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Mortar Explosions


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#1 Joseph Nesbitt

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Posted 01 October 2007 - 07:20 PM

I was watching this extra in the Band of Brothers dvd set which mentioned alot about how they did the effects, the most interesting was this giant fan looking thing that threw dirt in the sky when you pressed a button, they buried it in the ground to simulate mortar explosions. Is this something they made themselves, or something that you can purchase? Or is there a more practicle way to simulate the effect? Any advice will help.
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#2 Douglas Sunlin

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Posted 02 October 2007 - 11:21 AM

It's done with model rocket igniters (electrically triggered) and small bags of black powder or flash powder, with a pile of blackened cork on top. When this is lit off, it doesn't make a loud bang, so the sound of an explosion is laid over that.
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#3 David Mullen ASC

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Posted 02 October 2007 - 11:30 AM

Usually those "air mortars" involve compressed air, I thought.
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#4 Douglas Sunlin

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Posted 02 October 2007 - 12:52 PM

You mean no pyro at all? What's this world coming to? :)
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#5 Leo Anthony Vale

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Posted 02 October 2007 - 01:53 PM

You mean no pyro at all? What's this world coming to? :)


Strangely enough, John Wayne's 'The Alamo' used wooden cannons with gas cylinders!

http://widescreenmov...WSM02/alamo.htm
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#6 Phil Rhodes

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Posted 02 October 2007 - 02:46 PM

You could do worse than:

http://www.detfilmsh...losions_02.html

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#7 Toby L Edwards

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Posted 02 October 2007 - 06:36 PM

Usually those "air mortars" involve compressed air, I thought.


I have the box set and David is correct. They use air mortars and the flying chunks are foam. Excellent Movie by the way.
I think they used the same set up on Saving Private Ryan if memory serves.

Toby
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#8 James Steven Beverly

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Posted 03 October 2007 - 02:47 AM

Is there a significant difference between an air mortor and an air cannon?
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#9 Joseph Nesbitt

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Posted 03 October 2007 - 07:24 PM

definatly, try searching either on google and you'll get significant differnances, the air moratrs usually have lots of compressed air, usually a machine attached, the air cannons can often be these one time use spfx things to shoot out confeeti, or blood and guts for head shots if you want.
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#10 Joseph Nesbitt

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Posted 03 October 2007 - 07:26 PM

oh yeah and Doug although I think toby might be right, where did you hear about rocket igniters? I'd like to see that, any clips or movies where they use that for this purpose or possibly another
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#11 James Steven Beverly

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Posted 04 October 2007 - 02:43 AM

definatly, try searching either on google and you'll get significant differnances, the air moratrs usually have lots of compressed air, usually a machine attached, the air cannons can often be these one time use spfx things to shoot out confeeti, or blood and guts for head shots if you want.


Though, I like confetti, I was thinking Fullers Earth and painted Styrofoam chunks shot straight up out of a sawed off one with about 100 to 120 psi while either hidden in a depression, a hole or behind a bush, perhaps a pair used in tandem and set off at the same time to give a wider spread of dust and debris. That coupled with an electronic flash on the same circuit and possibly a sound effect in post would sell the effect. How would the blood and guts for head shots work, small one behind the actor aimed at the wall?

I've seen flash pots and concussion pots on stage shows I've done but never messed with them, THOSE are set off with some kind of electronic igniter, but I believe you need a pyro license to set them. I wonder if you set an amount of Fuller's Earth on top of a concussion pot charge if it would give you the desired effect?
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#12 Brad Grimmett

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Posted 04 October 2007 - 09:59 AM

Though, I like confetti, I was thinking Fullers Earth

From what I understand, Fullers Earth is very bad to breath. Every time I'm on a set that is using it I ask for a mask so that I don't breathe it in. But actors can't wear a mask, so be careful and aware about Fullers Earth when using it.
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#13 Douglas Sunlin

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Posted 04 October 2007 - 11:39 AM

oh yeah and Doug although I think toby might be right, where did you hear about rocket igniters? I'd like to see that, any clips or movies where they use that for this purpose or possibly another

I confess this is not an insider view. It's from various "Making Of" featurettes, notably one for Independence Day. It's an old technique, as far as I know; probably the pyrotechnics required extra insurance and a special technician.

Something like this:
http://library.think...cts/stunts.html
Except that they spell primer cord as prima cord. Maybe that's a trade name.
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#14 Dan Salzmann

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Posted 06 October 2007 - 03:14 AM

Are there any books that give detailed information on pyrotechnics for movies?
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#15 James Steven Beverly

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Posted 08 October 2007 - 02:36 AM

From what I understand, Fullers Earth is very bad to breath. Every time I'm on a set that is using it I ask for a mask so that I don't breathe it in. But actors can't wear a mask, so be careful and aware about Fullers Earth when using it.



Yeah, it's a pain in the ass to deal with but it works. It will get the effect you're looking for. I suppose it's better than using a bucket of dirt, which is a HELL of a lot cheaper. :D
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#16 James Steven Beverly

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Posted 08 October 2007 - 02:42 AM

Are there any books that give detailed information on pyrotechnics for movies?


There's a book called "Secrets of Hollywood Special Effects" by Robert F. Mc Carthy that has some stuff in it but I don't think learning Pryo from a book is a good idea unless you like the name "Lefty". :blink:
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#17 David Mullen ASC

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Posted 08 October 2007 - 10:24 AM

Often they use a mix of Fuller's Earth (or crushed walnut shells these days) and broken-up cork for the chunks that fly up.
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#18 James Steven Beverly

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Posted 10 October 2007 - 03:33 AM

Good to know. :)
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#19 Bob Hayes

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Posted 10 October 2007 - 12:14 PM

I think ?Wind Talkers? had some of the most amazing pyro. It looked like huge amounts of earth were lifted into the air. I heard the used a lot of high explosive to achieve that effect. The explosive they used was so unstable they had to keep it refrigerated until they used it. I?m curious as to what they used.
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#20 Greg Johnson

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Posted 15 October 2007 - 06:02 PM

I thought about getting one of these for my WWII short. Thunder Pipe.

I love how they demonstrate it with a massive fire ball in their drive way. I wonder what that dude's neighbors think.

We opted not to get that, and cut the scene. We ended up just throwing dirt clods near the actors,.. on set it was super lame,.. once I added sound it actually looked awesome.

- Greg
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