We built three types of field players and goal keepers as shown in Figure 1. All robots have sturdy aluminum frames that protect the sensitive inner parts. They have a differential drive with two active wheels in the middle and are supported by two passive contact points. Two Faulhaber DC-motors allow for a maximum speed of about 1.5-2.5 m/s. The motors have an integrated 19:1 gear and an impulse generator with 16 ticks per revolution. One distinctive feature of some of our robots is a kicking device that consists of a rotating plate that can accumulate the kinetic energy produced by a small motor and release it to the ball on contact. Our smaller robots use a kicking device that is based on solenoids that can be activated faster than the rotating plate.
For local control we use C-Control units from Conrad electronics. They include a microcontroller Motorola HC05 running at 8 MHz with 8 KB EEPROM for program storage, two pulse-length modulated outputs for motor control, a RS-232 serial interface, a free running counter with timer, analog inputs, and digital I/O. The units are attached to a custom board containing a stabilized power supply, a dual-H-bridge motor driver L298, and a radio transceiver SE200 working in the 433MHz band that can be tuned to 15 channels in 100kHz steps.
The robots receive commands via a wireless serial link with a speed of 19,200 baud. The host sends 8-byte packets that include address, control bits, motor speeds, and checksum. The microcontroller decodes the packets, checks their integrity, and sets the target values for the control of the motor speeds. No attempt is made to correct transmission errors, since the packets are sent redundantly.
Our robots are powered by 8 Ni-MH rechargeable mignon batteries. To be independent from the charging state of the batteries, we implemented locally a closed loop control of the motor speeds.