Interesting part about the magnetic encoder:
Mode 3.x: Brushless DC Motor Commutation Mode
In addition to the absolute encoder output over the SSI interface, this mode provides commutation signals for
brushless DC motors with either one pole pair or two pole pair rotors. The commutation signals are usually provided
by 3 discrete Hall switches, which are no longer required, as the AS5040 can fulfill two tasks in parallel: absolute
encoder + BLDC motor commutation.
If we would also use hall sensors we could eliminate the need for motor initialization, eliminating the free short move done when starting the servo.
If this sensor is precise and the motor is magnetically sealed (no large magnetic fields escape the motor when energising coils) then this could be indeed a good and cheap solution. Also seems very easy to mount and tolerances are good.
Mihai