Variobot varikabi Manual page 69

Transistors
Since varikabi's drive motors require a much higher current than the
sensors can supply, amplifiers are needed. A transistor is a simple
three-terminal electronic amplifier.
To make sure that the gain is sufficiently high, so-called Darlington
transistors are used, which already contain two series-connected
transistors.
The right and left motors require equivalent transistors, a so-called
PNP and an NPN transistor. They can be distinguished by their
imprint BC516 (PNP) or BC517 (NPN).
Bend the outer two legs slightly apart so that the transistors fit well
into the breadboard. Then insert them into the breadboard according
to the illustration on the left and right of the resistor.
Caution:
The two transistors BC516 and BC517 must not be mixed-up and
must be inserted turned differently.