For Twelfth Night, the director wanted a funerary urn trick. When the actor knocks it over, he wanted the lid to fall off and a puff of ashes to fly out. I decided on a pneumatic solution.
Early on, we decided the urn should be on a base which was hinged to the floor, which would keep the urn from rolling down the hill into the audience, and also have it fall in a consistent manner during every show.
This trick is actually extremely simple in concept, and pulling it off only requires a minimum amount of research to find the right parts.
The idea behind it is the same as filling a straw with corn starch and blowing it out. Instead of a person blowing it out, I have a tank of air which is filled before hand. And instead of a person deciding when to blow, I have an electric valve which is triggered when the urn hits the ground.
The tank of air is just a soda bottle. I fitted a tire valve onto the cap; I got it from an old tire, though you can buy them new if you wanted. A hose runs out the back of the bottle into the valve, which then runs to a hole in the stage which holds the corn starch. The valve runs off of eight AA batteries, though it can be changed to be plugged into the wall. Finally, I wired in a button between the valve and the batteries, which is on the stage floor where it can be pressed by the urn when it hits the ground.
Here is a video of it in action: