Balanced and unbalanced load detection

A motor controller for a rotary machine comprising a drum for containing a plurality of load portions driven for rotation about a rotation axis by a motor, the motor controller being configured to estimate an unbalanced load on the drum by:

• i) measuring a rotational speed of the drum during a first time period over a first complete rotation of the drum while the motor is driven under constant torque control;
• ii) determining a maximum speed angle during the first time period as a rotational angle of the drum over the first time period at which the rotational speed of the drum is a maximum;
• iii) measuring torque and rotational speed during a second time period over a second complete rotation of the drum starting at the maximum speed angle offset by a predetermined advance angle while the motor is driven under constant torque control;
• and
• iv) calculating an estimated unbalanced load of the drum from measurements of torque and rotational speed over the second time period and a difference in rotational speed over first and second halves of the second time period.