NerfHaven: Under-Compensator writeup - NerfHaven

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Under-Compensator writeup In which I get off my lazy ass to contribute something non-trollish.

#1 User is offline   Exo 

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Posted 23 April 2012 - 11:58 AM

This is the Under-Compensator. It's awesome. It shoots. I suggest you make one, so you can fully experience the awesomeness.
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Stuff you'll need:
1.5" PVC (at least 2', but you can go longer)
1.5" PVC tee, coupler (one of each)
1.5" to .5" bushing/reducer (three of them)
Some .5" PVC, all of it drilled out with a 5/8" spade bit
CPVC, long enough for the plunger rod, I didn't take measurements, but it all depends on how long the entire thing is.
Something to be used as a plunger handle.
Plungerhead stuff, Mine is simple to replicate if you know what you're looking at, but you don't have to use my design.

Tools:
A saw
A file
A Dremel OR A drill
A pair of those awesome scissors, but you can use a half-round file or a sanding drum on a dremel in a pinch. (This is only required if you're using my plungerhead, this isn't necessary if you are using o-rings or a traitional HAMP seal.)

Let's begin.

Cut a length of the 1.5" PVC. To do this, figure out how long you want the draw to be, and add an inch to compensate for the length of the plungerhead.
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Then, bevel the inside edges, on both ends of the pipe. This is only neccesary if you are using "my" plungerhead, or the same type of seal. Also, as an added touch, you can lightly sand the outer edge so that the PVC fittings can be easily removed, but not so sanded that they will fall off under normal use.
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Then, put one bushing inside the coupler, and two bushings in the tee. On the tee, one of the bushings should be on the "arm" of the tee, and the other should be on the "leg" of the tee. Also, take a ring of the .5" PVC that has been drilled out, and place it in the bushing that is in the "arm". The CPVC should be both relatively un-frictiony and relatively sealing with this ring.
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You may attatch the plunging handle now, if you wish, or it can wait till later.
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The next few prictures are all about the plunger head. Mine is designed so that it will seal perfectly in both directions. It is also not rotationally connected to the PVC fitting that holds it. This allows me to twist the plunger rod as much as I wish without un-screwing the seals. In the first picture, the PVC ring that I later added is critical, it keeps the plunger head from pulling out of the tube and into the tee. I would suggest that this ring be about .75" long. Mine is a bit smaller, but it still does what it needs to do. You do not have to use that particular fitting, that .75" bushing is all I had at the time. The nut in the middle of the double seal helps with the final assembly as well as maintaining the "tightening" of the seals. The bolt is 2.5" long.
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Then, once the seal is fully built, remove the "top" or "front" seal, slide the plunger rod and the "lower" or "back" seal (while on the plungerhead) through the ring in the tee, then place the plunger tube over the seal, checking that the seal contacts the walls correctly, The beveling helps with that, and then slide and connect the plunger tube into the tee. You should now have this:
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Now, re-attach the "top" or "front" seal, make sure that it will contact the walls correctly, lube with your choice and attach the coupler and bushing. I use white lithium grease. It's cheaper than silicone grease, and for this large draw and contact surface, you'll need a good bit of it. It may dry out, but this thing isn't difficult to re-lube, and the perfect seals are worth it. The "forward" stroke has a perfect seal, but my "back" stroke seal isn't, due to the 5/8thed PVC ring and CPVC combo, but it's good enough that I can fire the same stuff with about the same effort and air efficiency.
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One thing I have noticed with these seals is that they like to "pop", and they will have a part that has bent inward, so it no longer contacts the walls all the way around the seal. But, if the seals are left for a few days while correctly contacting the walls, the rubber washers will shape themselves into a tempermanent cup shape. If left out, they will resume their original flat shape over the next few days.

I really liked the concept behind the original Compensators, but they were just too big for my taste. This thing is much lighter, more compact, more portable, and is fairly easy to construct and use.

This post has been edited by Exo: 23 April 2012 - 12:00 PM


#2 User is offline   Jilliop 

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Posted 23 April 2012 - 12:10 PM

I like this, although it still seems a tad large, but I've never heard of the original compensator. I'd love to compare/contrast and see your improvements, but a quick search didn't merit anything. I'll dig deeper, but do you happen to have the topic handy?

#3 User is offline   Bchamp22795 

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Posted 23 April 2012 - 01:15 PM

View PostJilliop, on 23 April 2012 - 12:10 PM, said:

I like this, although it still seems a tad large, but I've never heard of the original compensator. I'd love to compare/contrast and see your improvements, but a quick search didn't merit anything. I'll dig deeper, but do you happen to have the topic handy?


Original Compensators are Dual Action Hamps. Both the forward and backward stroke fire 3-4 darts at a time around 100ft.

The First: http://www.youtube....VKVHEwHw Click
Updated: http://www.youtube.c...h?v=H3cfhE5JH9w (skip to 58 seconds)

Note: Links are relevant, not plugs.

This post has been edited by Bchamp22795: 23 April 2012 - 01:16 PM


#4 User is offline   Jilliop 

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Posted 23 April 2012 - 01:37 PM

This whole thread just made about 110% more sense. Thanks a bundle!

Also, this is rather brilliant and I'm quite impressed :)

#5 User is offline   Exo 

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Posted 23 April 2012 - 06:02 PM

Thanks, I'm glad it's been well received so far. Yes, it's rather large, I don't think I'd use it in a war setting, but that's just my opinion on all HAMPs. I was considering doing a much smaller 1" version later, as that could be a useful integration.

#6 User is offline   KaneTheMediocre 

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Posted 25 April 2012 - 04:34 PM

View PostExo, on 23 April 2012 - 11:58 AM, said:

This is the Under-Compensator. It's awesome. It shoots. I suggest you make one, so you can fully experience the awesomeness.
Posted Image


I'm unsure if this is intended to just be a double-action HAMP, or to be a double-action-burst-firing HAMP. Based on the plunger size and seal, either seems plausible depending on your barrel setup. Which brings me to my next question--How are you attaching the barrels and hoppers to the plunger tube (Aside from the obvious plumbing connections)? Do you think you could post a pic with the whole blaster put together?
RAINBOW CLAN FTW
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#7 User is offline   Exo 

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Posted 26 April 2012 - 06:24 AM

View PostKaneTheMediocre, on 25 April 2012 - 04:34 PM, said:

I'm unsure if this is intended to just be a double-action HAMP, or to be a double-action-burst-firing HAMP. Based on the plunger size and seal, either seems plausible depending on your barrel setup. Which brings me to my next question--How are you attaching the barrels and hoppers to the plunger tube (Aside from the obvious plumbing connections)? Do you think you could post a pic with the whole blaster put together?

I like to keep my setups ambiguous, except in cases that would benifit the most from a solidly attatched barrel instead of a coupler, but there's only one way I'd consider using this, BUT, I'm not going to permenanlty attatch the stuff, just so I can use the stuff on other things, and it makes storage and transportation simpler. Anyways:
Posted Image Those are GRSBs, they feed well. Sorry, I know the picture's fuzzy, but you get the general idea. Of course, the barrels aren't as long as tehy could be, with the 12" barrel, it hits 50-60".

This post has been edited by Exo: 26 April 2012 - 06:24 AM


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