If nothing in my last post made any sense, this is what I was trying to say:
I used my good camera w/ directional microphone, and set up the scooter frame so that it would resonate. The difference is pretty clear here. Everything you hear translates to what you would feel while riding it, so the ride will be much smoother as well.
I finally worked out all the sign (+/-) kinks. The remaining task is to make it fault-tolerant and load test. The Hall effect sensors are not perfect, and they can occasionally throw in a false signal or miss a real signal. This becomes even more important when they are being relied upon for a speed estimate that drives the sine waves. The motor and MOSFETs should be able to tolerate a glitch like this, but at high speeds it can cause a draw-down on the main capacitor, which can sometimes cause the microcontroller to spontaneously jump out of the program loop. So it would be better if this didn't happen...
More to come.