In high school, I once tried to build a smoke-ring-generating vortex cannon out of a five-gallon paint bucket, a t-shirt, and some dry ice. My contraption was a letdown. It produced weak, wispy rings, and did so inconsistently. This video shows how to build a DIY vortex cannon that actually works.
All you need is a water bottle, a balloon, and a stick of lit incense. YouTuber Dave Hax demonstrates:
Wanna make a bigger cannon? Visit The Kid Should See This for more a more challenging instructional.