A brushless starter-generator assembly, comprising: a stator assembly comprising a stator stack, a magnetic sleeve located around an outer circumference of the stator stack, and a non-magnetic separator located between the stator stack and the magnetic sleeve; a rotor including a magnetic hub and rotor poles and disposed at least partially within the stator assembly, the rotor being configured to rotate about an axis; and a field coil surrounding a portion of the stator assembly and located radially outward from the rotor with respect to the axis, the field coil including first and second field coils (32a, 32b), each disposed around a point on the axis and within an axial width of the stator stack in a direction of the axis, the first and second field coils (32a, 32b) being formed in respective first and second grooves in the stator stack, the first and second grooves being located at respective opposing axial ends of the stator stack, wherein the field coils (32a, 32b) are: located directly radially outwardly from the rotor poles; spaced apart from each other in the direction of the axis; and adjacent to ends of the non-magnetic separator in a longitudinal direction, wherein an outer circumference of the field coils (32a, 32b) contacts an inner circumference of the non-magnetic separator; and wherein the magnetic hub has a magnetic permeability that decreases based on a strengthening of a magnetic field generated by the field coil. a stator assembly comprising a stator stack, a magnetic sleeve located around an outer circumference of the stator stack, and a non-magnetic separator located between the stator stack and the magnetic sleeve; a rotor including a magnetic hub and rotor poles and disposed at least partially within the stator assembly, the rotor being configured to rotate about an axis; and a field coil surrounding a portion of the stator assembly and located radially outward from the rotor with respect to the axis, the field coil including first and second field coils (32a, 32b), each disposed around a point on the axis and within an axial width of the stator stack in a direction of the axis, the first and second field coils (32a, 32b) being formed in respective first and second grooves in the stator stack, the first and second grooves being located at respective opposing axial ends of the stator stack, wherein the field coils (32a, 32b) are: located directly radially outwardly from the rotor poles; spaced apart from each other in the direction of the axis; and adjacent to ends of the non-magnetic separator in a longitudinal direction, wherein an outer circumference of the field coils (32a, 32b) contacts an inner circumference of the non-magnetic separator; and wherein the magnetic hub has a magnetic permeability that decreases based on a strengthening of a magnetic field generated by the field coil. located directly radially outwardly from the rotor poles; spaced apart from each other in the direction of the axis; and adjacent to ends of the non-magnetic separator in a longitudinal direction, wherein an outer circumference of the field coils (32a, 32b) contacts an inner circumference of the non-magnetic separator; and wherein the magnetic hub has a magnetic permeability that decreases based on a strengthening of a magnetic field generated by the field coil.