The 470ohm resistor and 9v battery combo = 5v was used because it limits the current some what and safer than using 4 AA batteries which would give 6v or 3 AA batteries at 4.5v and capable of to much current
Another type of Hub Motor see pic
BOTTOM pic of faulty Hall sensor C was rubbing against magnets making the wheel feel bumpy as I turned it over when I first got it , Hall sensor A had bad solder joints , Hall sensor B was the only one working properly