Top performance by DC-motors
As the football stars took to the field at the European Championship in Portugal, their non-human counterparts kicked off at the Robot Football World Championship. Even without the excitement of live broadcasts during peak viewing time, the "players" and teams gave an admirable performance. The robot team with managers from the Computing Faculty of FU Berlin accomplished great things. The players' strong sprinting and running performance was accomplished with batteries and small robust DC-motors.
Robot football is divided into several categories: small and mid-sized, 4-legged and humanoid. Germany won the title in the small-size category. For the robots, this meant a playing field with dimensions of 4.90 m x 3.40 m. The ball weighs 46 g and has a diameter of 43 mm. The players have to fit into a cylinder of 180 mm diameter, with a maximum height of 225 mm. As is the case with traditional football, there are two halves to each match and a break of 10 minutes in between. The rules include yellow and red cards for pushing, as well as substitutions in the event of "injuries".
Together we are strong
The team consists of four field players and a goalkeeper. According to regulations, a yellow and a blue team always compete against each other (further information from www.robocup.org). The "strip" is a coloured badge 50 mm in diameter in the centre of the robot's upper side. There are also further markings, e.g. to identify the individual players. Depending on the system, the robots can navigate independently, or be controlled via an external vision computer and radio. The playing field is recorded from above by camera. Human interventions are not allowed, only introduction to or removal from the playing field is permitted.
The action of kicking the ball via an electromagnet with a "kicking stick" is also computer-controlled. The ball achieves speeds of up to 12 m/s, i.e. approx. 45 km/h, thanks to the capacitor discharge into the coil. Therefore, nippy goalkeepers are simply a must. Given these challenging conditions, it would appear obvious that customised solutions are the only choice if one is to succeed. The FU Berlin team therefore built its team from individual components.
The manager, Professor Raúl Rojas, commented: "The system is only as stable as each individual component. For this reason, we as developers concentrated on a simple but sturdy design. Potentially, any individual part may fail – thus increasing the probability of failure of the entire team." For robots too, the maxim applies: He who wishes to win must first reach the finishing-line. The system, consisting of an external control computer, wireless data transmission to the internal robot electronics and a drive mechanism is still very complex. The success of the team at the RoboCup bears testimony to the ingenuity of its design. After three runner-up world championship positions, the much sought-after title has finally been attained.
Sprinters and dribblers
The robots are driven by four omni-directional wheels; each wheel has a series of smaller wheels distributed over the perimeter transverse to the direction of travel.
The advantage of this arrangement is the possibility of direct control. As each of the four wheels is driven by its own motor, to change direction, the appropriate motor is simply switched off. The robot then travels linearly in the desired direction "via" the small wheels of the drive-less wheel. "Curves", as with car steering are thus not required, and manoeuvrability is increased, even in the most restricted spaces. As the drive source, the experts use precious metal-commuted DC-motors developed by FAULHABER. The motors in the 2224 SR series with integrated IE2 pulse generator (64 pulses/revolution) are used with matching 20/1 metal planetary gearheads. The compact unit eliminates the need for further components and allows high-precision control. As the field players must quickly cover larger distances, they have a smaller gear reduction, at 14:1, than the nippier goalkeeper with 19:1. Thus, despite the small playing field, the robots reach speeds of 3 to 4 m/s, with a weight of 1.8 kg. Naturally, this performance cannot be achieved with the conventional operating specifications. Instead of the standard operating voltage of 6 V, the motors are operated at 10 V.
In order to avoid pushing, the robots must be able to brake quickly. As a result, the motors are subject to a short-term counter-voltage of up to 20 V. Despite this "overload", the motors in the robots have operated problem-free for four years, i.e. several hundred operating hours. Demagnetisation, bearing damage, carbon consumption or unsoldering of the armature coil on the collectorproblems that may occur in low-budget drives developed by other companies – are simply not an issue with the "souped-up" FAULHABER solution. The micromotor’s "fitness" level is world class, as one would expect from a champion. Boasting impressive performance in a small footprint, FAULHABER micromotors are the perfect choice for a range of applications – even those that are slightly more "unusual". Many years of experience, combined with state-of-the-art materials, are the basis for outstanding results. Perfectly synchronised pulse generators and gearheads are an advantage not only in robot football but also in industrial applications, an area in which compact design and performance are often essential. The highly reliable and durable components also reduce operating and maintenance costs – the perfect solution for applications that require maximum efficiency until the final whistle has been blown.
The Robocup Federation