By a marimba, do you mean that you will include pipes as specialized resonators? If so, it may be difficult to set up such an instrument, because the range of pitches in the rules this season is very wide, meaning you'll need many pipes, and they'll probably have to be very long to reach F3. (All instruments must fit in a 100 cm by 60 cm by 60 cm box when you arrive to the event, but they can be bigger when set up.) If you make a xylophone or glockenspiel (i.e. no pipes), that could produce nice pitches that are stable over time while also consuming less time than a marimba.What about a marimba? We did a marimba last year but we used oak since it was cheap. We are thinking of doing a maple marimba this year for better resonance. We did have some trouble with registering pitches, so a percussion based instrument may not be a great move, but it is relatively easy to build and tune. I have 3 other build events and a couple test events to work on this year, so I don't want to spend a ridiculous amount of time building and tuning an instrument while I need to work on other events. Anyone else thinking about a marimba or have ideas for fixing problems with pitches getting registered?
To be honest, I don't really know why some tuners can't pick up some instruments even when they play loudly enough. It may be due to overtones of the instrument interfering with the tuner's measurement of the fundamental. Resonator pipes, as in a marimba, might reduce interference. You could also carve off the bottom of the bars so they are shaped like arches instead of boxes to get nice integer-multiple harmonics, but this may not be best for you in terms of time since you said you want plenty of time for you other events. And of course, since I don't know why tuners fail for some instruments, this paragraph could be completely wrong.