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DC Motors Give Foosball Robots The Winning Edge

Persistent, Fast And (Almost) Unbeatable - For Science And Software

DC micromotors with integrated motion controllers by MICROMO used in tabletop soccer robotWhat looks like a toy is actually a science experiment with a significant potential for research as well as retail. Unfortunately, the merits of such work are often underestimated, particularly in Germany. One of the exceptions to this is a research project conducted by the University of Freiburg in cooperation with Gauselmann GmbH, a subsidiary of the Gauselmann Group. Within the framework of a doctoral thesis by Thilo Weigel, the team developed a special piece of software for foosball, table soccer. It is designed to react intelligently to situational moves that are made in the game. Modern processor technology and optical image processing via cameras are deployed for data input and evaluation. Durable, high-speed dc motors perform as actuators. This "game" creates the perfect basis for testing, "situational" software. The commercial success as a table soccer robot is an added bonus of these research activities.

A Camera Captures all Ball Movement to Control Players via MicromotorsA theory is only good if it also works in practice. With this in mind, the chair for artificial intelligence at the University of Freiburg chose an "interactive" approach when it came to developing its new software that reacts to different situations. The practical test provides valuable information regarding possibilities for improvement. One of the essential prerequisites is a complex situation that also demands quick reactions from the program. A glance "outside the box" quickly shows that there are best-in-class solutions even for such apparently challenging cases. A table soccer game is highly demanding due to its complex play pattern and also because of the high speed of the ball. A controller that can get to grips with this specific problem using the appropriate actuators is also capable of mastering other automated tasks.

Everything that happens in the table soccer robot occurs in an area ­measuring just 220 x 157 x 121 cm (height, width, depth). Given the complexity of the ­operation, this can be considered a ­comparatively compact testing device. The chair for artificial intelligence worked with specialists in the field in order to come up with the best possible strategy. Micro motor expert, FAULHABER contributed its drive know-how to ensure the required shooting power and ­mobility of the unit, while adp Gauselmann GmbH, renowned as a high-end manufacturer of gaming equipment, was responsible for the practical configuration of the robot.

Functional Principle

An Infrared camera detects the movement of the ball to direct the positioning of the bar and "players"A PC computer provides the actual control of the game. An attached camera delivers the necessary data of everything that's happening on the playing field. The PC software evaluates the current camera image every 20 milliseconds. In doing so, it determines the ball position as well as the velocity of the ball. Using this data, the program then decides when and how a particular player should be moved. This results in the bar or bars being re-positioned horizontally, and thus the players, being rotated. Thus, the ball can be struck successfully by the players or parried by the goalkeeper.

One of the prime objectives is to handle as little data as possible in order to enhance the actual evaluation process. State of the art data-capture and work distribution are essential. An infrared camera observes everything that is happening from below through the transparent playing field. A "floodlight" with approximately 300 infrared light emitting diodes on the border illuminates the playing field. The playing surface itself is covered with an infrared-permeable filter film, so that only the infrared rays reflected by the ball are detected by the camera. This facilitates the evaluation process when registering the ball.

The stream of data to the actuators is also minimized. Here, the controller PC only issues superordinate commands such as: "right", "left" or "shoot"; the actual fine-tuning is performed by ­subordinated control units. The table soccer robot uses standard FAULHABER Motion Controllers for this purpose. The game is brought to life thanks to minimal computing times, which in turn are a result of the stream-lined data set and the reduced delay times.

High-Speed Drive with Cable and Belt MechanismPlayer Drive

In contrast to professional soccer, the Star Kick Robot is capable of "motivating" its players without the lure of mega salaries. All it takes is two motors for each bar. Drives positioned on the base plate of the device move the players horizontally via cable pulls in the bars. The cable is looped around the respective driving drum several times and is prevented from slipping through as a result of increased friction. This ensures an accurate, synchronous control of the players. The developers used a belt drive on the rear of the device to control the shooting power, e.g. the rotation of the players. The motors have to move very dynamically in this application, but only ever for a brief moment. The Schönaich-based drive specialist therefore recommended the use of quick-running standard coreless dc motors with carbon brushes. These durable motors can reach a peak power output of over 220 Watts, which means that they have more than enough power for the players.

DC Micromotor and Motion Controller Provide Fast and Accurate PositioningEach driving motor has a magnetic ­pulse generator to communicate the respective player positions to the ­controller. At 512 pulses per revolution, the resolution is so fine that no ball can evade the players’ feet. A motion controller provides the actual control of the motor and angular momentum processing. At the start of play it drives the players into a defined starting position and then evaluates the speed sensor data. The data processed in this way is sent to the PC via an RS232 interface. This then responds by issuing the information for the control of the players. The controller then converts this into electrical impulses for the motor. Cable or belt sheaves provide the correct reduction during play. Taking into account the required acceleration values, the transmission is designed in such a way that ensures the motors operate within the optimal speed range. Combining tailor-made design and high-performance drive technology, the specialists involved in the project have been able to deliver solutions which were considered impossible just a few years ago. Indeed, today even the highly efficient range of standard products available within the area of micro-drives is capable of mastering complex tasks. All it takes is creativity and skill – and state of the art drive systems providing the necessary momentum.

To read more about how dc motors from FAULHABER and MICROMO are used in Robotic Applications, visit our case study page.