Working designs for parachute ammo (with a difference...)

[homedepotpro]

when i put it into ggdt awhile back it said 140 g's i think, that a ballpark estimate.

[BigGrib]

what velocity is that and what psi and volume of air and blah blah blah cause all of those factors need to be taken into account right so how did you come up with 93 and 186 i mean aside from your hypothesised accelertation time and psi you dont know the barrel length and the mass of the golf ball and all that stuff

[paaiyan]

The mass and all that stuff doesn't really matter. The g-forces experienced are independent of mass, all that matters is the change in velocity and the amount of time that change took. 300 fps is about 91 meters per second. Divide that by the estimated .1 seconds for the time of acceleration and you get 914.6 meters per second squared. The gravitational constant is 9.8 meters per second squared. Divide your 914.6 by 9.8 and you have 93.3. That's 93.3 times the gravitational constant, the force of gravity. Technically you subtract 1 for vertical acceleration, and the calculations for horizontal are a bit more complex due to the not quite horizontal gravitational effect, but they yield nearly the same result anyway.

Side note, the record for g-forces survived by a human is approximately 180. That was only instantaneous though.

[Hubb]

Well, since the g-force will affect the camera, it would seem fair to say that one may need to figure some kind of way to eliminate / reduce the g-forces going up.

I'm not too sure on how to do this but some sort of cushioned sabot comes to mind, one that will break away when the camera reaches its maximum height and begins to come down.

[paaiyan]

Going up isn't the problem. Starting to go up is. Potato guns naturally have near instantaneous acceleration, there's nothing you can do about that.

[windshrike]

I say to start at minimal pressures(i.e. 5 psi) and work your way up until the camera no longer works. Of course, if you still want your camera after, make sure you stop when it still works but is going too fast to see easily.

About the parachutes: Test a few methods of folding them, but there is nothing foolproof.

[Ragnarok]

... Except very low pressures and a longer barrel.
Cameras like that aren't designed to stand more than light knocks, a few G at most, not several hundred. Most of the time the cameras are torn apart by the acceleration.
If you could get all parts accelerating at precisely the same rate, then it would be fine, but a spudgun can't do that.
If you could create a stable gravity pulse with positive feedback shielding, then it would be a pittance, but even I'm having trouble with that one. The rotating superconductors keep heating above their transition temperature, and it's all going wrong.

I still think just putting the camera on the RC heli is the best move.

P.S: I get about 2000 G peak acceleration for a golf ball at 100 psi.
0.1 seconds is a very long time for anything to be in the barrel.
0.01s to 0.02s is more likely.

[paaiyan]

P.S: I get about 2000 G peak acceleration for a golf ball at 100 psi.
0.1 seconds is a very long time for anything to be in the barrel.
0.01s to 0.02s is more likely.

Hey, if you think your time for acceleration is more accurate, have at it man. I was guesstimating, and made no assertions of fact.

[windshrike]

I just thought of something: make this parachute round, but rig the RC helicopter to drop it in mid-air. That would make a nice video.

[BigGrib]

ok so the barrel length is 36" to mid-diameter and the ball will be traveling at a blazing 300 fps, which means that ball will exit the barrel at full velocity @ .01 seconds, do all the math on that sucker and you get exatctly 928.57 G's bingo slam dunk yahtzee, thank you and goodnight

[jackssmirkingrevenge]

There's a few good ideas on this thread - I also liked this idea by dewey-1 which he claims functioned reliably:



Looking at the camera system, it looks like it could easily shed a few grams - shorted the wire and hook up the battery directly without a connector, strip the metal casing of the 9 volt etc.

Make sure the camera is well packed to be able to resist the acceleration forces, perhaps mounting it on a spring-loaded base would be a good idea.

[Carlman]

WOW!, thts alot of replies for a short amount of time lol

it kinda went off topic thn righted itself again so its all good

anyway, ive been searchin on the net and contemplating a few ideas, nd thnx go out to JSR for directing me to that other thread.

thnx for all the replies guyz, i WILL make this work...

[BigGrib]

actually we were figuring out how much g forces you need to make your camera rig be able to withstand, you should absolutely mount the camera on some sort of slide mount with a nice stiff spring backing it up, and if you were good with micro electronics so you have a gravity switch that when it starts to decend it triggers a co2 cartridge or some sort of charge to blow the chute, i relly dont think weight would be too much of an issue as long as you dont go hog ass wild with it, heck you coud run the gravity switch off the 9v running your camera.

[BigGrib]

here's another idea, if you were to take a model rocket and make it a nice fit in your barrel, maybe with fold out fins once it comes out of the barrel, and have your camera mounted in the nose cone and run your ignitor wire up and out the barrel, oh i forgot to mention you will need a combustion with at least a chamber fan in it, but use that model rocket to ignite the propane in your chamber to give it that kick out of the barrel before the model rocket fully ignites. there ya go

[Hubb]

Make sure the camera is well packed to be able to resist the acceleration forces, perhaps mounting it on a spring-loaded base would be a good idea.

That's what I meant in my above thread.