Mud motor rotor with core and shell

A method for manufacturing a rotor for a mud motor, the method comprising forming a shell around a core, wherein:

• the shell has a different outer shape than the core, the core having a core feature arranged about the core, the core feature comprising a radially-extending ridge, wherein the radially-extending ridge comprises a circumferentially-facing leading surface and a circumferentially-facing trailing surface with respect to a direction of rotation of the shell positioned around the core, the leading surface being larger than the trailing surface, wherein the leading surface is configured to receive more torque from the shell than the trailing surface;
• the shell defines one or more lobes and one or more cavities, the one or more lobes and the one or more cavities being configured to engage a bore of a stator of the mud motor during rotation of the rotor with respect to the stator;
• and
• a thickness of the shell varies as proceeding around the rotor, from a non-zero minimum thickness to a maximum thickness.