Recently I have bought some vibration motors to make a Braille display. But when I attach them to my hands, I can't tell which motors are vibrating so many times. So I am a little confused now: Can vibration motors be used for it, to be used as Braille dots?
It would be very hard to do so unless you had very precise motors whose vibrations only go through a short distance on a soft surface.
To get a "visual" why, place one of your hands on a table then with the other hand, lightly hit the table. With a good, stable table, you should feel a slight vibration. This is because of one, a table is very rigid and quite dense (may vary) and thus are able to conduct vibrations very well. Also the more force you use, the stronger the oscillations (and thus the stronger the vibrations).
It would be most helpful to have rather weak motors that vibrates only a rigid surface (maybe circular) right above it for instance. The rest of the mat or whatever is used to vibrate is instead made of something that does not vibrate easily. With the bad example below, the red circles indicate the surface where the vibrator will vibrate and the white will represent the surface that should not vibrate at much: