A system includes a fixed-displacement fluid pump, a motor operatively connected to the fixed-displacement fluid pump, a sensor configured to sense a parameter related to a drive speed of the motor, and a user interface. The pump controller is configured to receive an input from the user interface of a target flow rate of the pump, determine a duty cycle for the motor based on the target flow rate, and control the motor to operate according to the duty cycle. The pump controller is further configured to receive an indication of the sensed parameter related to the drive speed of the motor, determine a measured drive speed of the motor based on the sensed parameter, and iteratively adjust the duty cycle based on a difference between the measured drive speed of the motor and an expected drive speed of the motor.