Ball scale
Experimental setup for control engineering laboratory

The ball scale is a fascinating teaching model that vividly conveys the principles of control engineering. With a specially developed function block editor, students can independently design and optimize control loops. The goal is to control the tilt of the seesaw via a propeller drive so precisely that a metal ball is stably balanced in the center.

At the center of the control track is a propeller drive connected to a pivot-mounted V-profile. A ball can roll freely on this. A servo motor changes the angle of attack of the rotor blades to specifically generate thrust to the left or right and thus change the tilt of the seesaw.

The challenge is to develop a control loop that manages the highly dynamic and unstable system so that the rolling ball comes to a stop in the center of the V-profile. Even the slightest changes in tilt set the ball in motion. The weight of the ball acts as a disturbance, as does the varying propeller speed and turbulence of the airflow. These factors significantly increase the complexity of achieving stable control.

For control, the ball position and the tilt angle of the seesaw are available as measurement variables. A pitch-adjustable propeller must suffice as the only actuator to keep the ball in balance.

A specially developed function block editor is available for creating a controller. The editor, programmed in VB.NET, includes all common control elements, such as PIDT1 controllers, and can be flexibly extended with user-defined function blocks. A special feature is the ability to edit the entire signal course during runtime. Changes take effect immediately, without the need for recompilation as required in MATLAB Simulink.

The ball scale represents a complex, nonlinear control system. The developed control loop includes a total of four cascades with five PIDT1 controllers, which influence the state variables of speed and position of both the ball and the lever. Each cascade stage is finely tuned to reliably keep the ball in the center despite unstable conditions.

To better understand the complexity, the experimental setup can optionally be controlled manually via a joystick. This quickly makes it clear how challenging or nearly impossible it is to keep the ball balanced without a sophisticated control system.

All mechanical components were designed in AutoCAD and manufactured on a CNC milling machine. This allowed for high precision and reliability in implementation.

For programming the function block editor in VB.NET, Visual Studio was used, while for microcontroller programming in C++, the ATMEL AVR Studio was employed. Additionally, HTerm was used to monitor the serial communication between the microcontroller and the PC during development.

The THWS (Technical University of Würzburg-Schweinfurt) has taken over the experimental setup 'Ball Scale' for its Control Engineering Laboratory. Prof. Dr. Abid Ali, who leads the lab, expressed his heartfelt thanks for the extraordinary commitment.

The person who takes on the challenge and succeeds in developing a controller that precisely stabilizes the ball in the specified position will be awarded a certificate and a prize from Engineer Glaser. 🙂

Many thanks to Prof. Dr. Ali for the thorough imparting of valuable control engineering tools during my studies. The practical and in-depth exercises complementing the lectures have provided me with a solid foundation that continues to play a central role in my engineering work and significantly contributes to my understanding of complex technical systems.