The stability and balance of humanoid robots, particularly during locomotion in challenging environments such as stair climbing, navigating uneven terrains, and responding to external disturbances, present significant challenges for their practical application. This thesis aims to address these challenges by redesigning the waist joint of humanoid robots using a combination of an MPU6050 gyro sensor, a mechanical gyroscope, and gyroscopic reactive coupling to maintain stability while standing, walking, and running in unstructured and unpredictable environments. The design parameters for the gyroscopic disc, including radius and thickness, as well as the inner and outer gimbals were established. A Linear Quadratic Regulator controller was designed, alongside an Arduino Uno board to serve as the control system. The gyroscopic device mounted on the humanoid robot‟s waist, was modeled using SOLIDWORKS and demonstrated to counteract disturbances that may lead to instability, particularly in the sagittal plane where the risk of falling was found to be higher. Aluminum alloy (AL-7075-T6) was selected for the gimbals and flywheel (disc), while brushless DC motors were employed to drive the gyroscopic disc. The system was designed for humanoid robots weighing 76.4 kg and standing 1.74 meters tall, generating a gyroscopic couple of 99.947 Nm at a disc rotation speed of 350 rad/sec. For this design, a factor of safety of 4.6 was established, ensuring optimal protection and reliability. The balance control system was evaluated in three orientations (roll, pitch, and yaw) based on the linearized dynamic equations of the system. Simulations were performed in MATLAB, demonstrating that the system improved stability across various disturbances and angular inputs. With an average rise time of 0.30 seconds and a minimal overshoot of just 0.69%, the system, on average, reached peak responsiveness in 0.53 seconds and achieved full stability after 3.50 seconds, demonstrating the Linear Quadratic Regulator controller's precise control and low oscillation. This study improving performance of humanoid robots in unstructured environments and it meet the growing market demand. Keywords: humanoid robot waist, gyroscope, linear quadratic regulator, stability and balance.