Linear actuator

A humanoid robot, comprising:

• at least one body assembly that comprises at least one body joint assembly;
• and
• at least one pair of linear actuators that form the at least one body joint, the at least one pair of linear actuators configured to operate in combination to adjust the at least one body joint assembly in two degrees of freedom through differential linear actuation, each of the linear actuators comprising:
• a motor module that comprises a motor;
• and
• a drivetrain module coupled to the motor module and comprising:
• a ball screw coupled to the motor,
• a ball nut coupled to and configured to linearly ride on the ball screw during rotation of the ball screw,
• a rod coupled to the ball nut and configured to extend or retract from the housing based on the ball nut linearly riding on the ball screw during rotation of the ball screw, and
• an anti-rotation bushing coupled to the rod and comprising at least one slot configured to engage with and linearly ride on a key coupled to an inner surface of the housing based on the ball nut linearly riding on the ball screw during rotation of the ball screw, the anti-rotation bushing further configured to restrain the rod against rotation during extension and retraction.