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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 » Tue Apr 05, 2011 10:33 pm

Sarcastic? me? :D

Just let's hope MrCrowley have a dog... and sausage meat...

now why did I just think about hot dogs!? Weird... :wink:

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Unread postAuthor: MrCrowley » Tue Apr 05, 2011 10:37 pm

Important: My barrel diameter is 48.5mm NOT 42.3mm!


Sorry, I f*cked up before :D


edit: The dog idea isn't actually that bad. I do have a dog, a 14 year old jack russell, he wouldn't be up to the task :wink:
My friend does have a much younger variant jack russell (or terrier) that could possibly be used but I wouldn't want to spend so much time training the dog haha.

Few more transmitter circuits:
http://www.sentex.net/~mec1995/circ/fmt1.htm
http://www.scribd.com/doc/128845/Electr ... er_page_40
http://www.scribd.com/doc/128845/Electr ... er_page_65

Anyway we could get around the antenna problem?

[edit 2]: Here's a pre-made FM transmitter boasting a range of up to 1km. Doesn't say how long the antenna is. Slight problem that it uses a microphone, perhaps there is a way that can be replaced with something which makes a tone?

[edit 3:] ...and another
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Unread postAuthor: Technician1002 » Wed Apr 06, 2011 1:56 am

The antenna problem is relatively easy to fix. A 1/4 wave antenna is inversly proportional to the operating frequency. US FM band is near 28 inches. 2 meter Amature radio is about 50cm.

When you get to a wireless camera such as an X10 product running in the 2.4 Ghz band or a 5.8 Ghz cordless phone, the antenna lengths are quite reasonable.

Some common frequencies and the 1/4 wave antenna lengths are below in metric for you.
29 Mhz - 2.459 M 10 meter Amature band
100 Mhz - 0.713 M FM Radio
460 Mhz - 0.155 M FRS Walkie talkies
2.4 GHZ - 0.030 M WiFi or cordless phone
5.8 Ghz - 0.012 M Cordless phone or G band wireless
10 Ghz - 0.071 M X band speed radar (baseball pitch speed radar)

A reasonable transmitter would be a wireless video camera and using a small dish antenna you could hone in on the direction of the signal.
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Unread postAuthor: MrCrowley » Wed Apr 06, 2011 2:55 am

Sorry Tech I don't really understand stuff like this that well so let me know where I've gone wrong in my understandings below.
Are you saying I need a transmitter from a wireless video camera or I need to change the frequency of an FM transmitter to one that only requires a short antenna length? I would also need a different device to hone in on the transmitter since it will broadcast outside of FM frequency?
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Unread postAuthor: Technician1002 » Wed Apr 06, 2011 3:33 am

It is a given that what ever frequency you transmit on you will need to be able to detect and hone it on it.

Instead of launching a laptop computer with WiFi on, a smaller solution is to launch something smaller in the same frequency band. The receiving antenna if placed in an old satelite dish can be used to sweep the horizon for the best signal to find the direction to go.

Lower frequencies require larger antanna arrays to direction find the source of a radio signal. The transmitter uses a larger antenna too.

FM radio can be used, but most consumers have no real easy way to tell what direction the signal is from. The result is often, I'm somewhere near the transmitter but where is it from here?

More info on finding hidden transmitters can be found by looking at Amatur Radio sites regarding "Bunny Hunts" or "Fox Hunts"
http://www.w7sky.org/rules.html
Unfortunately most portable FM radios do not have a good signal strength meter.
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Unread postAuthor: LeMaudit » Wed Apr 06, 2011 7:49 am

I don't understand much emitters/transmitters, but what we need is NOT something that give the direction, that we know very well, but the distance from the target. Only with a direction, triangulation is needed, right? Not that easy in a narrow band of land. :D

The RF solution is either expensive, or require an expert to help. Tech, would you like to join the project and make the RF part? :D I could prepare a shell with a given internal cavity size if we can plan it.

Without any quick and viable and cheap solution, I propose to go ahead with a shell as heavy as possible around 20mm diameter.

MrCrowley, if you have access to a grinder and some tungsten electrodes, you could give me a diameter for the cavity to be filled with a piece of electrode. Would save me some serious shipping cost :) CanadaPost is not cheap. And it would be a good way to make something small, sturdy and heavy.

As for the sabot, not problem to make a thick aluminum plug that diameter, but I might have problem finding the material for the two half cylindrical other parts.. maybe I'll use hard wood (maple) for that. Unless someone have another idea? for ready made materials, I only have access to imperial sizes here, no metric tubing.

[edit] Ive read grinding tungsten electrodes is dangerous, so please be careful if we follow that direction.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 06, 2011 8:39 am

I think direction is enough. If you can determine that the projectile in say a 3-4 metre band in front of you and you walk along it, you should find it (or a burrow leading to it :roll:) fairly quickly
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Unread postAuthor: LeMaudit » Wed Apr 06, 2011 9:14 am

I agree if a few metre narrow band is feasible.. but is it?
Is it really that precise!? :shock:
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Unread postAuthor: Ragnarok » Wed Apr 06, 2011 9:22 am

It works fine. Take GPS coordinates for your launch, head in the direction your tracker is giving, find projectile (it'll be when your tracker suddenly says its behind you), take GPS coordinates again. Work out difference.

Although, that said, sync up two triangulation points that will figure vertical angle as well, and you could you could actually track it in flight, recording height, distance and velocity for the whole trajectory.

Which would obviously be pretty awesome.
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Unread postAuthor: POLAND_SPUD » Wed Apr 06, 2011 12:42 pm

IDK why you really need anything more than a bright LED/ a few LEDs ?

Build a projectile that will embed itself in the ground....
launch it at dusk...
I am sure it will be a lot easier to find it at night
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Unread postAuthor: Ragnarok » Wed Apr 06, 2011 1:34 pm

POLAND_SPUD wrote:IDK why you really need anything more than a bright LED/ a few LEDs?

Because anything with the high sectional density and streamlined shape to go a couple of kilometres won't just "embed itself in the ground". It will embed itself underground.

And without line of sight, LEDs are useless.
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Unread postAuthor: POLAND_SPUD » Wed Apr 06, 2011 2:08 pm

to go a couple of kilometres
lol I think that it might be a good idea to start small... :wink:

It will embed itself underground
as above it is a problem for some designs... sure it's cool to talk about APFDS projectiles and >5km ranges but let's be sensible

and yeah I do realize that it can be a problem, but it's not that there is no way to keep the LEDs on the surface of the ground... or add a 2 metres lenght of optical fiber to the base of the projectile?
(even a transparent tube works great)
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Unread postAuthor: CpTn_lAw » Wed Apr 06, 2011 2:20 pm

It's a shame we are not allowed to talk about pyrotechnic mixtures, because some sort of impact sensitive cap + smoke generating mixture would be very convenient for recovering projectiles...
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Unread postAuthor: LeMaudit » Wed Apr 06, 2011 2:51 pm

POLAND_STUD... now you're talking sci-fi :D optical fiber, really :shock: I will be happy if the metal body it still in one piece, even with a more "gentle" impact in sand than hard soil.

It's a shame we are not allowed to talk about pyrotechnic mixtures


You just did it :lol:
I'm prepared to make a Mark I simple but aerodynamic missile (copying the bomb shape) and see if it can be found and more importantly if it dig itself strait (meaning it didn't tumble). If not, it'll be time for Mark II ;-)

Now I need MrCrowley to tell me if he can find those heavy welding rods cut to size locally. I need as a start the rod diameter, as the internal hole need to be drilled first (steps need to be done in a certain order while machining the aluminium rod). And I want to keep an aluminum wall as thick as possible to try to keep the missile in one piece. I could check myself at the store but I'm not certain the diameter is the same between countries and manufacturers.

As an alternative, it could be filled with lead too.

I'll also cut open the alarm and try to stuff it in the tail... unless an electronic Wizard step in and offer some help ;-)
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Unread postAuthor: Ragnarok » Wed Apr 06, 2011 3:18 pm

POLAND_SPUD wrote:sure it's cool to talk about APFDS projectiles and >5km ranges but let's be sensible

Um - the whole discussion is about highly aerodynamic projectiles, ranges measured in the kilometres and solutions to proving/validating such.

This isn't lawn darts - anything actually fast and aerodynamic enough to be worth discussing in this thread will not obligingly stick tail out of the ground.
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