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spudgun range, are we falling short?

A place to ask general spud cannon related questions.
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Unread postAuthor: drex » Mon Apr 25, 2011 5:36 am

I think I will make that, it will have to wait till next week after a robotics competition.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 25, 2011 6:56 am

That would be sweet :) I would taper the tail to match the nose, and give the fins a streamlined section:

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Unread postAuthor: the unit » Mon Apr 25, 2011 7:35 am

Would porting the end of the barrel help with accuracy? That way the sabot should be slowing down and separating from the projectile while they maintain their axis because they are still in the barrel.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 25, 2011 1:16 pm

the unit wrote:Would porting the end of the barrel help with accuracy? That way the sabot should be slowing down and separating from the projectile while they maintain their axis because they are still in the barrel.


I don't think porting will have that effect. What could be done, if one had the tools and materials, is choke the end of the barrel in such a manner that the sabot encounters friction at the muzzle, slowing it down before exiting.
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Unread postAuthor: ramses » Mon Apr 25, 2011 3:22 pm

jackssmirkingrevenge wrote: is choke the end of the barrel in such a manner that the sabot encounters friction at the muzzle, slowing it down before exiting.


Without touching the fins. As far as supporting the nose of the projectile, a flower pedal sabot would be useful there. It wouldn't see much force or pressure, so it could probably even be styrofoam or similar. This would interfere with the choke, though.
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Unread postAuthor: dewey-1 » Mon Apr 25, 2011 3:38 pm

Just for JSR and his military projectiles.
If any one wants a CAD file just PM me!

edit for: any one wants
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 25, 2011 4:35 pm

dewey-1 wrote:Just for JSR and his military projectiles.


Beautiful Duane, makes me want to deplete some uranium!

ramses wrote:Without touching the fins. As far as supporting the nose of the projectile, a flower pedal sabot would be useful there. It wouldn't see much force or pressure, so it could probably even be styrofoam or similar. This would interfere with the choke, though.


Here's another variation of what I had in mind, the idea is not to stop the sabot, but slow it down enough for the projectile to slip free before the sabot leaves the barrel. With sufficient porting as the unit suggested, it might just work.
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Unread postAuthor: LeMaudit » Mon Apr 25, 2011 5:00 pm

A variation of the idea, maybe more feasible to build quickly, without over-engineering the barrel muzzle (please note that I didn't say that I didn't like that :D )

The shock from the sabot to the end cap slow it down and set the projectile free.

Of course a bit of friction/tape/whatever (except epoxy) to hold the cap tight might help.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 25, 2011 5:14 pm

LeMaudit wrote:without over-engineering


:shock:

Nurse! He's out of bed again!
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Unread postAuthor: the unit » Mon Apr 25, 2011 6:06 pm

I think the porting idea has some merit. Take the last foot or so of the barrel and see if it helps, if not it can always be used to make an integral suppressor ;). Also if it doesn't work on its own we could add in friction as you suggested.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 26, 2011 12:58 am

the unit wrote:I think the porting idea has some merit. Take the last foot or so of the barrel and see if it helps, if not it can always be used to make an integral suppressor ;). Also if it doesn't work on its own we could add in friction as you suggested.


I don't think porting alone with work, because if the friction on the sabot isn't dramatic to some extent, sabot & projectile will likely stick together and slow down as a system. In this case I think LeMaudit's idea is a valid one.

The ported gas can be put to work though as per the concepts below, by pressurising a space at the muzzle that then:
1) pushes on a series of ball detents
2) pushes on pistons
3) pushing on an annular diaphragm
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Unread postAuthor: MrCrowley » Tue Apr 26, 2011 1:08 am

Hey LeMaudit, have you finalised a sabot design yet?

In other news I added an extra 15cm to the chamber since the 1.5" ball valve blew its seals and I needed a way to extend the chamber so I can put a barrel support further up the length of the barrel.

I also fixed my 'high' volume track pump by adding an extra o-ring to the piston since the old o-ring had been worn down. My track pump has now had four hose replacements, a homemade stand, refitting, retapping and reorganisation of the input/output/gauge manifold to accommodate the new fatter hose and a piston o-ring replacement. It's a Frankenpump compared to its old self, but hey, it still works.

I'll also buy some glowsticks and KNO3 (for smoke) to run some experiments and see whether if either of them are worth using on launch day.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 26, 2011 2:15 am

MrCrowley wrote:Hey LeMaudit, have you finalised a sabot design yet?


If only we would give him a final design :)

... on to his previous idea, it might be possible to stop the sabot without destroying both sabot and launcher by forming an air cushion. Here are several configurations that might work with the air cushion area denoted in cyan. The last one is the simplest as the sabot itself forms the air cushion and in practice would probably mean that sabot and muzzle plug never actually physically touch.
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Unread postAuthor: LeMaudit » Tue Apr 26, 2011 6:45 am

If only we would give him a final design

There is truth it that...

Hey LeMaudit, have you finalised a sabot design yet?

I have cut 4 rectangular petals with a snowing effect, and before I build dewey-1 drawing, I will first try to cut deep slots in a UHMW disk and see how it feel with this separation ploy we discussed. If I think the friction only could work to keep everything together, maybe I could send you the sabot so you can try it, with a mockup ammo (I promise the mockup will not be shiny... I'll do my best ;-) ).

But I must confess I was very weak during this long week-end, and spent most of my time buying some new attachment for my tools, pimping my lathe and mill with wowing new capabilities. Then I went to a phase of depression and drank, to forget their price :D

So, let's hope I'll work on more stuff when I'm sober, most certainly during the week :-)
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Unread postAuthor: LeMaudit » Fri Apr 29, 2011 5:26 pm

Looks like it could work with a thick UHMW grooved plug :D

Image

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Plug diameter is 48mm, just a tad smaller than the bore, because the friction should came from the petals edge only. The petals are right now too big, because I need some material to support the cut later. This is why I weighted only two + the plug.

Weight should be around 50 grams, maybe less with some appropriate holes here and there... depends if I add an aluminum back plate, MrCrowley seemed to think if would be necessary to avoid melting the UHMW.

I'll try to work during the week end forming the petals to support the MiniBoy.
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