How do you get a rainstick to go more than 20 seconds at a 45 degree angle using rice and lentils and some navy beans for a science project?

I'd try a bunch of interior baffles part way across the opening, so the beans couldn't simply fall to the other end. Then you'd have to experiment- Should they be flat or curved? Should they be arranged so they are in a spiral and each baffle dumps onto the next in turn.Or should they be randomly placed? How large should the openings to the next layer be? Sounds like an interesting project!