An apparatus for use in a magnetic resonance (MR) system, which generates an external MR magnetic field, is provided. A rotor comprises a rotor shaft with an axis along a length of the rotor shaft and a plurality of coils on the rotor shaft. A housing supports and surrounds the rotor, where a part of the housing surrounds sides of the rotor and where the part of the housing surrounding sides of the rotor is magnet free. A mount allows for the mounting of the housing to the MR system in a location where the MR system provides a magnetic field, wherein a component of the MR magnetic field that is perpendicular to the axis of the rotor shaft is at least 100 Gauss. An active timer applies a voltage to the plurality of coils with alternating polarity. Contacts provide an electrical connection between the active timer and the plurality of coils.