How did you learn to do trills? Did you practiced, or just slowly got it through pieces? Any recommendations?

I've been trying to do it for my piece for a few months now, but its still a complete disaster and im starting to feel VERY frustrated.

I can do anything else in the piece just fine, and i can do a slow baby prototype of a trill on time, but as soon as i try to put some freedom into it, i either feel my fingers stiff and my tendons hurt, or i mess up all the tempo.

I even tried watching some youtube "trill tutorial" videos but i can't reproduce what they show without feeling im forcing my hands, so i guess im doing something wrong.

I asked my teacher for help, but he would just insist to keep that trill wanabe im doing right now and don't think too much about it. But i just can't do it, so i would like to know how did you learnt to do trills.

I don't remember ever finding it difficult to play a trill in general (or having to practice trills), but in a particular musical context it may be difficult to get to a position in which trilling is comfortable. I tell my students to imagine themselves spinning a top. The idea is that the brain gives the fingers only one command ("trill"), rather than a separate command for each note in the trill. Think of the trill as a single event or musical gesture, not as a series of events or musical gestures. Try to be natural, relaxed, and not self-conscious. In a particular musical context, try to use the stronger, lower fingers, if at all possible.