Virgil Donati does a circular roundhouse movement when he get up to speed on his single strokes. He admits it is something that just happens and is neither advantageous or detrimental. Just a physical quirk he has acquired.
Play Judas Priest "Rapid Fire" with your left foot a few times. It should develop a lot of feel in your left ankle and teach it to move like your right.My left leg is horrid at this technique. I still end up using more of my leg instead of the ankle.
It's the ankle technique where your heel is "floating" or just simply a small bit above the footboard. It's essential for the swivel technique, which is what I want to learn but still need work on my left.Not sure what you mean by "floating double bass"
are you referring to heel up playing?
there are tempo shifts where it goes from leg, to leg and ankle, to full ankle.
the best thing to suggest is to use a metronome and increase it and play to it.. it takes a long time to get good at this.. if your pushing to far to fast your ankle will start to swivel to get the hits.
That being said the swivel technique is a way that some drumers will get good at and be able to play very fast using it.
are you doing 16th notes?
how long have you been working at double bass?