A compound harmonic gearbox comprising: a first ground gear and a second ground gear being interconnected about a stationary shaft to form a housing, wherein only the first ground gear includes gearbox mounting features; an output flange partially encased within the housing; a flex spline within the housing that drives the output flange; a wave generator within the housing that drives the flex spline; an input shaft with an input gear that drives the wave generator, the input shaft extending through the first ground gear, wherein the output flange rotates completely around the stationary shaft by rotating the input shaft; and characterized in that: the input shaft extends through an input-shaft channel in a first radial outer shell of the first ground gear; one or more input-shaft bearings are disposed in the input-shaft channel for rotational positioning of the input shaft; and the input shaft extends radially through the first radial outer shell; and the input gear defines a first bevel gear and an axial end of the wave generator defines a second bevel gear that meshes with the input gear; the input shaft extends axially through a first axial end wall and is radially offset from an axial center of the stationary shaft; and the input gear defines a first spur gear, and an axial end of the wave generator defines a second spur gear that meshes with the first spur gear, and wherein the input shaft extends radially through the first radial outer shell of the first ground gear; and the gearbox further comprising: a stationary-shaft bearing, wherein: a portion of the stationary shaft defines a stationary-shaft bearing inner race; a stationary-shaft bearing outer race is connected to the wave generator; and a stationary-shaft bearing rolling element is disposed therebetween. a first ground gear and a second ground gear being interconnected about a stationary shaft to form a housing, wherein only the first ground gear includes gearbox mounting features; an output flange partially encased within the housing; a flex spline within the housing that drives the output flange; a wave generator within the housing that drives the flex spline; an input shaft with an input gear that drives the wave generator, the input shaft extending through the first ground gear, wherein the output flange rotates completely around the stationary shaft by rotating the input shaft; and characterized in that: the input shaft extends through an input-shaft channel in a first radial outer shell of the first ground gear; one or more input-shaft bearings are disposed in the input-shaft channel for rotational positioning of the input shaft; and the input shaft extends radially through the first radial outer shell; and the input gear defines a first bevel gear and an axial end of the wave generator defines a second bevel gear that meshes with the input gear; the input shaft extends axially through a first axial end wall and is radially offset from an axial center of the stationary shaft; and the input gear defines a first spur gear, and an axial end of the wave generator defines a second spur gear that meshes with the first spur gear, and wherein the input shaft extends radially through the first radial outer shell of the first ground gear; and the gearbox further comprising: a stationary-shaft bearing, wherein: a portion of the stationary shaft defines a stationary-shaft bearing inner race; a stationary-shaft bearing outer race is connected to the wave generator; and a stationary-shaft bearing rolling element is disposed therebetween. the input shaft extends through an input-shaft channel in a first radial outer shell of the first ground gear; one or more input-shaft bearings are disposed in the input-shaft channel for rotational positioning of the input shaft; and the input shaft extends radially through the first radial outer shell; and the input gear defines a first bevel gear and an axial end of the wave generator defines a second bevel gear that meshes with the input gear; the input shaft extends axially through a first axial end wall and is radially offset from an axial center of the stationary shaft; and the input gear defines a first spur gear, and an axial end of the wave generator defines a second spur gear that meshes with the first spur gear, and wherein the input shaft extends radially through the first radial outer shell of the first ground gear; and the gearbox further comprising: a stationary-shaft bearing, wherein: a portion of the stationary shaft defines a stationary-shaft bearing inner race; a stationary-shaft bearing outer race is connected to the wave generator; and a stationary-shaft bearing rolling element is disposed therebetween. a stationary-shaft bearing, wherein: a portion of the stationary shaft defines a stationary-shaft bearing inner race; a stationary-shaft bearing outer race is connected to the wave generator; and a stationary-shaft bearing rolling element is disposed therebetween. a portion of the stationary shaft defines a stationary-shaft bearing inner race; a stationary-shaft bearing outer race is connected to the wave generator; and a stationary-shaft bearing rolling element is disposed therebetween.