A robot leg assembly including a hip joint and an upper leg member. A proximal end portion of the upper leg member rotatably coupled to the hip joint. The robot leg assembly including a knee joint rotatably coupled to a distal end portion of the upper leg member, a lower leg member rotatably coupled to the knee joint, a linear actuator disposed on the upper leg member and defining a motion axis, and a motor coupled to the linear actuator and a linkage coupled to the translation stage and to the lower leg member. The linear actuator includes a translation stage moveable along the motion axis to translate rotational motion of the motor to linear motion of the translation stage along the motion axis, which moves the linkage to rotate the lower leg member relative to the upper leg member at the knee joint.