I had to perform some quite extensive tests to determine the effects of different variables and figure out how to optimize the spray of foam. I used the same electronic relay system I had built just months before for the pyramids of Aida to fire the cannons. Implementing that system, I was able to time a stylistic delay of a few fractions of a second between each shot so that the upstage cannons would fire just slightly before the downstage cannons, bringing a shower of foam falling from upstage to downstage.
This project turned out to be especially intense and dramatic. Due to a communications error, we didn't receive the solenoid valves used to fire the cannons until the day of the show. School was that day, too, so I had a total of about three or four usable hours until the show to get the cannons built and preform the tests I needed to do. One of the four cannons had an air leak in the tank, which I tried to mend, but it could not be saved in the time I had, so I did not bother to use it. Before the show, I pressurized the tanks and packed the barrels with foam, spraying it with Pam periodically as I packed it to lubricate the barrel, to keep the foam from sticking to itself, and to fill small air leaks between the foam. I had done all that was in my power to see that the cannons would work as I had planned, but even so, because of the unpredictable nature of some of the tests I had done and the countless variables that could have gone wrong, I had no idea if it would work or not. The tension of not knowing what would happen as we approached the moment of truth in the show was intense. It happened, and they did work. Victory.
Unfortunately, I do not have video of the event during the performance. However, I do have this test footage I took, firing the cannon at a friend.
The elephant scream heard in the video, caused by release of excess air in the tank after firing, was silenced for the show by having the valves close very quickly after opening. They were open just long enough for firing to happen, but not so long that the noise could be heard.