Ball Balance
Experimental setup for control engineering lab

The ball balance is a fascinating teaching model that clearly demonstrates the principles of control engineering. With a function block editor developed specifically for this purpose, students can design and optimize control loops independently. 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 plant is a propeller drive connected to a rotatably mounted V-profile. A ball can roll freely on this. A servo motor changes the pitch angle of the rotor blades to deliberately generate thrust to the left or right and thus change the tilt of the seesaw.

The challenge is to develop a control loop that controls the highly dynamic and unstable system so that the rolling ball comes to rest in the middle of the V-profile. Even the slightest changes in tilt set the ball in motion. The ball's own weight acts as a disturbance just like the varying propeller speed and airflow turbulence. These factors significantly increase the complexity of a stable control.

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

A specially developed function block editor is available for creating a controller for this setup. 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 flow during runtime. Changes take effect immediately without needing to recompile as is required with, for example, MATLAB Simulink.

The ball balance represents a complex, nonlinear control system. The developed control loop comprises a total of four cascades with five PIDT1 controllers, which act on the state variables of velocity and position of both the ball and the seesaw. Each cascade stage is finely tuned to reliably keep the ball centered despite the unstable conditions.

For a better understanding of the complexity, the experimental setup can optionally be controlled manually with a joystick. This quickly makes clear how demanding or nearly impossible it is to keep the ball balanced without an elaborate controller.

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

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

The THWS (University of Applied Sciences Würzburg-Schweinfurt) took over the “Ball Balance” experimental setup for its control engineering lab. Prof. Dr. Abid Ali, who leads the lab, expressed his sincere thanks for the outstanding commitment.

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

Many thanks to Prof. Dr. Ali for the solid teaching of valuable control engineering tools during my studies. The hands-on and in-depth exercises complementary to the lectures provided me with a solid foundation that continues to play a central role in my engineering work today and has significantly contributed to my understanding of complex technical systems.