A downhole oscillation tool for a drill string, the downhole oscillation tool comprising: a pulse motor including: a rotor having at least two helical lobes along a length of the rotor; and a stator surrounding a stator bore, the stator having at least three helical lobes along a length of the stator, wherein the rotor is located in the stator bore and configured to nutate within the stator; and a pulse valve assembly located downstream from the pulse motor, the pulse valve assembly including: a first valve plate configured to nutate with the rotor, the first valve plate including a plurality of first ports (134, 136); and a second valve plate (138; 148) located downstream from the first valve plate, the second valve plate including a plurality of second ports (140, 142), wherein the second valve plate is fixedly coupled to the stator and abuts the first valve plate to form a sliding seal, characterised in that: the plurality of first ports (134, 136) includes at least one first radially outer axial port defined in the first valve plate and at least one first radially inner axial port defined in the first valve plate; the plurality of second ports (140, 142) includes at least one second radially outer axial port defined in the second valve plate and a plurality of second radially inner axial ports defined in the second valve plate; each of the first and second valves plates (132, 138) has a central axis, each of the first and second axial ports (134, 136, 140, 142) has a central axis, each of the radially outer axial ports (134, 140) has a central axis that is radially farther from the central axis of the respective valve plate (132, 138) than the central axis of each of the radially inner axial ports (136, 142) of the same valve plate; and in that at least one of the first ports (134, 136) is in fluid communication with at least one of the second ports (140, 142) through all positions of nutation of the first valve plate relative to the second valve plate. a pulse motor including: a rotor having at least two helical lobes along a length of the rotor; and a stator surrounding a stator bore, the stator having at least three helical lobes along a length of the stator, wherein the rotor is located in the stator bore and configured to nutate within the stator; and a rotor having at least two helical lobes along a length of the rotor; and a stator surrounding a stator bore, the stator having at least three helical lobes along a length of the stator, wherein the rotor is located in the stator bore and configured to nutate within the stator; and a pulse valve assembly located downstream from the pulse motor, the pulse valve assembly including: a first valve plate configured to nutate with the rotor, the first valve plate including a plurality of first ports (134, 136); and a second valve plate (138; 148) located downstream from the first valve plate, the second valve plate including a plurality of second ports (140, 142), wherein the second valve plate is fixedly coupled to the stator and abuts the first valve plate to form a sliding seal, a first valve plate configured to nutate with the rotor, the first valve plate including a plurality of first ports (134, 136); and a second valve plate (138; 148) located downstream from the first valve plate, the second valve plate including a plurality of second ports (140, 142), wherein the second valve plate is fixedly coupled to the stator and abuts the first valve plate to form a sliding seal, characterised in that: the plurality of first ports (134, 136) includes at least one first radially outer axial port defined in the first valve plate and at least one first radially inner axial port defined in the first valve plate; the plurality of second ports (140, 142) includes at least one second radially outer axial port defined in the second valve plate and a plurality of second radially inner axial ports defined in the second valve plate; each of the first and second valves plates (132, 138) has a central axis, each of the first and second axial ports (134, 136, 140, 142) has a central axis, each of the radially outer axial ports (134, 140) has a central axis that is radially farther from the central axis of the respective valve plate (132, 138) than the central axis of each of the radially inner axial ports (136, 142) of the same valve plate; and in that at least one of the first ports (134, 136) is in fluid communication with at least one of the second ports (140, 142) through all positions of nutation of the first valve plate relative to the second valve plate. the plurality of first ports (134, 136) includes at least one first radially outer axial port defined in the first valve plate and at least one first radially inner axial port defined in the first valve plate; the plurality of second ports (140, 142) includes at least one second radially outer axial port defined in the second valve plate and a plurality of second radially inner axial ports defined in the second valve plate; each of the first and second valves plates (132, 138) has a central axis, each of the first and second axial ports (134, 136, 140, 142) has a central axis, each of the radially outer axial ports (134, 140) has a central axis that is radially farther from the central axis of the respective valve plate (132, 138) than the central axis of each of the radially inner axial ports (136, 142) of the same valve plate; and in that at least one of the first ports (134, 136) is in fluid communication with at least one of the second ports (140, 142) through all positions of nutation of the first valve plate relative to the second valve plate.