The actions that have been determined by the control module are transmitted to the robots via a serial communication line with a speed of 9600 baud. We use radio transmitters operating on a single frequency that can be chosen between 433.0 MHz and 434.5 MHz in 100 KHz steps. The host sends commands in 8-byte packets that include address, control bits, motor speeds, and checksum. A priority value can be used to direct more packets to the most active players.
The microcontroller on the robots 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.
To be independent from the charging state of the batteries, we implemented a closed loop control of the motor speeds. 122 times per second the microcontroller counts the impulses from the motors, computes the differences to the target values and adjusts the pulse length ratio for the motor drivers accordingly.