long range ammo MiniBoy Mark I

[saefroch]

Ah yes, the freefall problem... as mentioned above. I think personally that if Crowley can just find a highly reliable way to trigger the cake, or more simply a circuit, on an acceleration in the negative x direction (assuming that the initial acceleration is in the positive x), that'd be sufficient.

[ramses]

The mini boy experiences 9.8m/s^2, but so do all the components of the tilt switch. It is, effectively, in a weightless enviroment.

This is why people experience weightlessness in orbit; they are not away from gravity, they're just in continuous free-fall. The Mini-boy, is, in essence, orbiting the earth for a brief period of time. It's orbit intersects with the earth, though

[al-xg]

Yes but free fall is FREE of other forces. In air that pretty difficult unless you are going slow enough or are streamlined enough to make those forces negligible.

The lack of deceleration is what would have to be measured, it only gets weaker as the projectile slows and as gravity begins to help on the way down (the resultant force does any way).

Well that is, if you want something triggered before impact.

It sounds a lot better when shooting a spud gun becomes putting an object into orbit

Trigger on impact is good unless the projectile get buried too deep.
Shoot sand bags as a test ? Box-o-truth style just bigger.

Not very practical shooting at night but I think it would be very cool to use a powerful laser as a tracer beam from the rear of the projectile
Mmmm, even size wise this isn't practical but it would be amazing.

[Ragnarok]

...are streamlined enough to make those forces negligible

We're talking about a heavy, dense, pointy and stabilised projectile. It probably has a terminal velocity most of the way to the sound barrier.

It would have to be going pretty fast for drag to be enough to activate the sensor, and would be insensitive to the direction of "up" (as it is in fall) - so, if it goes off at all, it means it'd go off shortly after launch (as the water rocket video says), given that's when it'll be moving fastest.

Useless for detecting apogee, only really useful for detecting launch - and that's only if you are very careful about how you load it to stop it going off as you do.

[MrCrowley]

Not very practical shooting at night but I think it would be very cool to use a powerful laser as a tracer beam from the rear of the projectile
Mmmm, even size wise this isn't practical but it would be amazing.

Could land me in hot water. The beach is within 100km of Auckland International Airport and would be close to the flight paths for Fiji-and-Japan-bound planes.

I'm liking this discussion, lots of input from many members. The success of this launch doesn't rely solely on Le Maudit's projectile and my cannon

[ramses]

Not very practical shooting at night but I think it would be very cool to use a powerful laser as a tracer beam from the rear of the projectile
Mmmm, even size wise this isn't practical but it would be amazing.

Could land me in hot water. The beach is within 100km of Auckland International Airport and would be close to the flight paths for Fiji-and-Japan-bound planes.

I'm liking this discussion, lots of input from many members. The success of this launch doesn't rely solely on Le Maudit's projectile and my cannon

Shoot with your back away from the airport.

I think some testing is in order. Go to the beach with some high sectional density projectiles. Put 000 steel inside something like a soup can. If this works (and it probably will), you need to modify the sabot so the steel wool is exposed to the combustion gasses.

Having the steel wool on the back would create excessive drag, but if you used it to ignite visco, it could be discarded with the sabot and you would have a time delay, and then some flare comp inside the round.

[al-xg]

as the water rocket video says

that's because it is a rocket and is still accelerating, I know you know that but in this case it isn't really a good example. I have the feeling my post was maybe misinterpreted (probably not very clear ), I am talking about measuring the loss of deceleration.

I'm pretty sure there would be a measurable difference between deceleration at muzzle exit and in the flight past the apogee.

The merit of this discussion is I guess to point out that it is to theoretical, I doubt anyone is going to get around to calibrating what basically is a home made accelerometer.

A timed trigger would certainly be simpler in my opinion. The only real point in triggering is to insure that enough smoke or whatever it is is produced to be visible for long enough after the shot, otherwise it could be set off on leaving the barrel ?

I have the feeling this has been mentioned before, but how about making some castings from Miniboy, Epoxy and lead for example to be able to make some calibration shots ?

[Insomniac]

Yes, the water rockets are rockets, BUT they have a fairly short duration of thrust. Neglect that part of the flight, and you have very similar situation to the miniboy. However the water rockets are quite draggy while the miniboy is not, meaning the mercury switch has even less of a chance of activating in flight for the miniboy. In my mind this is good, however... It will leave the most likely point of activation at impact, removing the chance of the cake upsetting the flight.

Another thing to note is that even given a smoke trail in flight, it's going to be very, VERY difficult to pin down where it lands. I've crashed RC planes in fields before, and not moved my eye from the point of impact... yet still had to search for ten minutes to find it. Smoke upon landing would probably be better, provided someone can get to the expected impact zone quickly enough.

Another thought... MrCrowley, do you know any experienced RC hobbyists? Do you know anyone with a GoPro or similar lightweight, HD camera? A reasonably high altitude aircraft with a wide angle HD camera could capture a large area, perhaps a kilometer squared, with probably a good enough resolution to detect any sizeable smoke cloud... Comparing this with google maps for better resolution could really narrow down the search area, and if it doesn't prove useful it shouldn't jeopardize any other aspect of the experiment.


Also, @al-xg... The forces on the projectile due to gravity are identical at the muzzle, at apogee and at the moment before impact. The ONLY differences are due to air resistance. These are that at the beginning of the flight, the velocity and thus the drag will be higher, meaning the deceleration will be stronger. As the projectile slows, the deceleration will ease off. Finally, when terminal velocity is reached the force the interals will 'feel' will be 1G as the body of the projectile is no longer accelerating.

[MrCrowley]

Another thing to note is that even given a smoke trail in flight, it's going to be very, VERY difficult to pin down where it lands. I've crashed RC planes in fields before, and not moved my eye from the point of impact... yet still had to search for ten minutes to find it. Smoke upon landing would probably be better, provided someone can get to the expected impact zone quickly enough.

Another thought... MrCrowley, do you know any experienced RC hobbyists? Do you know anyone with a GoPro or similar lightweight, HD camera? A reasonably high altitude aircraft with a wide angle HD camera could capture a large area, perhaps a kilometer squared, with probably a good enough resolution to detect any sizeable smoke cloud... Comparing this with google maps for better resolution could really narrow down the search area, and if it doesn't prove useful it shouldn't jeopardize any other aspect of the experiment.

Ok so I'll concentrate my research on getting the MiniBoy to ignite upon impact and I'll try do some tests at the beach when I get the cake mix to see how well the smoke can travel through sand.

As for the RC thought, I don't know anyone who is in to RC let alone RC planes, unfortunately. Do you have any recommendations about a cheap and easy way to dye the smoke? I've read a little on the matter and it seems like you need a particular chemical.

Having the steel wool on the back would create excessive drag, but if you used it to ignite visco, it could be discarded with the sabot and you would have a time delay, and then some flare comp inside the round.

Think I mentioned before I couldn't get my hands on any visco in the foreseeable future although I probably can make some homemade if it comes to that. My plans for the steel wool was to have a little bit in each of the 6 holes with a little more at the base of the projectile by the holes, that way it wouldn't effect aerodynamics.

As a side note, I assume you guys are aware I can superglue MiniBoy together just before the launch so as to discard the internal bolt and create more room in the cavity.

A timed trigger would certainly be simpler in my opinion. The only real point in triggering is to insure that enough smoke or whatever it is is produced to be visible for long enough after the shot, otherwise it could be set off on leaving the barrel ?

I have the feeling this has been mentioned before, but how about making some castings from Miniboy, Epoxy and lead for example to be able to make some calibration shots ?

I do have a delrin/nylon/one-of-those-plastics 'practice' MiniBoy originally intended to test the sabot. Although I initially pushed aside the idea, recently I've been thinking about doing small scale tests at a local field with a pneumatic just to make sure the sabot is working well.

I'll talk to my dad about some triggering mechs, he might have a suggestion.

[Insomniac]

Not sure on how to colour the smoke, I really was never much of a cook so I have only very limited experience in baking cake.

And if you superglue it, be careful. Superglue can hold a lot of weight, yes, but it's an acrylic bond. It can crack quite easily and I'm not certain it would be up to the task of holding the MiniBoy together. You can get 90-second epoxy, though I'm not sure how long it takes to reach a useable strength.

[jackssmirkingrevenge]

I'm liking this discussion, lots of input from many members. The success of this launch doesn't rely solely on Le Maudit's projectile and my cannon

In other words, "If I screw this up, it's not just my fault"

Nice move, MrC

[Ragnarok]

I am talking about measuring the loss of deceleration. I'm pretty sure there would be a measurable difference between deceleration at muzzle exit and in the flight past the apogee.

Yes, if you could actually measure the deceleration from drag accurately, then most things would decelerate rapidly, reach their slowest deceleration at apogee, then start decelerating more rapidly as they picked up speed again.

However, that's a pretty subtle change to measure, and I expect any accelerometer accurate enough would get completely trashed by the thousands of G in the barrel.

[LeMaudit]

I'm liking this discussion, lots of input from many members. The success of this launch doesn't rely solely on Le Maudit's projectile and my cannon

In other words, "If I screw this up, it's not just my fault"

Nice move, MrC

Yes, that's quite nicely put. Smart guy...

[al-xg]

This is past the useful point for this topic but

The forces on the projectile due to gravity are identical

I'm not saying gravity stops. The components on each axis change with orientation, if you hold a mercury switch horizontally it does nothing, unless you move it from side to side and induce acceleration or deceleration.


Mmm, can't really remember the discussed values, but assuming 80g, 20mm projectile, 0.06Cd, 380m/s and a 41 degree launch angle, there should be about 1.2N difference in drag alone between barrel exit and just before impact. 11.76Kg

Could land me in hot water.

Haha, firing laser projectiles in orbit crossing flight paths with airliners. Excellent !
The whole pointing lasers into plane cockpits is only really an issue on take-off landing because of the distance and well the cockpit being on top. But I would hate to have to explain that to authorities having been caught with an supersonic laser bullet canon


Are industrial made smoke bombs generally better than the home made option ? I've seen orange smoke pellets used to test out chimney draught, i'm pretty sure they're not that expensive.

[ramses]

Colored smoke uses a dye, which would be a problem. If you're shooting this at night, keep in mind that the smoke will be hard to see. I'm thinking downrange observers and a "tracer" type projectile would be best.

Can anyone think of a good way to discharge glowstick juice on impact? It might be worth trying with something like a pop-can.

To replace the visco, you could use a "delay cake" (baking soda reduces burn rate)

If you wanted the smoke to come out during the day, ordinary cotton string burns very slowly. If you soaked some in nitrate, I'm sure it would burn a little more reliably and quickly.