A position sensor system, comprising: a rotary fluid effector comprising a housing having an inner surface defining a cylindrical cavity defining a central axis, and a moveable body having a first face and a second face opposite the first face and configured for reciprocal movement within the housing and configured to contact the inner surface and subdivide the cylindrical cavity to define a first fluid chamber at the first face and define a second fluid chamber at the second face, the moveable body being a piston head configured for semi-elliptical movement within the cylindrical cavity about the central axis and defining an acoustic interface (570a, 570b) in a first portion of the housing proximal an axial position of the piston head within the cylindrical cavity; an acoustic transmitter system configured to emit a first emitted acoustic waveform elliptically through a second portion of the housing about the central axis in a first direction toward the first portion, and emit a second emitted acoustic waveform elliptically through a third portion of the housing about the central axis in a second direction opposite the first direction toward the second portion; and an acoustic receiver system comprising i) a first acoustic receiver arranged proximal the acoustic transmitter system and configured to detect a first reflected acoustic waveform based on a first reflection of the first emitted acoustic waveform based on the moveable body, and ii) a second acoustic receiver arranged proximal the acoustic transmitter system and configured to detect a second reflected acoustic waveform based on a second reflection of the second emitted acoustic waveform based on the moveable body; wherein the position sensor system is configured to determine a first position of the acoustic interface based on the first reflected acoustic waveform and the second reflected acoustic waveform. a rotary fluid effector comprising a housing having an inner surface defining a cylindrical cavity defining a central axis, and a moveable body having a first face and a second face opposite the first face and configured for reciprocal movement within the housing and configured to contact the inner surface and subdivide the cylindrical cavity to define a first fluid chamber at the first face and define a second fluid chamber at the second face, the moveable body being a piston head configured for semi-elliptical movement within the cylindrical cavity about the central axis and defining an acoustic interface (570a, 570b) in a first portion of the housing proximal an axial position of the piston head within the cylindrical cavity; a housing having an inner surface defining a cylindrical cavity defining a central axis, and a moveable body having a first face and a second face opposite the first face and configured for reciprocal movement within the housing and configured to contact the inner surface and subdivide the cylindrical cavity to define a first fluid chamber at the first face and define a second fluid chamber at the second face, the moveable body being a piston head configured for semi-elliptical movement within the cylindrical cavity about the central axis and defining an acoustic interface (570a, 570b) in a first portion of the housing proximal an axial position of the piston head within the cylindrical cavity; an acoustic transmitter system configured to emit a first emitted acoustic waveform elliptically through a second portion of the housing about the central axis in a first direction toward the first portion, and emit a second emitted acoustic waveform elliptically through a third portion of the housing about the central axis in a second direction opposite the first direction toward the second portion; and an acoustic receiver system comprising i) a first acoustic receiver arranged proximal the acoustic transmitter system and configured to detect a first reflected acoustic waveform based on a first reflection of the first emitted acoustic waveform based on the moveable body, and ii) a second acoustic receiver arranged proximal the acoustic transmitter system and configured to detect a second reflected acoustic waveform based on a second reflection of the second emitted acoustic waveform based on the moveable body; wherein the position sensor system is configured to determine a first position of the acoustic interface based on the first reflected acoustic waveform and the second reflected acoustic waveform.