A machine includes a rotor supported to rotate about a rotational axis and an actuator arranged to act on the rotor and control a position of the rotor about the rotational axis. A bladed turbomachine wheel is coupled to the rotor and has blade tips that pass closely to an adjacent, non-rotating surface. A sensor is adjacent to the turbomachine wheel and arranged to sense the blade tips and output a position signal representative of the position of blade tips relative to the sensor. A controller is coupled to the sensor and the actuator and is adapted to receive the position signal from the sensor and generate and send a control signal to the actuator to control the position of the rotor based on the position signal from the sensor.