Mini footballers run on dc micromotors

Oct. 20, 2005
As flesh-and-blood footballers took the field at the European Soccer Championship, their nonhuman counterparts kicked off a game of their own at the Robot Football World Championship in Portugal.

Shootout at RC (Robocup) corral.


A robotic fielder feels the electricity as it waits the start of action.


Robot football is divided into several categories: small, midsized, four-legged, and humanoid. A German team built and managed by the computing faculty from FU Berlin placed first in the small-size category. Their strong performance depended on batteries and small robust dc-micromotors.

The robots play on a field measuring 4.90 3.40 m. The ball weighs 46 gm with a diameter of 43 mm. The robotic players must fit in a cylinder 180 mm in diameter and not exceed 225 mm in height.

As in traditional soccer, there are two halves to each match and a 10-min break in between. There are yellow and red cards for pushing, and substitutions in the event of "injuries."

A team consists of four field players and a goalkeeper. A colored badge identifies the team and further markings identify individual players. The robots can navigate independently or be controlled via an external vision computer and radio. Human intervention is allowed only for introduction or removal of players. The ball, which moves up to 12 mps (about 45 km/hr) is kicked via an electromagnet with a "kicking stick."

Precious-metal commuted dc micromotors from Faulhaber Group, Switzerland, drive the robots' four omnidirectional wheels. Switching off the appropriate motor changes the robot's direction.

The motors with integrated encoder work with matching metal planetary gearheads. The field players, which must quickly cover larger distances, have a smaller gear reduction (14:1) than the goalkeeper (19:1). Despite the small playing field and a weight of 1.8 kg, the robots travel 3 to 4 m/sec. The motors operate at 10 V, instead of the standard 6.

To avoid pushing, the robots must be able to brake quickly. As a result, the motors are subject to a short-term countervoltage up to 20 V. Despite the overload, the motors have operated problem-free for four years, i.e., several hundred operating hours.

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