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PCSR: A new homemade design

homemade new concept redirect bullpup

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#51 Langley

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Posted 12 June 2016 - 12:56 AM

Also, what is the specific mcmaster part you are using to seal the plunger rod? I'm really curious as a decent seal for a 1/2 rod without adding too much extra friction is awesome.

Did this ever get answered? Can't seem to find this anywhere in the thread or the google drive link.


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#52 xXD3V1LXx

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Posted 12 June 2016 - 03:51 AM

Yes it has it uses a k79 seal with a 1 in od. You can find all the mcmaster components for chris' blasters in his build notes.
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#53 Aeromech

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Posted 12 June 2016 - 09:36 AM

Yup! It was in the google drive document called "build notes" in the PSCR folder. But for those wondering, the McMaster rod seal component is 9505K79. This is the only part that you would not have on hand should you be familiar with rainbow builds.


Edited by Aeromech, 12 June 2016 - 09:58 AM.

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#54 CaptainSlug

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Posted 23 June 2016 - 11:44 PM


Modified the piston from an o-ring to a skirt seal piston, because initially it wasn't sealing. If this exercise has taught me anything it's that O-rings are utter shit.

 

 

Part of that issue is that the o-rings used inside stock Nerf Blasters are a lower durometer rating than those you typically buy from a hardware supplier, and getting an o-ring to work the way you want it to requires being able to machine round parts to narrow tolerances.

Having been away from the hobby for a while and coming back to see so many homemades involving relief methods in the plunger head is amusing because we're all 25 years behind Hasbro on the topic. All of the seat surfaces on stock plunger heads are very very slightly tapered and the front face of the plunger heads have cut outs that allow the softer o-rings to unevenly deform and leak when pushed in reverse. I noticed this initially in 2007 while trying to measure a longshot plunger head under the premise of wanting to make one from scratch. And it finally occurred to me as to why the typical blaster plunger head has gaps in the forward face.

 

I think in many ways we're obsessing about some very small things that may or may not make any noticeable difference given how absurd the power level of the springs we are using is. There are conditions where a perfect seal isn't ideal, because the better the seal you have, the more friction it involves.

 

Spring-powered homemades are this weird area where we are trying to achieve pressure through inertia as well as trying to have a good enough seal to build up pressure, but not such a tight one that we can't build enough momentum in the plunger to deliver that pressure in as short of a time span as possible.

 

For instance the HAMP series and many of the bow-arm blasters when you stand back are primarily using raw air chamber volume married with an utter shit plunger seal to achieve pressure in a very short time scale in spite of the excessive air leakage.

 

tl;dr If you do want to experiment with O-rings I would look at "Ultra-Compressible" ones with Shore A50 or so durometer.


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#55 CaptainSlug

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Posted 11 August 2016 - 03:02 PM

I'm on version 5 or 6, I forget which, of marrying snakerbot's redirect with a PCSR. I think I've run out of things to tweak and it's time to just build one.

pcsr_04.jpg

It's a regular Plusbow Rev. 3 catch at the back, but linked to the forward trigger with an aluminum bar. The plunger tube is aluminum, so I'll have to make a 1-1/4 pipe adapter for it by boring out a section of some.

pcsr_05.jpg

Shown with a K14 inside, though I don't have one of those on-hand so I don't know what their minimum compressed length is. If Snoop wants to measure one of those and tell me what the spacing between the coils is I can do the math to figure out. That spring will probably need a different plunger rod length in order to reach the catch plate.

 

Nothing here is 3D printed. Everything will fit onto a single square foot of 0.230" thick polycarbonate with some room to spare. The whole front half of the blaster can be removed by simply removing two screws.


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#56 Meaker VI

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Posted 11 August 2016 - 03:51 PM

Nothing here is 3D printed. Everything will fit onto a single square foot of 0.230" thick polycarbonate with some room to spare. The whole front half of the blaster can be removed by simply removing two screws.


Dang it slug, I'm not even done building the 3d printed version and you make a non-3d printed version. Now what am I supposed to do with this massive 3d printer?
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#57 CaptainSlug

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Posted 11 August 2016 - 03:55 PM

Dang it slug, I'm not even done building the 3d printed version and you make a non-3d printed version. Now what am I supposed to do with this massive 3d printer?

Print stuff?

 

There are plenty of non-structural parts that can be printed without worrying about layers de-laminating.


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#58 Meaker VI

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Posted 11 August 2016 - 09:00 PM

Print stuff?
 
There are plenty of non-structural parts that can be printed without worrying about layers de-laminating.


Oh I know, I jest. There are, in fact, plenty of structural parts that can be printed without trouble so far as I can tell, you just have to print it big/strong enough.
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#59 Snoop Doggy doge

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Posted 17 August 2016 - 03:32 PM

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K14s have a 3/8 space between each coil, each coil is 1/8 wide.

The 3D printed prototype I currently ahve my hands on is holding up fine, even with my abuse. I know the redirect piece has been updated, but I was intrigued by Kanes newest redirect piece for his ESLTs and would be curious if anyone with a printer would redo the files to accomadate and work in a PCSR.

The pieces I know that have to be strong are the stock, sear, redirect piece and plunger assembly. Those take the most stress and I also added a polycarbonate safety plate on the back of my PCSR before I added foam so just incase anything breaks, there's something else to buffer it. However since I have the extended draw version, it has a stupid long stock. 


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#60 CaptainSlug

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Posted 17 August 2016 - 08:12 PM

My PCSR is roughly half finished at the moment. The back half and middle are basically done (grip, redirect, trigger) I just need to make the front half tomorrow. I'll probably have it completely finished before the weekend. A full write-up won't be forthcoming until I make a second one however, but i will provide a full set of templates by early next week until I can get around to making a second one.

 

The first blaster always involves too much refinement and revision to really make a good write-up out of it.

K14s have a 3/8 space between each coil, each coil is 1/8 wide.

Thanks. McMaster does provide a CAD model of their springs, but I haven't found those models to be particularly accurate. I've also had some infrequent issues with them shipping me the wrong springs in the "correct" packaging too. But returning things to them is as easy as shipping them back with your name and return address on the box.

The downside is you end up paying the return shipping, and justifying the cost of that depends on the value of the item.


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#61 Snoop Doggy doge

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Posted 17 August 2016 - 11:25 PM

No prob, sorry about being so late but I got so caught up doing work for other things after APOC and I have a lot to catch up on NH. Now I'm getting lazy and I still got summer HW, RIP me,

 


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#62 Meaker VI

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Posted 18 August 2016 - 02:34 PM

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Finally took the hour to put everything together:

 

IMG_1916.JPG

 

Works ok, considering I kludged most of the parts. I used an oring instead of a skirt seal with my plunger head, a rubber grommet I found instead of a seal in the pusher-redirect, oak dowels instead of nylon (though that is probably less of a kludge, they seem to be doing their part just fine), an RSCB instead of a Y, and the list probably goes on. Unfortuneatly, the RSCB doesn't attach the way the Y does so the front support I griped about doesn't fit. Womp-womp.

 

My really sketchy range test puts an elite sucker dart out of that RSCB at around 21 paces. A triad fired the same way with the same dart went 16 paces.

 

Notes/Comments:

  • The built is *super* easy to put together, once you have the parts in front of you. The parts are not all easy to acquire though, ideally you'd need a McMaster order, a 3d printer/order, and a trip to the hardware store for 1-1/4" PVC, 1-1/2" PVC, 1-1/2" 200 PSI PVC, and 1/2" CPVC (even if you're using something else for the barrels, you need a stub to plug into the blaster). Most of the machining is easy, but requires some attention.
  • The trigger is tricky and finicky. Partly this is due to my changes, but partly due to the blaster's design:
    • You need a slot cut in the 1-1/4" PVC to accommodate the sear, but because it's in a solid printed part, the position it needs to be in is really hard to judge. A cutting template would help, but you'd also have to take care to drill the stock/trigger holder part into place after cutting so you know for sure the sear fits correctly. I'm pretty sure I used a 1/2" drill bit to make the slot that the sear rides in and cleaned up the holes by tipping the drill, and then followed up with a knife.
    • The part *I* may have caused is the pull - it is stiff. But again, I'm using my own plunger head that uses an oring instead of Aeromech's that uses some kind of fancy seal.
    • Another finicky bit - the connection between the trigger and the plunger is difficult to work out, again because the trigger sear is completely encased in a printed part that needs to stay firmly attached to the PT. I suppose using a clear PT would help with this, but deciding how much length to put on the trigger rod took experimentation, and then figuring out where to attach the trigger took more experimentation. My version does not have the trigger stopped in any way from just falling out of the blaster, which is fine for my experimental use, but not ideal for a production/war ready blaster.
  • The stock terrifies me slightly. It shouldn't just explode, but there is a lot of force being put onto that printed piece. Putting a PVC spring-retention ring in wouldn't be hard and would probably make the stock qualms less relevant.
  • The grip feels awesome and solid (I didn't print it solid, it just feels solid - I think I used 1.6mm walls w/20% infil and printed with support. The end touching the grip-clamp was down), but the attachment was a bear. I'm not actually sure how Aeromech did it, but I drilled out the holes that are on the inside and screwed it on from outside. Remodeling that for better/easier attachment would be preferable.
  • Aligning the grip and the stock is very important and shouldn't be rushed, I may have a sticky trigger because mine doesn't align perfectly.
  • Many of the printed parts suffer from a similar, difficult to avoid, problem: You've got holes pre-drilled in them, and you really need to use those holes (and only those!) because the printer put extra material there. But you can't *see* those holes when you're driving your screws, so you need to figure out a way to transpose the marks from a printed piece to a non-printed piece. I didn't do it for the front grip (not shown, pressure is enough to move the PH-pusher forward, a screw sticking out does the rest), did it for the support (but then had to take it off anyway to put the front grip on and it wasn't doing anything), and drilled out the grip so I could attach it from the outside. Short of more printed pieces, I'm not sure how you'd get around the issue elegantly. Templates are a possible inelegant solution.

All-in-all, it's a cool blaster and you should build one if you've got a printer and can get the right parts. It isn't as plug-and-play as it looks, but the machining time is pretty trivial once you figure out a way to get it done. If you don't have a printer, wait for Slug's version, which looks like it'll trade printer time for your time, but then be easier to assemble when you're done cutting it out.


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#63 CaptainSlug

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Posted 18 August 2016 - 03:39 PM

Just taking my sweet time. The trigger linkage needed a bit of fiddling to get all the mechanical resistance and fit right. It has to use two weak return springs in order to have enough travel and not be sticky. May simply be because I screwed up the rotation moments a tad and should probably have reversed them beforehand.

pcsr_07.jpg

I also managed to do a crap job drilling the 5/8" hole for the cpvc stub. I really should have used the mill for that and it will have to be resolved on this prototype with some thick cyanoacrylite epoxy.

 

Notice that the plunger tube is floating. All the load-bearing for the spring is external to it so that you do not have to drill through-holes in the plunger tube for anything other than venting. I've had a few too many polycarbonate plunger tubes develop fractures underneath the screws.


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#64 Snoop Doggy doge

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Posted 18 August 2016 - 07:51 PM

mmmm that non printed PCSR is looking good,


Meaker, put a plate of polycarb behind the stock to create a buffer just incase, if you don't like the fear of a spring resting on a printed piece. 
Also, a trigger stop is just a screw in front of the trigger, I don't know if it's drilled in but I could take pics for you as it's not very hard to implement. 
The front rod seal by the way, curious how you implemented it or modified the design because that seal would be very hard to o ring, especially if it's not a modified piece to hold the seal in place

If you have any dimension questions you should probably ask me as I have THE PCSR unless Chris built another one, and I have fixed it and field stripped it entirely to the bones. 


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#65 Meaker VI

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Posted 18 August 2016 - 10:15 PM

Meaker, put a plate of polycarb behind the stock to create a buffer just incase, if you don't like the fear of a spring resting on a printed piece.

 

I'll probably figure out something to put there. It is a bit unnerving, especially since I've launched the PT across the room while disassembling it.

 

Also, a trigger stop is just a screw in front of the trigger, I don't know if it's drilled in but I could take pics for you as it's not very hard to implement.

 

Not hard, but fiddly - that is, it's a pain to get right but it's just time spent on the bench doing it. I'll maybe get around to adding it if all it is is a screw.

 

The front rod seal by the way, curious how you implemented it or modified the design because that seal would be very hard to o ring, especially if it's not a modified piece to hold the seal in place

I used a rubber grommet. It looked like this one, but fit the dowel I used. It was just the first thing I found, if I put a mcmaster order together I might get the proper thing instead because I suspect this still isn't tall enough to fully seal the PT. The oring is on the PH I made, which I think is upthread.


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#66 Snoop Doggy doge

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Posted 18 August 2016 - 10:56 PM

*sigh* I'm really tired from that whole noob thread but here. This is how the trigger is held in
I really don't know how come yours may be doing terrible, but part of it I think is the seal rod is wood and that's not great for holding a seal. Also, why oring? Anyway here's how the trigger held on

image1-3.JPG


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#67 Meaker VI

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Posted 18 August 2016 - 11:45 PM

*sigh* I'm really tired from that whole noob thread but here. This is how the trigger is held in
...Also, why oring? Anyway here's how the trigger held on


I'd seen that set of holes and guessed at its purpose. Getting it to seat while still having enough range of motion to activate the sear means I've got to mess blindly with getting the rod length *just* right. Like I said, it's fiddly.

 

Which makes me realize something - making the sear have excessive range of motion would result in a less fiddly part.
 
Oring PH because A ) I had it and B ) I didn't have a cup seal.
 

I really don't know how come yours may be doing terrible, but part of it I think is the seal rod is wood and that's not great for holding a seal.


It's because the seal isn't filling the printed part, and possibly problems with the PH (Which I admitted might be a problem, since I drew it for my setup and just used it in this system). The wood is as smooth as any plastic rod, and as long as I keep it lubricated should hold a seal just as well in this case.

Actually, I should redraw it off the PSCR files now that I've got them, that'd probably result in a lighter trigger pull.


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#68 CaptainSlug

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Posted 22 August 2016 - 03:30 PM

I had to work on Saturday and was too exhausted to get much done on the blaster afterwards. The fiddling I did do helped me determine that the catchplate is screwed up, so I just finished replacing it and everything is working fine now.

 

Spring guides inside the spring are not working as well as I had hoped in this configuration, though I won't know if it's really an issue until I finish making the front half of the blaster. And until I do that I'll have an only slightly dangerous 1/2" delrin rod shooting spear-gun.


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#69 CaptainSlug

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Posted 23 August 2016 - 12:58 PM

It's in one piece. Sorry for the shit photo. I'll take more tonight.

pcsr_08.jpg


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#70 DjOnslaught

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Posted 23 August 2016 - 01:20 PM

It's in one piece. Sorry for the shit photo. I'll take more tonight.
pcsr_08.jpg


I really dig the look of the blaster Slug
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#71 CaptainSlug

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Posted 23 August 2016 - 04:03 PM

pcsr_09.jpg

Testing begins tomorrow. I still need to make a spring guide insert.


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#72 shandsgator8

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Posted 23 August 2016 - 04:47 PM

I'm not one for homemades, but I gotta admit, that's a cool looking piece of engineering.


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#73 CaptainSlug

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Posted 24 August 2016 - 11:02 AM

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It's completely done, here it is with the spring guide. I will post a new thread once I have a construction write-up done.

But for now, here are the templates and partlist.

 

PARTSLIST

 

TEMPLATES

 

 

pcsr_10.jpg

I'm going to be making grips without the upper rest from now on. There's no point in one being there on a platform that doesn't have recoil and they're the source of all of the relative difficulty people are having with sanding their grip panels enough to be comfortable.

pcsr_11.jpg

The center of mass is nicely placed just above and behind the grip on this design. The ability to take-down everything without any tools is also pretty nifty. Snakerbot's redirect is working perfectly too.

pcsr_12.jpg

In making this I discovered that my catch plates were much more complicated than they needed to be. A 9/16" through hole works perfectly fine and doesn't required as much travel. It just need to be precisely placed relative to the edge that the trigger linkage pushes on.

pcsr_13.jpg

The lower stock rod is acting as a tension member against the spring load. So I've switched to just using a long screw and a thumb nut to secure it to the bottom of the grip.

pcsr_14.jpg

Length tolerances on a few of the parts can be fussy and it took some time to get the pump-grip, plunger, front tube, and so on all interacting perfectly. The pusher rod has to be long enough to push the plunger back, but short enough that it retracts to a position that won't impede the plunger firing. And if it's too short the end of the pusher rod is too close to the redirect seal.

All of these interactions also impact the dimensional requirements for the length of the slots in the front tube, the plates mounted inside the grip, the length of the grip itself, the placement of the catch on the end of the plunger rod, etc.

 

But with the whole front half of the blaster being so easy to remove, adjusting most of these is a piece of cake.


Edited by CaptainSlug, 24 August 2016 - 03:43 PM.
partlist and templates added

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#74 Meaker VI

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Posted 24 August 2016 - 05:18 PM

Looks good as usual slug.
 

I'm going to be making grips without the upper rest from now on. There's no point in one being there on a platform that doesn't have recoil and they're the source of all of the relative difficulty people are having with sanding their grip panels enough to be comfortable.

 
I'm working on mimicking the TTG handle in 3d so I can print handles I like, and I noticed it has the upper rest. Maybe a shouldered platform doesn't need the rest, but I feel like a pull-back that isn't shouldered might - the pull back action should torque the blaster against that part of your hand/thumb and having a rest there seems way more comfortable than not. Could easily be a dashed-in "do this if you like sanding" part though.
 

In making this I discovered that my catch plates were much more complicated than they needed to be. A 9/16" through hole works perfectly fine and doesn't required as much travel. It just need to be precisely placed relative to the edge that the trigger linkage pushes on.

 
I was looking at another project and was thinking basically the same thing. Glad you tried it and it works as expected, I'll keep that in mind for the other project.
 
By the way, do you find pivot triggers or slide triggers to be better? It seems like a slide would be easier and fewer parts, again looking at production NERF blasters.
 

Length tolerances on a few of the parts can be fussy and it took some time to get the pump-grip, plunger, front tube, and so on all interacting perfectly. The pusher rod has to be long enough to push the plunger back, but short enough that it retracts to a position that won't impede the plunger firing. And if it's too short the end of the pusher rod is too close to the redirect seal.
All of these interactions also impact the dimensional requirements for the length of the slots in the front tube, the plates mounted inside the grip, the length of the grip itself, the placement of the catch on the end of the plunger rod, etc.
 
But with the whole front half of the blaster being so easy to remove, adjusting most of these is a piece of cake.

I think that's the PSCR flaw - it's a great platform, but it *is* finicky about how long things are.


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#75 CaptainSlug

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Posted 24 August 2016 - 05:57 PM

By the way, do you find pivot triggers or slide triggers to be better?

I like that sliding catch plates take up less space and less material. Any other criteria seem to be a matter of personal preference.


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