fake explosions

[bob]

Okay so I'm going to try a different one here soon, I like the idea of the cement but it is kind of costly so I'm thinking I'll try using clay dust.

now if I use clay dust instead of peat moss in the pyramid the clay will weigh way more then the peat moss, and I intend on using a gallon or two more of clay then I used when I used peat moss.

I used 452 grams of bp with the peat moss so would 2 kg's be enough for the clay? And one more question can I use touch'n foam to make fake roots to put in the pyramid so when it goes off it looks like roots are flying out?

bob

[Bobosan]

Roots? Might just try some dark colored sisal or bale string in short lengths tied together in the middle.

 

Don't forget the whole shank roast and pieces for body parts. They used fresh meat in "Talvisota" which is a movie depicting the Winter War between the Finns and Russians. Very, very realistic looking explosions.

[bob]

yeah roots, cause I think if I really set off a bomb in a field a bunch of tree roots would go flying off (at least where I live).

I fail to see how you would be able to see bale string easily enough.

bob

[Arthur]

Methinks you try too hard! only the most HUGE explosions on film really last more than a couple of seconds. In real film terms that's 25 - 50 frames and more likely the effect will last 20 - 30 frames. Longer than that and it's either sequential explosions or slow motion explosions or an edit composite of several camera perspectives of the same explosion.

Lots of the classic cartoon film explosions were shot at 100FPS and shown at 25FPS so that a cup full of lighter fluid looked like a whole fuel dump exploding! (Think Gerry Anderson and Thunderbirds)

[bob]

Ok so I found a few bags of mortar mix, and since it doesn't look like the clay will be dry I'm thinking of using the little clay I do have (about 7 gallons) and peat moss, plus this mortar mix, do you think that I should use this mortar mix? Thanks in advance, bob

[yvariro]

I personnaly think that any dust can work,but pay attention to the ecollogy risks,

 

I saw a little clip of a Pyrotechnic and SFX school and theys use a V shape recipient for making their explosion,they put BP or HE in the bottom of the shape

 

Look at 1:26

 

 

here is another video, look at 2:45

 

 

 

They use Flour but you can use your mortar mix

 

 

The soil where I live is really non hydrophilic,so when it's dry,it'can form dust,One day Ive tried to screen this dry soil,and it worked really good,with a nice brownish color,but the effect is less persitent than any other dust like clay,flour...

[bob]

I set off another one yesterday.

I didn't use the mortar mix, what I used was 32 litres of clay (17 mesh and under). a bag of 2.2 cubic feet of peat moss; which is a little bite more then what I used in the last one I posted, four 500ml bags of gasoline, 500 grams of four mesh black powder, and sticky match and an ematch to light it.

Here are a few pictures of it (from different angles) I think it got over 20 feet high, I'm going to try to get a video of it up in the next couple of days.

What do you think?

bob

[Bobosan]

That one looks real good.

[bob]

My dad got a large steel cone (it's used for crushing gravel, but he is going to use it for a fire pit) it's 60 inches wide and 39 inches tall, 150 gallon volume.

And I want to use it for an explosion simulation, my questions are

• Is there anything wrong with using this cone?

• Is there a faster way to grind 150 gallons of clay then my 6.7 liter ball mill

• This cone has about 5.25 times more volume then my pyramid one, in which I used 500 grams of lift (I also want to use a larger amount of clay in comparison then the last one so would 3000 grams of bp work?

bob

 

[Bobosan]

Sounds like this cone is thick walled steel. Hauling it around and digging it in may become a chore.

 

Kitty litter for clay? A large highway pavement roller would crush a lot of clay fast.

 

The charges are getting really large for this project. Might split the cone.

Edited July 12, 2013 by Bobosan

[bob]

Sounds like this cone is thick walled steel. Hauling it around and digging it in may become a chore.

 

Kitty litter for clay? A large highway pavement roller would crush a lot of clay fast.

 

The charges are getting really large for this project. Might split the cone.

Digging the hole will not be fun for sure, however I plan on using it not fare from were it is now so moving it won't be that bad.

Kitty litter is just to expensive for my budget so I'm using a course clay from a hole I dug.

Hehe yeah a roller might work not to bad (although it might not get it as fine as I want)

I don't think it will split as it's 1.25 inch thick steel.

[bob]

Sorry about this post I was trying to get some stuff on here however it didn't work, and now it doesn't look like I can delete it.

bob

Edited July 19, 2013 by bob

[bob]

Ok I've been really busy here lately so I just got the bp granulated a few days ago. I had to use a different charcoal then I did with the other effects so I'm thinking of using about 3400 grams of bp, Now my question is what are the chances of this cone flying out of the ground when I shoot it off? The cone is not a complete cone as in the bottom has been cut off, so it's a cone with a 12 inch wide hole in the bottom. What kind of a bottom will I have to put on it so that it is safe? Thanks for all your help guys. Edited August 16, 2013 by bob

[Bobosan]

Keeping the BP above the hole might keep the undercutting to a minimum. Maybe place a round cast concrete stepping stone over the hole. Another thought is to stake it down on the top edge somehow.

[bob]

Would not the stepping stone become a possible projectile?

Thanks for the fast reply!

bob

[Bobosan]

Sure it could but possibly the downward force of blast would keep it in place albeit probably broken into pieces. Was just a thought for covering the hole. Anything you put inside the cone to cover the hole could become a projectile.

[bob]

I shot it off a while back and have a video of it on utube now so here it is.

Details are as follows,

• 3000 grams of black powder (a slower charcoal)
• 8 liters of gasoline (In two 4 liters bags)
• 206 liters of powdered clay
• 3 3.8 cubic feet bags of compressed peat moss
• A steel cone with a 600 liter volume

The peat and clay went about 22 meters high so it was a lot bigger then my other ones.

Here are a few pictures of the cone and the stuff that was put in.

Here is the video. http://youtu.be/OmzT6AuiGz4

bob

Edited November 18, 2013 by bob

[Bobosan]

That looked great! It looked like some of the peat caught fire but I suppose it was just BP smoke. I'm surprised there wasn't a huge fireball from the peat dust but guess the particle size was large.

 

Good job. How did the cones hold up?

[psyco_1322]

That was pretty good looking, looked like something straight out of Hollywood. It doesn't look like the gas bags went though, I'd maybe try placing them directly on top of the lift charge.

[dave321]

 

Here is the video. http://youtu.be/OmzT6AuiGz4

bob

that's a great effect, reminds me of the explosion in the HURT LOCKER.

 

presume it was homemade bp, 3kg is quite a lot to use

 

have you got the cone dimensions top and bottom diameters for reference?

[bob]

Thanks for the complements guys!

 

@bobosan, some of the peat may have caught fire because when I first set it up one of the bags of gasoline got a hole and so some of the peat would have been soaked in gasoline. The cone held up well with no visible damage. In case your wondering I ended up just packing some damp clay in the bottom of the cone to plug up the hole as best I could.

 

@Psyco_1322, yes I don't think the gasoline caught either, if I do this again I'll put the gasoline directly on top like you say.

 

@dave321, yes it was home made BP, the main reason why I used so much was because I used spruce charcoal, which I found to be fairly slow; and I thought in this case as long as I don't split the cone it would be better to use too much then too little, it is a explosion simulation after all. The cone had a diameter of 150cm at the top; 100cm tall; and the bottom (it wasn't a complete cone but had the bottom cut off) had a diameter of 30cm.

 

Thanks again for the kind words.

bob

[psyco_1322]

I don't think your going to hurt that cone at all. It looks like one thick, heavy, steel plate. We shoot multibreaks from steel that's a lot thinner than your cone, with much more pressure on the metal.

[Mortartube]

Bark chippings from the garden centre add a lightweight visible debris that can look like stones when mixed with moss and peat. Much depends on the distance people are when it is set off.

[bob]

I don't think your going to hurt that cone at all. It looks like one thick, heavy, steel plate. We shoot multibreaks from steel that's a lot thinner than your cone, with much more pressure on the metal.

 

Yes I think your quite right.

Bark chippings from the garden centre add a lightweight visible debris that can look like stones when mixed with moss and peat. Much depends on the distance people are when it is set off.

I like this idea, bark chips won't have to be picked up and should be light enough to not be a hazard, assuming everybody is a safe distance from the cone.

bob

[bob]

Well spring is on its way now and I am getting excited about explosion simulations again.

 

In the first utube video yvariro posted there are several effects that I want to replicate.

 

At 25 seconds you see a man firing a presumably fake bazooka, I think it is a very cool effect and I want to be able to do it, suggestions?

 

At 1.20 you see a short and wide explosion simulation that has a lot of flame and white dust. from looking around on utube it seems that this is either a shallow steel cone, a large lifting charge (in my case I will be using

black powder), several bags of gasoline, and then it is all topped up with flour. Or it is a plastic container (perhaps one could use a twenty liter plastic pail) with a lift charge in the center, then bags of gasoline, then flour, and then the hole thing is sealed up. My main questions are if it is flour how do they keep it from lighting, and is it a steel cone or a plastic/paper container that gets blown up?

 

At 1.38 you see a very nice low to the ground fire ball, this is most defiantly a shallow steel cone with a decent lift charge and a lot of gasoline. Any guess's on how big of a cone they used, and if they just poured the gas in the cone or if put it in baggy's?

 

Another explosion simulation I want to make is one that will be using the same cone as the one I posted back in November, however I will be using compost instead of the powdered clay (too much work) and peat moss (too much money), any thoughts on how this might change the lift charge requirements? I will also be putting the black powder lift charge (some where between 2000 and 2500 grams) inside one of those protein powder containers instead of a ziplock baggy so as to gain some confinement, any thoughts on how much of a difference this will make? I will also be putting some rocket candy chunks in the lift charge to up the possibility of the gasoline lighting, and add a little bit of Hollywood, any thoughts on how effective this will be at lighting the gasoline? One of the last note worthy differences is I will be putting the gasoline in milk jugs instead of ziplock bags so as to lower the chances of a leak, any thoughts on how this will effect it? Oh yeah and I will also be putting on some bark chips into the magical mixture.

 

One more effect I am interested in is how to make a blow out window. Let me explain this blow out window thing though, it is for a scene where a man (I will be using a dummy) fires a bazooka through the window of a house, and obviously the window will have to be blown out when the projectile enters the house. My guess is that I could first cut a hole for the window (and yes this is a prop not my actual house), then take about four pieces of clear plastic and get them to cover the window hole (making sure that they will easily fall out) and then place a gas mine like the ones wily made on the inside of the window and pointing to the outside, and another mortar full of card board and flour right beside it. The below drawing should simplify this a little bite.

 

Any suggestions very much appreciated.

bob