drazh
Either one gets this very simple technique from the start ("by accident") or one is forced to think about the mechanics/ get a lesson or two from people who understand the mechanics and who can help with metaphors and precise exercises to solve your problem for your case (hand size and its general level of development, for example, may also be a factor for picking this or that approach).
In terms of body control, it's a combination of:
1) perfect rotational freedom, which will most likely have to be trained to achieve it;
2) activity of the fingertips/pads (and their reaction to the mechanical workings of the key), which certainly has to be trained, felt, experienced, thought through.
As soon as you understand the simple mechanics, concentrate on the point of sound, not on jamming into the keybed. Listen for the sound result and use your energy to get what you want with intention: pre-listening, expecting each and every tone you want and correcting its quality accordingly. The faster you go, the more economic your movements will have to be, but nature tends to take care of that rather well.
Patience is also a factor. You cannot force this. I would say that if you want really quality execution of such a tremolo and not some random shaking to and fro, then there is certainly a correlation with how well you do usual, simple trills with all finger combinations. Expecting much more than that tempo within a certain time limit is simply not realistic.
Find a teacher!