I was going to suggest syncing red and yellow lights with the fog machine firing a short burst just before the lights and air cannon are triggered as well. As impressive as the video is, most of us can't quite swing the $200 valves to suck the fog in and mix it with the fog. The cheapest way I've seen was down in Mexico on a pirate cruise where they just dropped a firecracker down the muzzle of their metal barreled cannons. I certainly don't suggest doing that with anything made of PVC or paper though! Or were you were looking for a simulation of the explosion where the 'cannonball' landed? If yo udon't want to reload the flour for each shot of the air canon (I'm not sure if there's a non Rube Goldberg way to sprinkle the flour so a water spitter might be your best bet, especially if you're going for a naval battle type scene. Some of the bigger spitters really pump out a serious amount of water too! If it's land based, you could have things lean away from the 'explosion', stop, and then reset for the next sequence. Think of a large rocker setup but stopping at 180 degree rotations. You may need an eccentric cam and two micro switches to set the open/closed positions for the wiper motor to start and stop on.
