countersunk screws to eliminate sharp edges.


I'll keep this in mind. I don't know much about how to attach something circular to something flat.Countersinking the bolts/screws sounds like the right thing to do. I was thinking about using electrical tape to eliminate the sharp edges, but silicone sealant would probably look better if the pressure chamber case is clear.

Tim wrote:For the pump connection, perhaps you could use self-retracting tubing like McMaster part number 9148T115 or 9148T165 inside the PC case.


I thought about this too. I'm not sure how rigid the self-retracting tubing is. It might not be suitable for this purpose if it can't be cut short. I assume it's like the tubing I see used on air compressors, which seems like it would basically fracture if I tried to cut it.

SEAL wrote:As for reservoir materials, I'll look into 3D printing. I think we have some pretty big printers on campus. That would be the best option because you could make it any shape you want to fit the blaster in question.


3D printing could be okay, but I'm concerned by how much of the volume would have to be removed. Reservoirs are hollow, and it'd take a lot of support material to do this. If it's possible to periodically stop the printer to insert wood blocks or something similar to hold the other wise up, this might work.

Duxburian wrote:One option I've thought about is a portable gasoline canister. They are lightweight, but strong, wide, but stable, and come in a variety of shapes and sizes. They also often have a threaded spigot, so you could in theory attach them easily if you could find the right shape.


I think this is a good idea. I'll have to look for the ones with the spigot, as otherwise you'd have to use a through-wall fitting or something similar.

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Re: Next generation rubber CPS homemade water gun planning

Postby Tim » Sun Jun 26, 2016 8:26 pm

All,

As Ben pointed out, polycarbonate would make a better PC cover than acrylic. McMaster sells economical polycarbonate tube for flow in 3" ID (3-1/4" OD), 3-1/4" ID (3-1/2" OD), 3-3/4" ID (4" OD), and 5-3/4" ID (6" OD). They also sell less economical polycarbonate tube for fabrication in 4-1/4" ID (4-1/2" OD), 4-3/4" ID (5" OD), and 7-3/4" ID (8" OD). Which of these ID's is most suitable considering 2-3 layers of LRT plus multiple layers of innertube?

For a 3-liter reservoir, you can't beat Touratech's 3-Liter Fuel Canister (8.25"L x 4"W x 8"H).

For a ~3.8-liter reservoir, this is going to be a matter of preference (and is a bit dependent on the PC cover question above). If you are more worried about keeping the overall length & width of the soaker shorter, go with Midwest Can's Model 1200 (7.5"L x 5.25"W x 9.5"H). If over all soaker height is important to you, run with Briggs & Stratton Model 95013 (8"L x 5.9"W x 8.1"H). If style is your priority, you might consider Blitz's Model 85005 (9.5"L x 5.88"W x 8.5"H). Which of these three reservoirs do you like best?

For a 4-liter reservoir, I think the best choice is Barrier Plastics' 4-Liter Jerry Can (7.25"L x 5.5”W x 8.3”H). This container is very space-efficient because it is so cube-like. Also, I think the recessed area on the bottom will nest over strut channel, reducing the overall height.

I looked into containers with spigots, but the dimensions were not ideal. It's not difficult to install a bulkhead fitting. You can even make your own bulkhead fitting (Google it).

Ben,

The self-retracting tubing that I pointed out (McMaster 9148T115 & 9148T165) for inside the PC case is very flexible and easy to cut. It is made of the same polyurethane (Shore A95) tubing that I used on POPCAP, except its memory is for the coiled shape instead of straight. This is nothing like the junk nylon tubing commonly used with compressors.

VR,

Tim

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Re: Next generation rubber CPS homemade water gun planning

Postby Tim » Wed Jul 06, 2016 10:37 pm

<bump>

I think Ben is really on to something here. I was hoping there would be more interest in this thread. No worries, I will design what I think is best, and I can tweak the final design before building in January.

I will go with the 4-1/4" ID (4-1/2" OD) polycarbonate PC cover. This will allow me to use these shallow, flat PVC end caps. I need a lightweight (but sturdy) end cap to mount the firing valve and associated hardware. For serviceability, none of these internals will mount to the PC cover. I will mount the PC cover to the strut with hardware commonly used to mount flat signs to large-diameter poles.

I am going to pursue SEAL's idea of using a bike brake lever. A typical mountain bike v-brake lever has about 30 mm of cable travel. If I need more than that, I can use the "Travel Agent" I mentioned. This will also facilitate a 90-degree turn with the brake cable before it attaches to the valve with a go kart throttle clevis.

I'll use a compact 3/4" PVC ball valve because the actuation force required for a plastic valve is far less than for a metal valve. That is why small plastic valves can have such tiny handles.

To spring the valve closed, I'll use a constant-force spring (like in a tape measure, but stronger). This takes up less space than a regular spring and has the same recoil force regardless of how much it is retracted.

I will use regular-height fiberglass strut channel instead of the aforementioned half-height aluminum so the pump can be fully contained within the strut. I will slot the strut with a Black & Decker RTX so the pump is tracked. The pump handle will be a square sleeve around the strut channel with tennis overgrip around it.

I am designing with the 4-liter container I identified in my previous post. I will attach the tank with bolts, fender washers, and rubber washers. I have done this successfully on other types of projects with no leaks. If I use a rear end cap, I can throw a bulkhead bolt through there, too.

Image

I will run with Ben's proposed rear LRT connection for pumping. How much should I expect the LRT to grow in length? 2:1? Should I put bike tire tubes over the LRT? How many layers of tire tube?

VR,

Tim
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Re: Next generation rubber CPS homemade water gun planning

Postby SSCBen » Thu Jul 07, 2016 11:50 am

Nice ideas. Not much time, but I'll make some quick comments.

I think a 4.25 inch ID tube is way too big. The standard latex tube I use expands to about 3 inches in diameter if unrestricted (and about 3 times in length; see the LRT article for details). I think there is also good reason to restrict the tube diameter. Doing so should increase the life of the tube as it would experience less strain per cycle. I don't recall the exact size, but the polycarbonate tube I bought had a 1/16" thickness and OD of about 2.5 inches. Not sure if this is too small to be useful; I intended to do tests.

Good idea to track the pump with the channel. I had the same idea after I got my channel and realized 1/2 inch PVC would fit. There are a number of accessories that should help with this, but I think you already have it figured out.

I am skeptical of your ball valve setup. My experience suggests that PVC valves are harder to turn, and larger valves are harder to turn. You might want to experiment on this. I have been thinking about making a 3D printed pinch valve lately, so you might want to consider that too. Pinching latex tubing would have some advantages. Better seal and the tube would be periodically replaced, avoiding the valve sticking open, etc.

As for how much to layer, the SuperCPS design might offer a good starting point: http://www.sscentral.org/homemade/supercps.html

More coming this weekend.

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Re: Next generation rubber CPS homemade water gun planning

Postby Tim » Thu Jul 07, 2016 7:25 pm

Hey Ben,

"I think a 4.25 inch ID tube is way too big." - The large OD allows me to put the valve inside the PC cover. Maybe I'll just build up the bladder to a larger OD. I'm thinking I might try to use Gum Rubber Tubing (GRT) instead of LRT. Sling shot enthusiasts use LRT and GRT interchangeably. They admit the LRT has a little better performance initially, but the GRT has much greater durability and longevity. I can get the bladder to a 2.75" OD with just three layers of GRT. Maybe a smaller OD than this would be okay because GRT is more durable.

"Good idea to track the pump...I think you already have it figured out." - Actually, I don't already have it figured out. I have not started modeling that part of the blaster yet. I would greatly appreciate any ideas you can throw my way.

"My experience suggests that PVC valves are harder to turn..." - Are you referring to the white full-port PVC valves commonly found at Home Depot? In my model, I have a Specialty Manufacturing reduced-port valve (5/8" ID like on POPCAP). Look at how tiny the plastic handle is; this would not be adequate to turn a 3/4" metal valve.

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"I have been thinking about making a 3D printed pinch valve..." - Sounds like a great idea. Put it up for sale on Shapeways and I'll buy one.

I was able to update my model a bit this evening...

Image

VR,

Tim

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Re: Next generation rubber CPS homemade water gun planning

Postby Drenchenator » Thu Jul 07, 2016 10:31 pm

Tim, I love your planned layout. Everything fits neatly on a single rail, so there's no need for "internals." The bike handle as a pistol grip is a pretty interesting idea, though personally I prefer a real pistol grip (since they are available). It's personal choice, though, and certainly a bike handle is much better than a PVC pipe!

Your pump ideas are pretty original, so I look forward to seeing how that plays out. Moreover, the design seems to have a much lighter feel than any of mine, which all look pretty bulky in retrospect. The 4L reservoir definitely looks the part and pretty much hits my design target, at least. How long is the blaster and how much will it weight empty and full?

Like Ben, I too am rather skeptical about the choice of a plastic ball valve, though I'm really only acquainted with ones at Lowes and Home Depot. The trigger system is pretty novel and represents a big leap forward should it work. Most homemade triggers systems are failures (only 1 of my 2 designs worked). I don't think the issue is necessarily will the value open --- with enough force, it will --- but I think with such little travel available, even with the "Travel Agent" gadget, it may be difficult to pull to trigger. Perhaps you should test the forces created and needed beforehand to shore up the design in this aspect. This is one of the reasons I dislike the modern inclination to immediately CAD something; pen and paper still works wonders. I'm not saying it's impossible; I'm just saying that it's tricky and you'll need to plan accordingly. Best of luck, though!

Still, I love the overall design and it appears very well balanced. I look forward to your build progress!
The Drenchenator, also known as Lt. Col. Drench

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Re: Next generation rubber CPS homemade water gun planning

Postby SEAL » Fri Jul 08, 2016 2:04 pm

Wow, looks good. This type of innovation has been a long time coming.

How are you planning to do the reservoir-to-PC connection? A flexible tube that snakes along the side is probably the best option. I recommend having the tubing and pump be as wide as possible, for better flow. Pump volume is an important stat, but so many homemades seem to use puny little half-inch diameter pump shafts.

I'm looking forward to seeing how this GRT stacks up to LRT. I've always been kind of skeptical of CPHs because it seems like every single person who's built one has had the PC rupture.

My mountain bike has this fancy "short reach" brake lever. It's much easier to pull and has less travel than a regular one, but does the same amount of work. I don't know much about bikes, but that could be something worth looking into.
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