Csdrhrt

I'm trying to pass a melody from my head to the sheet and it consists of 29 eighth-note-triplets but I can't figure out how to break them into measures.

If I start with 4/4, I can fit 2 measures of 12 triplets each and ill have 5 leftover, but I can't find a time signature for these leftovers.

First thing to do is to listen very carefully, and establish wher in the bar any of the main notes come - the emphasised ones that in a standard 4/4 bar would arrive on beats 1 and 3, and then work out what happens on beats 2 and 4. That will give a fair idea of placement of some of the notes.

29 seems odd (it usually is) so is there a possibility that the 30th note is at the end of a bar, rather than being the 1st note in a new bar?

I think the first thing you should ask yourself is whether notating this rhythm as eighth-note triplets is actually necessary. Could this just as easily be done with two measures of 12/8 followed by a (only slightly unusual) 5/8 measure? Only if there’s another instrument playing straight eighth notes, or something else about the context that makes eighth-note triplets vastly more natural would I even consider notating this idea as triplets. Seriously consider it, because the full solution is extremely unusual, and most musicians won’t even recognize it.

Here it is: if you really need for these notes to be triplets the whole way instead of (the identical sounding) eighths of compound time, then you could notate this idea as two measures of 4/4 followed by a measure of 5/12. Such time signatures are often called “irrational” time signatures, although that’s a terrible name. Just as one fourth of a whole note is a quarter note—hence 4 in the signature—and one eighth of a whole note is an eight note—hence 8 in the signature—an eighth-note triplet is one twelfth of a whole note. These time signatures are deeply unfamiliar to most people, and many performers take offense at them. Be warned.

I agree with @Tim that figuring out where the emphasis falls is definitely key. The other key question is what is supposed to come after those 29 notes — maybe there is a plausible remainder of the 3rd measure. Or maybe the first 5 triplets were an anacrusis to the first measure?

The kind of music I can think of where 29 triplets could constitute a complete section of a song would be Eastern European or Middle Eastern folk dances, where people settle for odd meters as a rough approximation of the true underlying pulse.

So if you are e.g. an Armenian Jazz composer, feel free to write a measure in 29/12th time. If you see yourself in more of a traditional Western European tradition, odds are that your melody in reality has a more conventional rhythmic arrangement, and just just have not quite found the right groove for it yet.

I don't know if that can help:

30 notes, here, in this Nocturne op. 15 n°2 by Chopin