The pendulum was built using parts of a dot matrix printer. The step motor (originally present on the printer) Was replaced by a DC motor, also reused. Two end switches were placed as a safety measure for the equipment. The angle of the pendulum is measured by an incremental encoder and a the position of the car (consequently the speed of the motor shaft)is obtained through an optical position sensor.
The controller used was a LQR (Linear Quadratic Regulator) with an integrator inserted to allow the cart to tracking a reference. Thus, the controller can make it go a desired position while balancing the pendulum.
The swing-up algorithm used was proposed by the laboratory to raise the pendulum with small movements of the car (because the excursion of the prototype is quite limited), when the pendulum comes close to the equilibrium point the LQR control is switched on.
The proposed algorithm and more details about the work can be found at this Article