A coreless electromagnetic machine comprising: a dual rotor adapted to rotate about an axis, the dual rotor including inner and outer rotor segments , wherein the outer rotor segment is spaced radially outward from and axially aligned to the inner rotor segment , and the inner and outer rotor segments radially define an annular chamber ; and a stator disposed at least in-part in the annular chamber , the stator comprising a support structure , and a plurality of bobbins detachably fitted to the support structure, and a plurality of electric coils with each one wound about a respective bobbin of the plurality of bobbins and each including an inner winding layer wound about and spaced from a centerline that generally intersects the axis, wherein the outer rotor segment and the stator radially define an annular outer gap as part of the annular chamber , and the inner rotor segment and the stator radially define an annular inner gap as part of the annular chamber , and characterised in that each bobbin defines first openings for the flow of cooling air radially between the annular inner and outer gaps ; wherein the inner rotor segment and the outer rotor segment each include a respective plurality of second openings , the first and second openings being suitable for the radially outward flow of cooling air , and wherein the second openings of the inner rotor segment and the outer rotor segment are at the same axial positions as the first openings of the bobbins , wherein at least four of the second openings of the inner rotor segment correspond to the at least four second openings of the outer rotor segment in their axial and circumferential positions, and wherein exactly two axial positions are provided for the first and second openings . a dual rotor adapted to rotate about an axis, the dual rotor including inner and outer rotor segments , wherein the outer rotor segment is spaced radially outward from and axially aligned to the inner rotor segment , and the inner and outer rotor segments radially define an annular chamber ; and a stator disposed at least in-part in the annular chamber , the stator comprising a support structure , and a plurality of bobbins detachably fitted to the support structure, and a plurality of electric coils with each one wound about a respective bobbin of the plurality of bobbins and each including an inner winding layer wound about and spaced from a centerline that generally intersects the axis, wherein the outer rotor segment and the stator radially define an annular outer gap as part of the annular chamber , and the inner rotor segment and the stator radially define an annular inner gap as part of the annular chamber , and characterised in that each bobbin defines first openings for the flow of cooling air radially between the annular inner and outer gaps ; wherein the inner rotor segment and the outer rotor segment each include a respective plurality of second openings , the first and second openings being suitable for the radially outward flow of cooling air , and wherein the second openings of the inner rotor segment and the outer rotor segment are at the same axial positions as the first openings of the bobbins , wherein at least four of the second openings of the inner rotor segment correspond to the at least four second openings of the outer rotor segment in their axial and circumferential positions, and wherein exactly two axial positions are provided for the first and second openings . <EOS>