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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: LeMaudit » Thu Apr 07, 2011 8:12 am

Nice photographs! NZ is such a beautiful country.

i still think the dye idea would work well,

Me too :) . But this will be for the next version, let's keep it simple for a first try.

There is just no way an LED will help track the projectile in flight and I worry if smoke would even be visible after 2000m.

Me too . :D I really thing smoke would just dissipate too quickly. It might give a good clue for the precise direction, and maybe an idea of the impact point for a short while, tracking it with some strong binoculars.


I've open the alarm, I was hoping that the internal would be a narrow circuit board with everything attached to it, but no luck. The piezo are 20mm diameter which would need a minimum diameter 1" (25mm) to accommodate them. And the resonance chamber is part of the plastic casing. That plus the fact the piezo might not survive the Gs as previously stated, I don't think it worth the try for now.

I have redesigned the missile to keep it around 20mm diameter, and simplified a bit the machining operations. Things will be kept together by a threaded rod (brass or steel), with a large nut/spacer in the middle to be able to make 2 adjustable chambers. The front for some weight, the back for whatever you like ;-) I'll drill small holes around at an angle for possible oxygen intake/exhaust so the drag should be minimum.

Unless someone share some better idea, I hope this weekend I'll make some metal chips :D
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Unread postAuthor: jackssmirkingrevenge » Thu Apr 07, 2011 8:34 am

MrCrowley wrote:Not sure how big of a difference 0.02± for a Cd is (would it be noticeable if a projectile's Cd was changed by ±0.02) but with a 20mm diameter, 100g projectile at a muzzle velocity of 360ms, a Cd of 0.1 ±0.02 can equal 1000m difference in distance. Is there an easy way to calculate a projectile's Cd value (from what I recall, there isn't)?


Does your student budget stretch to making a small wind tunnel ;)

I also thought about a projectile that would deform on impact to prevent deep penetration or one that broke in half.


I think a simple push fit would work brilliantly. It needs to have enough friction to keep the tail from coming off while travelling through the air, yet be loose enough to separate once the fins enter the ground.

If would also be possibe to say have the tail spring loaded and held by a pin that would dislodge on impact, or with some sort of pyrotechnic element replacing the spring. This would also work great for a radio transmitter, a long aerial could be coiled inside the projectile body and they unfurl as the transmitter is flung out.

edit: This is reminding vaguely of theADSID sensors which the Americans dropped along the Ho Chi Minh trail during the Vietnam war to detect troop and vehicle movements, which were designed to bury themselves leaving only an antenna visible that was disguised as a small plant.
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Unread postAuthor: POLAND_SPUD » Thu Apr 07, 2011 1:51 pm

yeah, that's what I wanted :-D

ohh check it -> http://www.grc.nasa.gov/WWW/K-12/rocket/rktsim.html
probably not very accurate as far as cd value is concerned but it's still fun to use
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Unread postAuthor: POLAND_SPUD » Sat Apr 09, 2011 3:21 pm

sorry for double posting.... but don't you think it would be a good idea to slow down the projectile in the final phase of its flight?

a simple time delay mechanism that triggers deployment of a parachute is definitely within our reach


if you think of it there are other possibilities... with a drag stabilised projectile the exact moment of deployment could be trigggered by a tilt sensor
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Unread postAuthor: LeMaudit » Sat Apr 09, 2011 4:53 pm

a simple time delay mechanism that triggers deployment of a parachute is definitely within our reach


I dare you to design something that will fit inside a 18mm body :lol:
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Unread postAuthor: POLAND_SPUD » Sat Apr 09, 2011 5:17 pm

I was actually reffering to MrCrowley's gun...

I wonder how difficult would it be to build a system that relies on a heater wire wrapped around a thin string and a simple switch that closes the circuit as soon as the projectile leaves the barrel

exact timing would probably be an issue... though I am sure that his round could accommodate a more elaborate mechanism (555 timer ?)
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Unread postAuthor: LeMaudit » Sat Apr 09, 2011 5:28 pm

Well, the 18mm ammo is for MrCrowley's gun :D I'll make a sabot too ;-) And he will fire it, not me. I'm more in the 50 cal myself, and already have some silly plans in mind... BTB old Old Shatterhand look and style always bugged me! :twisted:

The idea was to make an ammo small, heavy and aerodynamic to reach maximum range. After filling my MiniBoy with pieces of tungsten... not sure if there will be any room left. If you plan for a bigger ammo... then what about the small and heavy idea for a better range?
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Unread postAuthor: POLAND_SPUD » Sat Apr 09, 2011 5:39 pm

I'm more in the 50 cal myself
Yeah, me too

and yeah, I know you want to maximise range...
but is it really taht important if you can't find the projectile afterwards ??

For me it would be great if he really sent some payload downrange
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Unread postAuthor: LeMaudit » Sat Apr 09, 2011 5:48 pm

but is it really taht important if you can't find the projectile afterwards ??


Well, that was the first idea from this thread... how to find it :D

But now that I'm making a shiny missile... I wonder if MrCrowley will have the guts to fire it and possibly (most certainly) lost it... maybe he'll just pretend and keep it for himself :lol:
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Unread postAuthor: MrCrowley » Sat Apr 09, 2011 6:09 pm

LeMaudit wrote:But now that I'm making a shiny missile... I wonder if MrCrowley will have the guts to fire it and possibly (most certainly) lost it... maybe he'll just pretend and keep it for himself :lol:

Oh I'll fire it alright :D

If we can't find a solution for locating the projectile I'll shoot it and spend 15min looking around in case I get lucky.

@POLAND,

The main reason I want to find the projectile is to confirm the range.
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Unread postAuthor: POLAND_SPUD » Sat Apr 09, 2011 11:13 pm

lol finding that
miniboy4.png

Might be a little bit more difficult than you expect...

Once I shot 40 cm long rebars... never found them afterwards, which is kind of strange considering that the range was around 120 meters :D
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 11, 2011 12:31 am

POLAND_SPUD wrote:a simple time delay mechanism that triggers deployment of a parachute is definitely within our reach


Interesting thoughts, personally I don't think a parachute is a good idea as it exacerbates the wind drift variable and impact point would not reflect the true range of the projectile. Also, it wouldn't make the thing any easier to see.

I do however think that a spring loaded mechanism triggered by impact would be beneficial, separating the tail unit preventing it from being buried in the ground. I'd love to draw some diagrams but access is fairly limited at the moment.
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Unread postAuthor: jor2daje » Tue Apr 12, 2011 9:58 pm

after the disappointment of my last all steel projectile (the black and white striped one) I decided to try and make a similar shape but that is made more like the actual bomb it was based of, as I believe JSR said the real one was made with a steel tip and an aluminum body so thats what I did, two pieces that thread easily together. This is hopefully just a proof of concept that I threw together this afternoon but if it works I will make a more refined tip and several replacement tails as I think those are the things likely to break in an impact. I still need to make a more effective sabot than my last one so any suggestions would be appreciated I think ill make one out of wood for my first firing. Havent test fired it yet but based on throwing it around I have pretty high expectations.

the whole thing with a quarter for size (the tail will taper more uniformly on the final version, I drilled my hole for the tap a little too deep).
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shows the center of gravity, seems acceptable but could be improved on, the steel male threaded portion although hollowed out is still a little on the long side, and the tip could be larger and better shaped
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Unread postAuthor: MrCrowley » Tue Apr 12, 2011 11:30 pm

Going back to tracking/finding devices, what about putting a 50mW laser inside the projectile :D :D

Would look awesome, probably wouldn't help much though :(


Edit: Got some input from D_Hall, he mentioned glow in the dark dye which is something I don't think we considered. With virtually no light pollution on the beach at night, it could very well be effective in even small quantities.
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Last edited by MrCrowley on Wed Apr 13, 2011 12:03 am, edited 1 time in total.
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Unread postAuthor: Technician1002 » Tue Apr 12, 2011 11:57 pm

With the forward CG and looking at typical ordinance profiles, you may be able to trim back the fins a lot for lower wind resistance. Model rocketry has smaller fin to body ratio then that has. Are you considering trimming the fins?
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