New here.I am a keyboard player (wanted to be a pianist but couldn't afford it). I use yamaha PSR-E403, which has non-weighted keys.Suppose, I am improvising over F# Major pentatonic scale, which has all black notes.My fingers slip if I try to go to tempo like 80BPM with 4 notes in each beat.Also, thumb on the black keys is nightmare for me and it becomes a major problem when I have to tuck it under from my 3rd finger. Same problem occurs if i am arpeggiating over F# major chord on 2-3 octaves. I do great with chords like D,E, basically, when my thumb on the white keys but whole hand on black keys feels unnatural to me. How to improve contact and controls on the black keys ? I don't have any teacher to guide me on this so, any suggestions will be appreciated.
I am not sure though but it can also be a problem of my instrument, I have seen pianos with flat shaped black keys from the top but in my instrument black keys are slight curved from the top.
P.S. I have spent quite a lot of time practicing slow.