PeterH:
The basic approach might work, but I suggest if you're trying to make the can fall over then 'really fast' is not a good way to do it. You want as much weight as you can get, as high up and as far away from the central axis of the can as possible, and then spin it around that axis at about the same frequency that the can will naturally wobble if you put it on end and then spin it so the base rolls around in a small circle. That way your weight will drive the natural resonant frequency of the motion and tend to amplify it. If you try to drive it much faster, it's likely to just sit there rattling. Once you have the hardware in place you'll be able to experiment and see what speed works best. I would have thought that a rigid rotor would work a lot better than a weight on a string.
hmmm, this is very insightful. I don't have a great understanding of physics (currently in Physics 1), but I can see what you are saying. A rigid rotor might actually work better. I really don't know. We'll probably go with whichever way is easier/cheaper for us to put together.