Connecting an encoder to the gearbox instead of the motor shaft is only possible in the following situations:

• A stepper motor is controlled in open loop
• A brushed (DC) motor is used
• A brushless motor equipped with digital hall sensors is used (trapezoidal commutation of the motor)

Here are the configurations that need the encoder to be present on the motor, as the device providing the commutation information does not allow the encoder to be placed on the gearbox:

• When a stepper motor is controlled in closed loop
• When a brushless motor is used, without digital hall sensors (sinusoidal commutation of the motor)

Another thing to consider is that most gearboxes have a certain backlash, so even for the situations where the encoder can be mounted on the gearbox, we advise that the encoder be connected on the motor shaft  (if possible), in order to obtain a good motor control.