fischertechnik COMPUTING ROBO MOBILE SET 8 Mode D'emploi page 34

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Robots Built with
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Actuators
Sensors
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■ So how can we build a robot with our fischertechnik construction kit? To build a robot we need
sensors (e.g. pushbutton sensors,) and actuators (e.g. motors) but also many mechanical parts to
construct a model. The fischertechnik ROBO Mobile Set offers an ideal foundation for this. The following
sensors and actuators are included in this construction set:
Power Motor:
Two of these powerful DC motors (9VDC/2,4W) with built-in gearbox and a
reduction of 50:1 drive the mobile robots (this means that while the motor
performs 50 revolutions the shaft extending from the motor turns only once
during the same time.
Lens Tip Lamp:
This incandescent bulb (9VDC/150mA) enables the output of simple light signals.
A lens is integrated into the glass bulb of the lamp focusing the emitted light. By directing a beam of
light toward a light sensor (phototransistor, see below) you can build a light barrier able to differentiate
between light and dark. The lamp can also be used to display certain states or to generate warning
messages in the form of a blinking lamp. In this construction kit the lamp is used together with 2
phototransistors as special sensor for line recognition.
■ The pushbutton sensor is an example of a digital sensor. Digital values can only assume 2 different
states. These states are identified with 0 or 1 respectively. For the pushbutton sensor "0" signifies that
no current flows between the contacts, "1" signifies that current is flowing.
The fischertechnik pushbutton sensor is designed as a three-way switch. For this reason there are
three terminals. When the red button is pressed the switch connecting the terminals 1 and 3 is activated
mechanically. At the same time the connection between the terminals 1 and 2, which was connected
during the quiescent state, is interrupted. This way both possible starting positions can be selected:
Closed in quiescent state (terminal 1 and 2 connected)
Open in quiescent state (terminal 1 and 3 connected).
The phototransistor may be used both as digital as well analog sensor. In the first case it serves to
recognize clear transitions between light and dark, a marked line for example. But it is also possible to
distinguish the amount of light according to its brightness. In this case the phototransistor works as
analog sensor. Analog values can vary freely between their extreme values. These values have to be
converted into their respective numerical values in order to be processed by the computer.
Incidentally phototransistors belong to the so-called semiconductor devices, its electrical characteristics
are dependent on the intensity of the light. Everybody knows about solar cells that use sunlight to
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