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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: Mr.Sandman » Sun Aug 17, 2008 6:51 pm

MaxuS the 2nd wrote:Anyone know where I can get a 250mm piece of 90mm Delrin rod?
Uk only really.

Edit: Never mind, seems it's also known as Acetal.


mcmaster? not surewhat is in the uk
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Yeah, it's that important.
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Unread postAuthor: Ragnarok » Sun Aug 17, 2008 7:03 pm

Mr.Sandman wrote:mcmaster? not surewhat is in the uk

There's no direct equivalent in the UK.

Personally, I tend to scrounge part lists from a mix of companies and stores like Airlines Pneumatics; BES; Screwfix; Direct Plastics Online; and a few local shops.

DYI wrote:Also, how is using Joules when talking about the kinetic energy of the projectile fired from a rifle inaccurate?

I what I meant was people talking about the power of their rifles in Joules/ft-lbs.
Power (being energy per unit time) is completely the wrong term to use,and not actually that much use in terms of launchers or firearms. If I said the power HEAL provides is around 40 horsepower, you'd look at me as if I was something the cat had sicked up - the number is useless.

I know I use the term myself sometimes, but...
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: CasinoVanart » Sun Aug 17, 2008 9:15 pm

Ragnarok wrote: If I said the power HEAL provides is around 40 horsepower, you'd look at me as if I was something the cat had sicked up .


I personally would not look at you that way, i would suggest the use of a Turbo or Supercharger to up those ponies. :roll: :D
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Unread postAuthor: Stifler69 » Sun Aug 17, 2008 11:17 pm

I'm a little bit sick at the moment so yeah ...
Well at the moment I'm trying to assemble a steel golf ball gun, although its taken me ages to find all the bits and peices i should have it complete soon.
It's quite a heavy a pneumatic so I'll probably have to make a turret or a durable stand for it.
I've just bought a 1 x 1" Modified Sprinkler Valve from BCARMS (helping to do my part lol) and should be installing that this weekend.

I've based the design on a sniper rifle that i saw on the internet....
Hopefully all goes well and you'll all be able to see it really soon, I'm so excited to see what happens lol
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Unread postAuthor: Ragnarok » Mon Aug 18, 2008 10:11 am

CasinoVanart wrote:I personally would not look at you that way, i would suggest the use of a Turbo or Supercharger to up those ponies.

Right... well, when I work out how to get past turbo lag, I'll get back to you. :roll:

To say the number is useless is actually wrong - it needs processing, but I reckon it can be useful in it's own way.
I've had a theory for a while that a launcher's power is naturally more consistent than it's muzzle energy across a different projectile weights.

To take some numbers from GGDT for HEAL, and with an average acceleration power calculated from that:

<table border="1"><tr><td>Mass (g)</td><td>Muzzle velocity (m/s)</td><td>Muzzle energy (J)</td><td>Power (W)</td></tr><tr><td>5</td><td>301.6</td><td>227.4</td><td>28577.4</td></tr><tr><td>10</td><td>248</td><td>307.5</td><td>31777.0</td></tr><tr><td>15</td><td>217</td><td>353.1</td><td>31932.2</td></tr><tr><td>20</td><td>196.1</td><td>384.5</td><td>31421.1</td></tr><tr><td>25</td><td>180.3</td><td>406.3</td><td>30527.1</td></tr><tr><td>30</td><td>168.1</td><td>423.8</td><td>29688.1</td></tr><tr><td>35</td><td>158.1</td><td>437.4</td><td>28815.2</td></tr><tr><td>40</td><td>149.7</td><td>448.2</td><td>27956.5</td></tr><tr><td>45</td><td>142.5</td><td>456.8</td><td>27127.8</td></tr><tr><td>50</td><td>136.3</td><td>464.4</td><td>26376.4</td></tr><tr><td>55</td><td>130.9</td><td>471.2</td><td>25700.4</td></tr><tr><td>60</td><td>126</td><td>476.2</td><td>25004.7</td></tr><tr><td>65</td><td>121.7</td><td>481.3</td><td>24408.6</td></tr><tr><td>70</td><td>117.8</td><td>485.6</td><td>23839.2</td></tr><tr><td>75</td><td>114.2</td><td>489.0</td><td>23271.1</td></tr><tr><td>80</td><td>111</td><td>492.8</td><td>22793.8</td></tr><tr><td>85</td><td>108</td><td>495.7</td><td>22307.4</td></tr><tr><td>90</td><td>105.2</td><td>498.0</td><td>21829.7</td></tr><tr><td>95</td><td>102.7</td><td>500.9</td><td>21438.4</td></tr><tr><td>100</td><td>100.3</td><td>503.0</td><td>21021.3</td></tr></table>

In general, you'll note that muzzle energy tends to rise with weight, and the power tails off, although not by quite such a drastic degree.
(You might also notice that the 5 gram power figure sits low of the general curve, mostly because the velocity is entering the transonic range).

Taking just an average of the power from 10 to 50 grams in weight: 29500 W, I can work back from there and get a decent match to the GGDT velocity figure (to within about 6 m/s or ~20 fps) for any projectile in that mass range.

Try the same with the KE, and the 10 gram figure is nearly 40 m/s out - because the power is a more level and consistent figure.

Now because KE (proportional to the square of velocity) rises with projectile mass, and power (proportional to the cube of velocity) falls, it makes sense that there's a compromise to an order between 2 and 3 that has a very level curve.

Now, looking it over, it seems that compromise is pretty much exactly 2.5
Outside of the transonic range, the figure Mass * velocity<sup>2.5</sup> is surprisingly consistent across very wide ranges of projectile masses.

Figuring an average of 10,560 (using kilos and m/s) for this figure (between 10 and 100 grams) for HEAL at 21 bar, it's possible to predict GGDT's result to within 3 m/s (~10 fps) for most projectile masses, with a slight 9 m/s blip at the 10 gram end.

Knowing this is not necessarily very useful if you've got GGDT around, but it could be prove very useful for trajectory analysis (working out how range would be affected by a change of projectile mass) and predictions based on real world data, saving the requirement to test quite as many different projectile masses to generate a reasonably full and accurate set of data.

I need to finish all the stuff to go with the theory, but I'm hoping the observation could prove useful when calibrating my dart project, to help filter out the changes in muzzle velocity caused by small differences in projectile mass to help improve accuracy - because the results predicted from an average taken over over a mass range of fractions of grams and within that range should be very good.
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 31, 2008 11:51 pm

I just gave my latest project a quick low pressure test before heading to work, it fired woo! more details and hopefully 400 psi or so damage videos to follow later today :)
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Unread postAuthor: MrCrowley » Sun Aug 31, 2008 11:57 pm

jackssmirkingrevenge wrote:it fired woo!

Hmm...something's not right

:D
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Unread postAuthor: Ragnarok » Mon Sep 01, 2008 8:51 am

MrCrowley wrote:Hmm...something's not right

Wait, I think the universe is tearing apart, there's some kind of paradoxxxxxxxxxxxx

So this how the world ends. Not with a whimper, but an unexpected bang from one of JSR's creations. :p
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Unread postAuthor: frankrede » Mon Sep 01, 2008 12:41 pm

I'm still waiting on my piston valve:/
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Current project: Afghanistan deployment
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Unread postAuthor: jackssmirkingrevenge » Mon Sep 01, 2008 1:24 pm

MrCrowley wrote:
jackssmirkingrevenge wrote:it fired woo!

Hmm...something's not right


One of the harbingers of the apocalypse eh?

wanker.

:D

proof that this isn't a joke, including videos if I gather enough targets, to follow shortly ;)
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Unread postAuthor: Sticky_Tape » Mon Sep 01, 2008 2:12 pm

is it large or small cal.?
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: jackssmirkingrevenge » Mon Sep 01, 2008 2:37 pm

Sticky_Tape wrote:is it large or small cal.?


6mm, have a look here ;)
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Unread postAuthor: Brian the brain » Mon Sep 01, 2008 2:52 pm

ITWOST I shot a vid of the full auto snap thingy in action...

and am still waiting for it to be processed by youtube so I can show it off...
*EDIT* There is is!!

http://nl.youtube.com/watch?v=iq4loVzocHs
50 psi test


@ JSR, that thing looks so typically like.....one of your creations.

If I had to pick it out of a thousand cannons, just by looking at the picture's , there would be no doubt in my mind that this one is yours.

Nobody makes ém like you do.
Without the use for fittings they are always clean.

Now for a trigger and some paint.
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Unread postAuthor: frankrede » Tue Sep 02, 2008 6:01 pm

ITWOST
My mauler cannon is complete!
IT ROCKS
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Unread postAuthor: Sticky_Tape » Tue Sep 02, 2008 6:30 pm

I made a 6mm blow forward breech for the frig of it. Works good but I don't think I will be useing it on a gun any time soon
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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