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"In the world of spuds today"

A place to ask general spud cannon related questions.
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Unread postAuthor: mark.f » Sun Mar 30, 2008 11:04 am

DYI wrote:I don't know what kind of school you go to SB15, but at our school, that is the advanced Grade 11 level. And by using that formula, I came out with an answer of 0.19635 units2 :?


Are you using n=16 and r=10, (r being the radius of the circle the polygon is inscribed in)?

If so, then I don't know why you'd be getting that off of an answer. Are you in radian mode on your calculator?

That formula again is Area = nr<sup>2</sup>sin(pi/n)cos(pi/n)

Also, make sure you use parentheses correctly for the trig formulas.
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calcs.jpg
Here's the calculation in Open Office, (similar enough to Excel). Default for SIN calculations is in radians.
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Unread postAuthor: LikimysCrotchus5 » Sun Mar 30, 2008 1:47 pm

"In the world of spuds today"

Its getting warmer outside (at least where i live) so in the spirit of spring i decided to go shoot my advcanced combustion.

And let me tell you that i have been getting the performance that all of you guys talk about here. It worked out very nicely. My psi i add to my chamber is 62-63 psi and then after that i add air to the mix by opening the back and let the fan run for 2-3 seconds. Its getting that big bang effect even though my C:B ratio is 1:1 which was what i learned as optimal although .8:1 is also good. But either way, i am satisfied at how high potatoes can fly.

I would say that its airtime might have been around, lets say 10-15 seconds. Then it landed in my nieghbors front yard, luckily he wasnt outside. Now i gotta find a less urban area to shoot that beast.

Also my 4 inch piston valve should be done sometime soon. I have a 10 ft section of 4 inch pipe but i dont think i am going to use the whole thing for the chamber but most of it will be. I currently have a undersized barrel so i think i am just going to buy a 10 ft section of 3 inch pvc pipe rather than just a puny 4ft barrel. And i need a barrel support, any ideas besides wood?
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Unread postAuthor: DYI » Sun Mar 30, 2008 3:39 pm

I would say that its airtime might have been around, lets say 10-15 seconds.


Really? Because the SCTBDC can get an absolute maximum of 15 seconds hang time with a spud, and that's at about 1,100 fps, using what is likely a very optimistic drag coefficient.
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Unread postAuthor: LikimysCrotchus5 » Sun Mar 30, 2008 4:48 pm

When do you begin to measure its airtime?

I never officially counted, but i guesstimated from the time of when it left the barrel. Im guessing that you count the seconds when it starts to fall after it reached the highest point it could achieve.

So then i would say that the airtime maybe 6-10 seconds? That sound reasonable?
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Unread postAuthor: SpudBlaster15 » Sun Mar 30, 2008 9:59 pm

I've achieved hang times of about 15 seconds with all of my advanced combustion launchers using potatoes as ammo. The estimated muzzle velocity for each launcher is around 600fps.

DYI, keep in mind that drag force is proportional to the square of velocity. Since I don't know the specifications of your ammo, I can't give you an exact figure, but given the high drag coefficient of a potato slug; with 4x the initial drag force acting on it, I speculate that your projectile will not have covered a very large distance before it has decelerated to similar velocities as what an average advanced combustion launcher can produce.
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Unread postAuthor: LikimysCrotchus5 » Sun Mar 30, 2008 11:24 pm

Yay i got a supporter :)

This combustion shot was seemed to be a bit more powerful than some of the others. I watched it fly straight out of the barrel, then curve slightly because of the speed and its shape, then it ended up flying backwards.

But his was a just about complete vertical shot. But i did use a potato that fit 2 inch sch 40 pvc with a 114 inch barrel length, IIRC.
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Unread postAuthor: DYI » Thu Apr 03, 2008 6:35 pm

In the world of spuds today, I got some interesting equipment from McMaster-Carr (which had to go through USPS, Zep, UPS, Muskoka Delivery, Canadian customs, and a man by the name of Phil Wight to get here).

This includes all of the specialty bits for my new hybrid metering system, as well as a QEV that I got for a quick valve option (works quite well).

The gauges are, to say the least, quite impressive, with 4" faces and weighing about 2 pounds each, and that 1/2" ball valve has "2000WOG" printed on the side :D

Image

A 4 000 psi $60 pressure washer handle is a bit of an overkill pilot valve for a 150 psi QEV gun, but it's been disused and needing a new launcher after I realised that it wouldn't seal with 2.4kpsi helium.

Image

Quite fun shooting, but essentially the same as any QEV gun, and not worth making a topic about.

Image

And finally, I present the new concrete breach for the SCTBDC. I don't like it when parts break at 500 psi, and I won't allow it to happen again.

Image

Who said ABS bell reducers aren't rated for 500 psi? :D

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Unread postAuthor: starman » Thu Apr 03, 2008 6:44 pm

DYI wrote:In the world of spuds today, I got some interesting equipment from McMaster-Carr (which had to go through USPS, Zep, UPS, Muskoka Delivery, Canadian customs, and a man by the name of Phil Wight to get here).

And finally, I present the new concrete breach for the SCTBDC. I don't like it when parts break at 500 psi, and I won't allow it to happen again.



LOL...OK I'm still laughing at that concrete chunk you have there...looks like you just unearthed your mailbox footing or something. Yes, 500 psi should be a breeze now.

Dang, customs is a bear isn't it. Are there no suppliers of this stuff anywhere in Canada?
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Unread postAuthor: bigbob12345 » Thu Apr 03, 2008 6:49 pm

God i need to get my hands on one of those 1/2in ball valves rated to 2000psi.Then a 15x hybrid may be a possibilty. and a part number for it would be nice
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Unread postAuthor: pizlo » Thu Apr 03, 2008 6:57 pm

Ah DYI you can set my mind at ease, is that QEV this one?
Part: 6646K23
I know Mcmaster images aren't acurate, but it would seem that the pilot would be on top of the valve(in the position you have it there). So is this the one?
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Unread postAuthor: DYI » Thu Apr 03, 2008 7:00 pm

LOL...OK I'm still laughing at that concrete chunk you have there...looks like you just unearthed your mailbox footing or something. Yes, 500 psi should be a breeze now.


I don't half do anything :lol:

I haven't got the bill for customs yet, but last time it was more than the entire order had cost :(

@Bigbob: The ball valve is listed under "steel and SS" ball valves on McMaster, but I can't be bothered to look for a part number right now. The 1/2" valve cost $25.54, which might not be too easy to swallow with your current "pay". The gauges were a steal, at $35 each.

@Pizlo: there's only one type of QEV useful for spudding available on McMaster (the rest vent to the atmosphere), and that's the one I got. It is configured properly, as I've already shot it 10 times (and accidentally hit my neighbour's window once :roll: ). The port labeled "EXH" is what we would refer to as the barrel port.
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Unread postAuthor: pizlo » Thu Apr 03, 2008 7:04 pm

Image
this is all I have to go on, and you have the number in my other post, is it this one?
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Unread postAuthor: DYI » Thu Apr 03, 2008 7:08 pm

Yes, it is.

I won't get around to putting the hybrid together until Saturday, as I'm not doing anything half-assed on the meter; if the weld on the back plate was bad and it broke off when I did a test fire, well...

The lowest that I can really expect this to work at is 5x or so, and even that may be pushing it. The reasoning behind a 0-15 psi gauge was that, after I make sure it works, I can cast concrete or aluminum around the whole contraption, and bring it to 20x (~12.8psi fuel pressure by the current thinking). That, and the 0-10 gauges cost more, and were less accurate :roll:

An interesting tidbit: the 0-15 gauge is so accurate across the whole scale that you can move it significantly by blowing on the opening, and its needle actually moves with natural changes in ambient pressure (as is evidenced by the fact that it can vary about 1kPa or so depending on the weather :shock: )
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Unread postAuthor: Ragnarok » Fri Apr 04, 2008 8:13 am

INWOST, whether or not you noticed me leave, the 'Rok is back.
I've been in Spain since last Tuesday, and got back at stupid o'clock yesterday, so you won't have seen any posting from me since last Monday, as my laptop stayed at home.

The break itself was nice enough. The wind was a bit of a problem, but it was certainly good for sailing and kite flying - if not the bikes we hired.
Made the return flight a little interesting too, not great for someone like me who's not a fan of such things anyway.
Also ended up with, like I always do, sunburn. I'm particularly susceptible to such things.

Anyway, I'm back, with the usual shed load of nutty ideas.

DYI wrote:An interesting tidbit: the 0-15 gauge is so accurate across the whole scale that you can move it significantly by blowing on the opening, and its needle actually moves with natural changes in ambient pressure (as is evidenced by the fact that it can vary about 1kPa or so depending on the weather :shock: )

Quite a weird effect, and one you'll only ever see in sealed gauges (glycerine filled or those filled with other fluids). A dry gauge, being unsealed, won't ever exhibit such a phenomenon.

...Yet another mildly useless piece of information.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: Jared Haehnel » Fri Apr 04, 2008 8:26 am

I did notice your absence hopefully you had a good trip 8)
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My current projects....

Currently buying part for...
http://www.spudfiles.com/forums/my-new- ... rt,15.html
Still on the drawing board...
C02 tank hybrid
Screen doors for submarines...
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