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long range ammo MiniBoy Mark I

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 06, 2011 11:35 pm

saefroch wrote:I think Rag pointed out... a tilt switch won't work since the miniboy's in freefall. No gravity = no tilt to sense.


The man does have a point. Hmmm...

POLAND_SPUD wrote:you should have chosen a design that is cheap and easy to produce


Hate to agree here but I feel the same way, LeMaudit simply made something that's too good to fire.

When they make jet engines for target drones or cruise missiles (like the J85 started out as), they only have to work once so they are built to a much lower specification with lower quality materials.

In the same way, I'm of the opinion it would have been much better to make a set of darts with full calibre fins as proposed a while ago:

Image

This simplifies the sabot to a basic disk and the projectile is just as aerodynamic, can use an existing tube as a body with plenty of space for 'lectrics or whatever recovery method is deemed suitable.
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Unread postAuthor: Insomniac » Fri Oct 07, 2011 12:18 am

To be honest, I prefer the idea of a purely ballistic projectile... No minimal thrust, no base-bleed... Just a well shaped dart being acted on by purely aerodynamic forces. I know no-one has the intention of turning the miniboy into a rocket, but all these discussions of cake being served mid-flight...

And just to hammer home the point about level switches:

[youtube]http://www.youtube.com/watch?v=JDWYTphuGCs[/youtube]

Could there exist a more appropriate video? :D
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Unread postAuthor: Crna Legija » Fri Oct 07, 2011 12:23 am

do you think the glass would take the Gs from the firing?
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 07, 2011 12:25 am

Insomniac wrote:To be honest, I prefer the idea of a purely ballistic projectile...


Likewise, after all that was the original point of this "challenge" in the first place ;)

Could there exist a more appropriate video? :D


:oops:

That's my idea shot down then... right, as you were.
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Unread postAuthor: MrCrowley » Fri Oct 07, 2011 12:26 am

saefroch wrote:No previous nozzle discussed, but it'd let you see the location if it's under sand, it'll blow the sand away. Really. Those gases are moving REALLY fast right near the nozzle. I suggest nozzle, which will add thrust and range probably.

That does seem like a good idea now that I've seen your video. I guess I'll add the nozzles inside the holes already drilled so as not to fućk up the aerodynamics.

saefroch wrote:I think you could fit a capacitor, a photoflash might even work, or smaller. Capacitors come in all sorts of sizes, I've no doubt you could fit one.
I'll have to do some research tonight then, I've pretty much avoided discussion about capacitors and know little about them. The triggering part is still difficult and accelerometers look too big and expensive (the premade circuits anyway).

Insomniac wrote:To be honest, I prefer the idea of a purely ballistic projectile... No minimal thrust, no base-bleed... Just a well shaped dart being acted on by purely aerodynamic forces. I know no-one has the intention of turning the miniboy into a rocket, but all these discussions of cake being served mid-flight...

I'd be happy to drop the idea of smoke tracking whether initiated in-flight or pre-flight as long as we can think of another tracking system that has half a chance at working.


Edit: I realise there is some what of a discrepancy between my first sentence and last sentence as I wrote this reply while you guys were adding more replies. Like you and JSR, I'd rather not have the smoke effect the flight of the projectile, I'd prefer al naturale :D
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 07, 2011 12:54 am

While a level switch may not detect apogee, it will certainly detect the sudden deceleration when the thing hits the ground.

If that starts some smoke going, surely it will seep through any loose sand that would fall into the hole made by the projectile?
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Unread postAuthor: MrCrowley » Fri Oct 07, 2011 1:29 am

True indeed! Perhaps I can do some testing at the beach.

The penetration of the Lazy Dog 'bombs' are a little unsettling , some go through as much as two feet of (I assumed packed) sand. MiniBoy will hit on a slight angle and I guess sand is fairly permeable anyway so hopefully enough smoke will make it through.
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Unread postAuthor: Insomniac » Fri Oct 07, 2011 1:43 am

Correct JSR, a level switch can still be a good idea because it will most definitely detect the impact. One thing to think about is that you might want to handle the projectile with gloves if you find it... the cake will probably break the tube and although it's only a little bit of mercury, it pays to be cautious.

As for actually serving the cake, I have an idea. A small model rocket ignitor would work to get things going. A mercury switch would easily handle the current while being very small and pretty tough, particularly if you potted it in epoxy. Finally, the best option I can think of to deliver high currents in a very small package while being guaranteed to hold its charge, is a LiPo cell.

They can be had very cheaply and very, VERY small..

A small jumper run to one of the holes on the miniboy could be used as an arming mechanism. The only other thing to note is that the lipo must be charged before use, they arrive with a partial 'storage charge'. Charging a 50mah LiPo cell could be problematic, as that requires a 0.05A charge current... Most chargers only allow you to go down to 1A. Of course, if you could fit a slighly larger cell of at least 100mah capacity, you won't have any trouble purchasing (or borrowing from an RC hobbyist) a cheap charger which can go down to the 0.1A required.


EDIT: Scratch some of what I just said... that tiny 50mah cell is rated at a 2C charge rate. That means any cheap charger that does 0.1A rates will be fine.
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Unread postAuthor: POLAND_SPUD » Fri Oct 07, 2011 6:55 am

can't you calculate the predicted time of flight and build a system that activates whatever you want to activate X seconds after leaving the muzzle ?
I guess a capacitor could be used to do that
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 07, 2011 7:15 am

POLAND_SPUD wrote:can't you calculate the predicted time of flight and build a system that activates whatever you want to activate X seconds after leaving the muzzle ?
I guess a capacitor could be used to do that


An impact switch can be built much simpler and more compact, leaving more room for cake mix.
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Unread postAuthor: POLAND_SPUD » Fri Oct 07, 2011 8:47 am

In the same way, I'm of the opinion it would have been much better to make a set of darts with full calibre fins as proposed a while ago
yup exactly... a pvc pipe, nose cone, perpendicular notches cut in the pipe for fins and simple fins
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Unread postAuthor: al-xg » Fri Oct 07, 2011 12:07 pm

Base bleed will only work if the projectile is supersonic, increasing the pressure behind the projectile at subsonic velocities will cause the boundary layer to shred earlier.

Ermm, doesn't that video show that the rocket ins't in in theoretical free fall, and that air drag is enough to counter the G's acting on the level switches ?

The problem here is really more stopping it from triggering too early as obviously deceleration starts as soon as the projectile leaves the bore.

He didn't mention what the differences between the mercury switches was though... More or less mercury ?

In parabolic flight, there might be a problem with not reaching a point of zero deceleration as the vector won't be vertical, they will always be a component affecting the projectile in the longitudinal axis.

For people in the UK,
http://www.bbc.co.uk/bang/ask_yan/zero_gravity
at kids science show :) pretty interesting topics though...
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Unread postAuthor: warhead052 » Fri Oct 07, 2011 1:32 pm

jackssmirkingrevenge wrote:
warhead052 wrote:...burning inside the miniboy. That way you get the cool steel wool effects that act like tracers without being incendiary


:wink:


What I meant was without the incendiary powder most tracers are coated with....
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Unread postAuthor: saefroch » Fri Oct 07, 2011 1:42 pm

al-xg wrote:In parabolic flight, there might be a problem with not reaching a point of zero deceleration as the vector won't be vertical, they will always be a component affecting the projectile in the longitudinal axis.
*facepalmheaddeskcombo*

The projectile experiences ~-9.8m/s<sup>2</sup> the moment it exits the barrel until it hits the sand.
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Unread postAuthor: al-xg » Fri Oct 07, 2011 2:36 pm

Unless the projectile is flying straight up or straight down only a component of that 9.81m/s^2 is acting in a useful way on the mobile part of a tilt switch set along the longitudinal axis of the projectile.

It also experiences 0.5*rho*A*V^2*Cx/m, and quite a deceleration on impact.
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