When I am designing a complicated model, I break the major components down to much simpler ones such that I am able to print and test them individually (I like Autodesk Fusion 360 because it supports a design methodology such as this). Four Whistles is one example of such a process, and includes four types of whistles that will eventually become part of a more complicated model. I've never designed whistles before, and after searching the web for "how to design a whistle", these are what I came up with that would work in my more complicated model. And the grandkids liked them so much (the parents, well, not so much) that all I was left with was the prototypes, all printed in "draft mode", that appear in the photographs! Grandson test: https://www.youtube.com/watch?v=LfYAsUkg4v8 Whistle test: https://www.youtube.com/watch?v=ySGm7mjA2rw Even though these are fairly simple prints, I probably forgot a file or two or something, so if you have any questions, please feel free to ask. Designed using Autodesk Fusion 360, sliced using Cura 2.3.1, and printed in PLA on an Ultimaker 2+ Extended and an Ultimaker 3 Extended.