Arm Mount - First Homemade

Build a homemade water gun or water balloon launcher and tell us about it.
AquaLepus
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Arm Mount - First Homemade

Post by AquaLepus » Fri Jul 25, 2008 3:14 am

Hello all,

I'm new here, because my friend and I wanted to make our own [better] water guns for this annual marching band water fight. I decided to try a model that mounted to your arm. It's basically like the SuperCPS but with some turns and the ability to be operated with a single arm.

I'm almost done with my parts list, but I've run into an issue:

The LRT chamber is mounted on the bicep, so there has to be a flexible part to cross the elbow. Problem is, I don't know if I should use another length of LRT or some vinyl tubing. I'm trying to find the most space-efficient method so that I don't sacrifice LRT length or comfort (i.e. having a PVC pipe extend above my head).

Thanks,
AquaLepus

aEx155
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Re: Arm Mount - First Homemade

Post by aEx155 » Fri Jul 25, 2008 3:27 am

Welcom to the forums, AquaLepus!
AquaLepus wrote:Hello all,

I'm new here, because my friend and I wanted to make our own [better] water guns for this annual marching band water fight. I decided to try a model that mounted to your arm. It's basically like the SuperCPS but with some turns and the ability to be operated with a single arm.

I'm almost done with my parts list, but I've run into an issue:

The LRT chamber is mounted on the bicep, so there has to be a flexible part to cross the elbow. Problem is, I don't know if I should use another length of LRT or some vinyl tubing. I'm trying to find the most space-efficient method so that I don't sacrifice LRT length or comfort (i.e. having a PVC pipe extend above my head).

Thanks,
AquaLepus
Well, from what I can tell, your problem is the bending area between your forearm and bicep in the LRT case could cause problems, right?

I really don't suggest allowing the LRT to bend, espcially if it's going to be a dynamic (moving) bend, rather than static. Bending the LRT while it's filled could cause rupture, so it would be best if you could make the LRT casing straight. If you really want it to be "arm mounted", you could mount the LRT + LRT case on your back, and have the pump and nozzle/trigger assembly (connected by hoses) on your arm; that way, you can have the LRT expand without bending but still have it on your arm.

Another method, although not the best, would be to have two lengths of LRT mounted seperatly to your forearm and bicep. You would connect the bicep portion with some tubing to the inlet (not the back of the other portion of the LRT since it needs to expand) so you can have the LRT case split.

I really don't see any benefit of having an "arm mounted" gun. It seems like it would be a bit awkward to hold compared to having it on a shoulder strap. Either way, you could try those idea or just make it regularly.

I'll see if I can make a diagram, but I can't now. If my ideas seem a bit complex, then I'll explain the hard parts in detail if you need me to. (not to say you can't understand it; it's just that I'm always confusing... :rolleyes: )

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Silence
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Re: Arm Mount - First Homemade

Post by Silence » Fri Jul 25, 2008 3:28 am

Welcome aboard! Too bad my band doesn't have water gun fights. :)

Note that latex rubber tubing can't bend (without bursting) when it's full. Also, it increases to 3 times it original length, so a bladder around your elbow may not work.

Your water gun sounds similar to the A.R.M. 4000 XL (sorry for no links - there's not much information available out there). It had a pump from the wrist to the shoulder so it could be pumped by one bicep, and a small pressure chamber on the side of the bicep or something. A novelty, if you will.

Honestly, I wouldn't suggest doing much beyond SuperCPS if you want constant performance. The APH has an even more complete walkthrough, and it gets good performance. I promise there will be lots of minor things that come up and could delay your build, especially if this is your first homemade water gun.

Anyway, good luck! Hopefully somebody else will have a link to the A.R.M. 4000 Xl.

AquaLepus
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Re: Arm Mount - First Homemade

Post by AquaLepus » Fri Jul 25, 2008 3:58 am

Thanks for the quick replies,

I might have been unclear in my description. The main LRT chamber will be stationary on the bicep, so it's not the thing bending. The barrel part of the gun will be secured to the forearm. So the connection between the main LRT chamber and the forearm barrel needs to bend in some way. If I have time tomorrow I'll get a concept sketch up here.

Although, having the LRT chamber on my back would take a fair deal of weight off my arm and increase mobility. Though, I was planning to have the water stored in a backpack, so I'd have to rig the two together or something.

Of course, another issue is that when my arm is bent or straight, the flexible tubing's length will change. I'm wondering if there's any handy material similar to those bendy-straws? Where the actual length of the tube can increase and then decrease. (I realize that this material would not be ideal for laminar flow, however) Though, when firing, my arm would be completely straight.

The pump would technically be the same as any old water gun - the "one hand" bit will only come in if I can design a decent pump handle of sorts. It's an area I haven't thought out very far because I could always use a normal pump. Plus, since I haven't worked a whole lot with PVC, I might abandon the arm idea if I get to the store and realize that the whole thing will end up bulky. Getting some display points would be nice, but in a battle you really need function. :)
Last edited by AquaLepus on Fri Jul 25, 2008 4:05 am, edited 1 time in total.

aEx155
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Re: Arm Mount - First Homemade

Post by aEx155 » Fri Jul 25, 2008 5:09 am

Well, if the LRT isn't going to be bending, then there really isn't any problem.You should just add some for of hose between the two (like you were planning) but put it in a way so that it is inline with your elbow, so that the radius doesn't change. That way, you don't have to worry about length changes.

As for having water storage + LRT case on your back, you could do something like this to save space, or you could just mount the LRT on top of the water backpack. I don't think that would be much of a problem. (I would suggest going this way, since you probably could fit more length then you could on your arm while keeping its mobility)

P.S. I was meaning to ask this earlier, but what instrument do you play? (if you don't mind me asking)

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cantab
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Re: Arm Mount - First Homemade

Post by cantab » Fri Jul 25, 2008 9:09 am

How are you likely to fill the gun?
I'm wondering if you could consider a gun with no reservoir other than the PC's. Just make a double or triple PC out of LRT in pipes that you put on your back. The 3 PCs are connected to each other, and then to a hose leading to a handheld blaster portion. I'd also put a carabiner on the blaster so you can clip it to a belt loop or similar when not shooting. If you're prepared to accept a reduced performance, a hose handle would make a good blaster portion.
To fill this sort of gun, you can either use a quick fill - basically connect a hose attachment to a check valve and on to the PC's, and to fill you just connect it to a tap or garden hose. If you won't have such a source available, you can use a normal pump which takes its intake from a short hose that you just dip in a body of water.

AquaLepus
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Re: Arm Mount - First Homemade

Post by AquaLepus » Fri Jul 25, 2008 2:39 pm

The multiple PC idea sounds interesting, but I'm rather limited by time to get the parts and start construction. Our band camp starts in about a week, and the actual event isn't for several more weeks, but I'll have much less time to devote to non-band things. I'd love to try it out, but maybe when I'm on different limits.

Filling the gun would just be a pump, 2 check valves, and a water reservoir. It really is similar to the SuperCPS. My only major change is that hose for the elbow and perhaps the LRT PC on the back.

As I look at more pictures, it really does seem that having the LRT on my arm would get heavy and annoying - not to mention it sliding around if I don't secure it very tightly. But won't the extra distance [between the pump and the LRT on the back] make for many more pumps than if the LRT was closer, on my arm? Or maybe I should increase my stroke volume beyond that of the SuperCPS to balance?

Also, I just found some hose-type material here and tested it out. I was able to mount it so that it didn't bunch up when bent. What exactly do you mean by inline with my elbow? If your arm is straight out in front of you, and you bend it 90d, I laid the hose right on top (I suppose it is the outside portion of your arm). When the hose was inside the elbow's joint, the tubing bunched and it stretched when it was placed on the exact opposite side. I hope that made sense.. :D
aEx155 wrote: P.S. I was meaning to ask this earlier, but what instrument do you play? (if you don't mind me asking)
I play clarinet in marching band and regular band. This will be my fourth year marching and I'll be one of two drum majors, also. It should be a lot of fun..as soon as I memorize all my music, haha.

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Silence
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Re: Arm Mount - First Homemade

Post by Silence » Fri Jul 25, 2008 3:35 pm

Vinyl tubing will work if it wraps around the elbow. As you said, it kinda runs out of room if it's in the concave part.

A quick release fitting, or any fitting that has parts that can spin, would also work. Orient the "axle" parallel to your elbow's axis so that the two can move in unison.

I'm a senior and I play clarinet too. I'm not sure why you have to memorize music if you're a drum major, though. Do you play for one song and conduct the next? That's a little confusing, I'd imagine.

aEx155
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Re: Arm Mount - First Homemade

Post by aEx155 » Fri Jul 25, 2008 3:48 pm

AquaLepus wrote:As I look at more pictures, it really does seem that having the LRT on my arm would get heavy and annoying - not to mention it sliding around if I don't secure it very tightly. But won't the extra distance [between the pump and the LRT on the back] make for many more pumps than if the LRT was closer, on my arm? Or maybe I should increase my stroke volume beyond that of the SuperCPS to balance?
I guess you would have to pump more, but it would only be to fill up the hose between the pump and the LRT. Since water isn't compressible, you won't have much problem if you connect the pump by a tube. The only problem would be that you have to prime the pump (fill it with water) before you pump, to remove the air in the pump line.

To explain further, you could do two things:

1) Connect the pump cylinder (on your arm) to a check valve + LRT + water tank system (on your back) with one tube. (this is the setup in my first paragraph) Most of the water moves inside the tube, while only the bit closest to the check valves is moved. It keeps it light, but there is a lot of dead space (water that can't be pumped)

2) You could put the pump cylinder, two check valves (on your arm) and connect them with two hoses (to pump (from water reservoir), and from pump (to LRT chamber)). That way, you can have a regular pump; unfortunately, you need one more hose than the other method.

This post has to be cut short, unfortunately. I'll add more when I get back. Hopefully this helps.

zuloon
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Re: Arm Mount - First Homemade

Post by zuloon » Fri Jul 25, 2008 3:57 pm

SilentGuy wrote:
Your water gun sounds similar to the A.R.M. 4000 XL (sorry for no links - there's not much information available out there). It had a pump from the wrist to the shoulder so it could be pumped by one bicep, and a small pressure chamber on the side of the bicep or something. A novelty, if you will.
This is why there's hardly any information about them.

Here's a pic: Image

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SSCBen
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Re: Arm Mount - First Homemade

Post by SSCBen » Fri Jul 25, 2008 4:05 pm

One thing I'd like to note is that LRT can bend when full. It folds and pushes the water from the fold further down the chamber. This only works on a chamber that's not completely full. With that being said, I don't suggest being the tubing because it would create areas of uneven expansion which would eventually not expand when they are much stronger that the rest of the tube due to the degradation of the rubber.
But won't the extra distance [between the pump and the LRT on the back] make for many more pumps than if the LRT was closer, on my arm? Or maybe I should increase my stroke volume beyond that of the SuperCPS to balance?
As aEx said, if you use small diameter piping or tubing from the pump to the LRT there will be no major problem. The "dead volume" only affects the first fill of the water gun--after that it's full of water and does not affect the water gun unless the dead volume is drained somehow.

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Silence
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Re: Arm Mount - First Homemade

Post by Silence » Fri Jul 25, 2008 4:19 pm

Ohio Arts won the suit, though. Hasbro only patented cylindrical rubber tubes thinned in one area to help them inflate in the right direction.

AquaLepus
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Re: Arm Mount - First Homemade

Post by AquaLepus » Fri Jul 25, 2008 5:02 pm

Hm..if I did go with the back-mounted PC, would all the extra bends and turns greatly affect performance? I was hoping to keep the firing portion as linear as possible.

Also, if I use 1/2" PVC piping for the bulk of the barrel and such, should the connective hoses be the same size or even smaller? I was thinking that having a diameter change between the LRT to the hoses and then to the ball valve and nozzle portion would mess up the flow.

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Silence
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Re: Arm Mount - First Homemade

Post by Silence » Fri Jul 25, 2008 5:58 pm

The hose should be much larger, if anything. 1/2" hose barbs have 1/2" outer diameters but 1/4" to 3/8" inner diameters. Get 3/4" or 1" hose, as in SuperCAP. :cool:

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cantab
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Re: Arm Mount - First Homemade

Post by cantab » Fri Jul 25, 2008 10:14 pm

Linear flow is good, but high flow is better. Just use wide hose. 1" would seem to be a bit much though.
A single back-mounted PC can have only the curves of the hose to deal with. Being as they'll be far smoother than pipe elbows, it shouldn't hurt too much.
Basically, don't put in needless bends, but if your physical design calls for a bend then just have it.

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