Difficulty with Taps / Trills / Rolled R
For whatever reason, I have trouble rolling my r after the letter t or d. Grito, grande, and guarda come out fine but trimestre leaves me sounding like a drunk toddler. At best, I get an overly long roll rather than the tap I think I'm supposed to be doing. Any advice?
Before starting, I recommend you try to do a continous R, such as this woman does in this vídeo: https://www.youtube.com/watch?v=gAla47geXFA
This is a legitimate Portuguese R. (Single R between vowels and in combination with consonants in "tr, dr, gr, etc.")
Well, you probably have already realized that the "T", the "R" and the "D" all use the "tip of the tongue" against the front part of the top of your mouth.
(Did you know we call it "céu da boca"? Mouth's sky)
But if you look closer, you will see that "t" and "d" will, if not, almost touch the teeth, while "r" will be kept a little farther from the teeth.
"T" and "D" use the tip of the tongue in a very protuberant part of the roof.
"R" uses also the tip of the tongue, but it will vibrate just a little behind that very protuberant part of the roof. A little more far away from the teeth.
- So, a little less tip of the tongue, and a little less tip of the roof.
Explode x Sustain
Now "R" is very very special compared to "T" and "D".
"T" and "D" are a "single explosion". (They are actually the exact same, but "D" gets voice before exploding). No one could ever do a long T or a long D. They're airtight.
But "R", you can sustain an "R" as much as your breath can last.
Knowing this, you can start thinking about the transition in "TR" and "DR". It passes from the very tip of the tongue to what is immediately behind it. From an explosion to an indefinitely sustainable vibration.
That's why I say: learn to sustain you "R" indefinitely. Only then you're actually saying an "R", and only then you will know what differs "R" from "T" and "D".