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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: Hotwired » Sat Apr 02, 2011 10:37 pm

LeMaudit wrote:more like $100 for a tracking beacon!

http://www.gizmag.com/go/6499/
http://www.loc8tor.co.uk/Store/catalog/Products,110.aspx

That's a fun gizmo!
Maybe they are cheap as dirt in NZ? :lol:

[edit] thinking of it... if you have a iPhone you can use it as a projectile then track it on the web :lol:


you can expect up to 183m / 600 ft range. On the ground, and in corn fields this range will be reduced.


I'm thinking more of tracking beacons with a range of miles :P
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Unread postAuthor: MrCrowley » Sat Apr 02, 2011 10:44 pm

However you do it, still a long way to walk to pick it up again.

:D
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On tracking beacons, would they survive the launch? IIRC, Rag seemed to think electronics could have a problem with the Gs.
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Unread postAuthor: LeMaudit » Sat Apr 02, 2011 10:44 pm

sure... well... you can guesstimate the impact point... and search from there :-D a 200m radius is not that bad... 100m after another, you should find it. Maybe.

No idea really if they would survive the impact of the Gs though... :(
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Unread postAuthor: Hotwired » Sat Apr 02, 2011 11:14 pm

MrCrowley wrote:On tracking beacons, would they survive the launch?


This is one of those string questions. It might break on firing or maybe if you secured and padded it well enough it would be fine. Some types weigh considerably more than others among other differences.

Ones I'm looking at weigh from 3.5 to 9 grams (and cost £100-200).

Also, how it would be able to transmit is another question.

Despite being at the worst point regarding pressure I think a tail mounting would be best. Dart would be likely to skewer the ground on impact and leave the tail sticking up. A decent sabot could protect it enough for the launch.
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 03, 2011 1:18 am

In summary, a "teardrop" shaped full bore projectile would perform well, but clearly not as well as a saboted dart.

In this regard, Fnord's suggestion of using tungsten electrodes is a good one, as they are about as dense as you can get and not too expensive, however a simple rod with fins added would be simply too good a penetrator and likely bury itself completely in the ground, especially if it hits soft sand, and as such would be impossible to locate. A beacon could not fit aerodynamically either, so some sort of compromise is needed.

I'm thinking of something like the diagram attached, as to tracking beacons there are resources to make your own (assuming the light/acoustic beacon is unsuitable) and a GPS tracker (requiring a SIM card but nothing else) can be purchased for less than $75 though it would be a little bulky. Good instructable article for a radio beacon here.

I would advocate full bore fins, each with two contact points in the barrel to ensure stability without too much friction, because it would allow the sabot to be a simple cylinder that doesn't need to be too elaborate.

The beacon would be placed between layers of foam or any similar damping material to reduce the shock of firing and impact.
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Unread postAuthor: MrCrowley » Sun Apr 03, 2011 1:28 am

Think I should rule out the beacon here and now if homemade versions cost ~$75. I am a poor student after all :P
Smoke is looking like the most likely choice for this. Depending on the diameter of the rod, one could drill a cavity in to the tail section and stuff it with smoke powder and steel wool.

Would you recommend the full bore fins to stop the projectile tunneling its way New Caledonia? To 'control' the distance and tunneling effect of the projectile, a tall boy design could work well. I don't mind shooting for maximum distance, after all it is LeMaudit's projectile, but I wouldn't hedge bets on finding a projectile further out than 2km.

Can some smart people weigh in on the likely hood of a TallBoy shaped projectile making it as far as 2km?
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Unread postAuthor: Technician1002 » Sun Apr 03, 2011 1:44 am

At night I have had good sucess in launching small LED flashlights. With a couple of spotters, quick triangulation on it's landing is possible. They survive launch OK. The landings tend to bust them much like my launched cans of soda pop.

A bright flashlight tumbling end over end in the night sky is a sight to behold. After launching a barrel full of glow sticks, the launch of the flashlight was the signal for the kids to grab glowsticks and the flashlight if they found it. It broke on landing so it was found the following day.

The flashlight landed lens first, so the battery pack tried to go through the front of the flashlight on landing.
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 03, 2011 2:02 am

MrCrowley wrote:Would you recommend the full bore fins to stop the projectile tunneling its way New Caledonia? To 'control' the distance and tunneling effect of the projectile, a tall boy design could work well. I don't mind shooting for maximum distance, after all it is LeMaudit's projectile, but I wouldn't hedge bets on finding a projectile further out than 2km.


The fins would have to be of thin profile and aerodynamically shaped, they would either penetrate too or shear off depending on the impact ground.

Can some smart people weigh in on the likely hood of a TallBoy shaped projectile making it as far as 2km?


Assuming a muzzle velocity of 700 feet per second, this is what GGDT predicted for a 100 gram 42.3mm diameter projectile with a drag coefficient of 0.1, just under 1.5km.
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Unread postAuthor: MrCrowley » Sun Apr 03, 2011 2:05 am

Hmm yes, we want that Cd halved! :D
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 03, 2011 2:19 am

Halving the C<sub>D</sub> (0.05) gives 2049 metres.

Increasing muzzle velocity to 1000 feet per second gives a range of 1830 metres for C<sub>D</sub> 0.1 and 2840 metres for C<sub>D</sub> 0.05

Increasing the weight to 150 grams and keeping a velocity of 700 feet per second gives a range of 1763 metres for C<sub>D</sub> 0.1 and 2452 metres for C<sub>D</sub> 0.05, showing the importance of sectional density.

I think the LED suggestion is a cheap and simple solution, you can get a 5 LED flashlight for $0.99 posted - I wouldn't condone night firing for safety reasons though.

In order to avoid a pyrotechnic element, adding a breakable glass portion filled with fine powder could also prove adequate.
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Unread postAuthor: MrCrowley » Sun Apr 03, 2011 2:28 am

Theoretically I can do 1000fps muzzle velocity with 100g.

I think the LED suggestion is a cheap and simple solution

Personally I don't think it will work at all. I'm not going to be shooting at night, LED's might not even show the projectile during flight and even if they do it wont matter since I wont see it land. I'm hoping that the smoke idea will have smoke burning long enough for someone to get a general idea of where it is. Though it looks like a dart might be the most practical projectile and if that's the case there might not be room for LED's or smoke depending on the rod diameter... :?

Good thing winter is coming up, I don't want to start a forest fire :D
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 03, 2011 2:42 am

MrCrowley wrote:Theoretically I can do 1000fps muzzle velocity with 100g.


Upping the muzzle velocity to 1000 fps GGDt suggests 1809 metres for C<sub>D</sub> 0.1.

Again, to emphasise the importance and effect of sectional density, I kept the same weight (100g), velocity (1000 fps) and C<sub>D</sub> (0.1), but halved the projectile diameter to 20mm.

For these values, GGDT suggests a range of 4386 metres - almost 2 and half times the range, without having changed anything about the launcher. The GGDT model is not necessarily accurate but it gives you a good idea of the performance we're missing out on by not using optimised projectiles.

Tech's sabot experiments are a good illustration of the velocity and therefore range and penetration benefits of using sub-calibre projectiles.

A small design exercise, I ran some numbers for a 0.25" diameter dart weighing 100g (using a tungsten core it would be shorter than a foot) fired at a very feasible (using a sabot) 850 feet per second and with an achievable C<sub>D</sub> of 0.1, and GGDT suggested a range of no less than 6207 metres - over three and a half miles! Again, it's just a virtual model, but still a sign of what might be possible.
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Unread postAuthor: Technician1002 » Sun Apr 03, 2011 4:27 am

LED flashlights are quite bright and easy to see in their flight.

With just one observer, you have direction, but distance is hard to judge. With 3 widely spread observers all walking towards the impact point will converge on the landing site due to triangulation. It works well if you have a good general landing zone already selected.

A cheap LED flashlight launched at night is awsome. I'll have to enlist a video camera operator next time I do one this summer.
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Unread postAuthor: MrCrowley » Sun Apr 03, 2011 5:04 am

I think realistically we'd be lucky to fit two or three LED's in the rear of a projectile, perhaps even only one if the dart body is 20mm in diameter. You'll still need a good sabot to protect it during launch.

With 3 widely spread observers all walking towards the impact point will converge on the landing site due to triangulation

"widely spread" in this case would mean three people along a 30m wide stretch of beach within a few hundred meters of me. I still don't think an LED would be bright enough, even with 35 seconds of hang time.

I remember I walked this stretch of beach with some mates last year and it was incredibly difficult to judge distance and landmarks. It's all very similar. As soon as someone takes their eye off the rough landing zone, we're going to be doing grid searches.

I would just prefer something that will give me the location of the projectile once it has landed. Using smoke still has a lot of problems I will need to figure out but I think it is a stronger idea than LEDs unless the LEDs stayed intact upon impact and the projectile didn't go underground.

Attached below is a photo of the beach (when I was there the tide was right in and measured roughly 30m wide), it will most likely look like this (weather wise) if I ever get around to shooting there.
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Unread postAuthor: Technician1002 » Sun Apr 03, 2011 5:19 am

I have sucessfully launched glow sticks and these LED Poi sticks at night. They are easy to track. A golf ball drilled with a glow stick crammed through it would be easy to watch at night. I launched a glow stick in an apple and lost it over the trees at the far end of the field one night. Due to a creek and thick underbrush past that, we did not find that one, but we know it cleared the trees on the way past the field.
http://www.scavengeinc.com/p-1436-led-lightstick-poi-stick.aspx
I tried to get a video of one of the night shots, but my camera is not sensitive enough for the shot. I do have video of walking to the landing site by going to where I saw it vanish and found it in tall grass at night.
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