Here's the tube with a mute (a 2 liter bottom) and some mouth pieces we tried. The small section of larger vinyl tubing as a mouthpiece is playable, but a small section of pvc worked better, but not great. Given the success the pvc we tried boring out the inside of a identical pvc pipe to make the opening bigger, this resulted in an even more playable mouthpiece. I noticed that you could get higher notes more easily with this mouth piece. Hoping this trent of wider and stiffer would be better we tried gluing the very top section of a 2 liter to a pvc pipe to make a super wide mouth piece, this was did not work as planed. The horn was very easy to sound, but getting high notes was nearly impossible, as you couldn't close your lips tight enough with the wide opening .
Given the surprising variety of results planning an activity based on making a curtain timbre (character of sound) with a tube trumpet or similar instrument might be possible in the future.
Sound Automata: Drum Machine
Here's the automata in action playing on a tea tin (sorry for the uninspired rhythm).
We plan to develop a few standard models of this and post them in the future, stay tuned.