Explosions from trash cans...

[seanmcleod]

Hey guys, so I'm putting together a music video and at the climatic ending of it I need to have a build up of explosions of dirt, dust, and debris. At first a few trash cans will erupt, then a dumpster, and finally just chaos. I'm hoping to use a combination of live effects that I sweeten in post with CGI.

Anyone have any recommendations or experience with this sort of thing? I take it I will probably have to get some sort of pressurized air cannon that I pack with styrofoam debris and dust, while pumping in smoke for effect as well. Any other solutions you have used or can think of?

Also I'm going to post this in the appropriate forum but I am looking for a CGI artist to collaborate with this on for pay... so if you think it's in your wheel house let me know.

 

[clang]

Air cannons would seem a sensible option. Remember not to use real trash can lids - they'll look great, but will cause very genuine damage as they unpredictably frisbee back to the ground The dumpster lid could be equally hazardous - possibly shoot that with the lid already open, or with a hidden safety rope so it can't take flight. Yes, CGI is often a good idea to sweeten practical explosions - CGI can relatively easily add big debris (such as lids) controllably and of course safely.

Keep eye health and safety in mind too - ignoring actual injuries, no one wants a eyeful of grit and dust. The obvious issue to think about is just how close will anyone (performers or crew) be to all these practical explosions - the further the better.

I strongly recommend getting an experienced FX technician in - in fact i'd hope no reputable equipment supplier would otherwise rent you an air cannon. You and the technician can then plan some sensible, safe but cool-looking shots.

Have a look at http://www.detonationfilms.com/Stock_Directory.html - you might get lucky and find some stock explosions you can use for a couple of shots, or to sweeten the chaos at the end.

 

[seanmcleod]

Thanks clang... I'll have to check into air canons, do you think I could rent a air compressor with enough power from a Home Depot type place and make a sort of "canon" mount for it to attach to the bottom of... I'm thinking maybe the nozzle leads the the base of a funnel which opens up to a cardboard cylinder... then maybe a disc the same size as the opening is put in place at the bottom of the cylinder and dust and styrofoam debris is loaded into, then released and... bam?

 

[clang]

Home made air cannons? Sounds hard (and dangerous). The main difficulty isn't the air compression - as you say, any compressor can do that, at least at low pressure - the difficulty is controllably, safely and reliably releasing that air very suddenly to create the 'explosion'. I doubt the hardware store is going to have the appropriate bits.

Again, I strongly recommend getting an experienced FX technician - anything involving explosions is not for amateurs. Even something apparently harmless as compressed air can potentially 'shoot' debris with surprising force.

if you don't know anyone suitable or can't afford them, then maybe you should look at redesigning your shots to explode stuff in post-production - programs like Particle Illusion (which I use) and After Effects are pretty good at explosions. But in that case you need to talk in advance to your digital effects technician - there are then a whole bunch of new issues re camera movement, greenscreen, etc etc.

 

[yycadm]

I've done a little work with air cannons, and although it isn't difficult to fabricate the components, and a relatively small compressor will provide you with lots of air, the danger is controllabilitiy.
First time users frequently expect that they're going to need high pressures to make things happen, and wind up the pressure too high, creating very dangerous condittions. You can bounce a refrigerator off the ground with 15 psi, properly delivered....100 psi and the same delivery system will send that same refrigerator 30 feet in the air.
a qualified tech and a properly set up air cannon plus CGI make a lot of sense