One of the most important problems of mobile robot platforms is associated with the power supply. With exception of some special systems, batteries, dry or rechargeable, are the most commonly seen sources of electrical power in robots. The power supply system of zBot’ consists of two parts, the main accumulator and the auxiliary battery. The main power source was realised with a NiCd or NiMH bat-tery pack. Its size was adapted to fit the battery holder of the Tamya chassis (six 1.2V/1400 mAh C cells). The main power is activated for DC motor driving and for the servos.
The auxiliary system, two Alkaline AAA batteries, is for the power supply of the microcontroller only. A third (optional) power source is the solar panel. It is not really necessary for initial experiments but it helps to keep the robot autonomous longer. The drcuit of zBot’s main power supply sys-tem indudes a special feature the charge control circuit based around a MAX472. For effective operation, we have to know the exact capacity of the battery. Imagining the discharge voltage diagram, we know that the voltage is virtually stable for most of the discharge time and suddenly breaks down when the battery runs out of capacity. This time is very short, so it could happen that the robot could be lost. A simple voltage control doesn’t give us the information we need.
The only way to obtain exact values is monitoring the discharging. The MAX472 gives two values, the current through R24//R26 as a proportional voltage at pin 8, and the current direction through the resistors (SIGN). Both values allow cal-culation of the charging (solar panel) or dis-charging of the battery pack The auxilliary power is shown in the CPU unit. The two alkaline batteries support the CPU, the wireless radio modem and the navigation system (compass) only. The reason for the division of the power supply is simple. With the help of the auxiliary system, zBot communicates with the operator wirelessly. In this way, the inde-pendent power source increases the secu-rity of the system.