I loved reading these tips! I too want to have smooth bow direction changes. I’m a beginner so I have a lot of work to do still to achieve this but I really like this exercise I saw in a video a couple of weeks ago. I’ll try to describe it.
1. Start at the frog
2. At 1/4 of the bow lift the pinky finger
3. At 2/4 lift the third finger
4. At 3/4 lift the middle finger
5. At the top put down the middle finger
6. At 3/4 put down the third finger
7. At 2/4 put down the pinky finger
8. At 1/4 lift the index finger
9. At the frog put down the index finger
10. Repeat the entire process
While doing this you should make the lifting and putting fingers as inaudible as possible. It’s a great exercise to feel how each finger participates in the bowing process. Sometimes when I do this exercise I almost can’t hear the bow change at the frog so I think this is really a great exercise to learn and feel how to smoothly change bow directions. Hope it’s helpful.