Hoverboard + encoder for self-balancing robot?

I would like to “sensorize” two hoverboard motor wheels with CUI AMT102-V encoder.
But, since the hoverboard BLDC don’t have an output shaft, I don’t really know how to attach the sensor…
Should I use a pulley with a timing belt between the wheel and the encoder?
Or should I use gear?
Or something else ^^?

Thanks in advance!

You could drill and tap the rotor endcap (should be removable) with a bolt circle to accommodate your encoder wheel, or 3D print an encoder wheel with IR beam sensor on a custom bracket. You may also be able to print a part that uses the existing bolts on the hub motor, and use longer m4 screws to hold the endplate on.

can draw a quick sketch about your idea ?

I believe most hooverboard motors have a Hall effect encoder built in. It’s the thinner 5 wires. The one I tested provided 90 pulses per revolution which should be enough for your application