A magnetic/encoder assembly has a compact design and combines the features of motor, encoder and chuck locating feature within a single motor housing. The motor/encoder includes a DC brushless motor with an inner magnetic rotor. The motor windings and the commutation electronics are mounted towards the bottom side of a printed circuit board. The rotor of the motor is extended above the surface of the printed circuit board. The extended rotor provides a precision seat for the magnetic wheel with multiple poles. The top surface of the printed circuit board mounts the sensor for the encoder. The extension of the rotor provides the precision mounting surface of the cartridge driving chuck.