Low Weight and Inertia Self-Balancing Testbed for a 3U CubeSat Attitude Control System

Abstract

The design, implementation, and testing of an Attitude Control System (ACS) for nanosatellites require a simulated environment that replicates the conditions of Low Earth Orbit. Key factors such as the absence of friction and gravitational effects must be achieved in an attitude control testbed. Additionally, a platform with low weight and inertia ensures that the small actuators of a CubeSat can rotate the system without requiring excessive effort. The testbed developed at Universidad Católica San Pablo was built using lightweight materials, including 3D-printed PLA parts, carbon fiber tubes, and acrylic boards. Unlike other self-balancing testbeds, this work introduces a shifting-mass approach, where a DC motor serves as both actuator and shifting-mass, significantly reducing weight. The position of the shifting masses along their axis is controlled by a Linear Quadratic Regulator (LQR). The platform’s attitude estimation is performed using an Extended Kalman Filter (EKF), which combines data from low-cost accelerometer, gyroscope, and magnetometer sensors. A nonlinear control system is implemented for the automatic balancing procedure, mitigating gravitational disturbance torque by using the estimated gravity vector to drive the shifting masses and minimize platform tilt. Finally, a Least Squares Method (LSM) compensates for residual vertical misalignment after the balancing procedure, enabling precise center of mass (CM) control in all axes. Obtained results demonstrate the DC motor shifting-mass approach reduces total platform weight by 72% compared to other works while achieving precise balancing with less than 210 µm m residual misalignment between the center of mass (CM) and center of rotation (CR) and 92% reduction in kinetic energy variance during operation.