Gas or fluid driven mechanical stepper motor

A method to rotate an axis of a stepper motor in surgical instruments or chemical plants, the stepper motor including a housing, in which a cylindrical rotor fixed on a central shaft can rotate but not translate along an axial direction, characterized in that there are cylindrical translators on both sides of the rotor, where the translators are sealed fit in a cylindrical space within the housing and around the central shaft and where the translators can only translate in an axial direction, where in one axial position of a translator a set of triangular asymmetric teeth located on the translator can interact and fit into a set of triangular asymmetric teeth on the rotor, where a shape of the teeth on both sides of the rotor is symmetric and where one of the sets of teeth between one translator and the rotor and a set of teeth between the other translator and the rotor are tangentially shifted over a length equal to half a width of a tooth and where the translators can be moved by a pressure difference between the part of the cylindrical space between the housing and a translator and the part of the cylindrical space between the translator and the rotor, comprising:

• alternately applying a high pressure gas to the space between the housing and the back surface of one of the translators and a low pressure gas to the space between the housing and the back surface of the other translator, while keeping the space between the translators and the rotor permanently at an intermediate pressure.