in 1990, LEGO introduced a second line of motors, running
at 9V on six AA batteries (shown in Figure 12-1). These
motors are considerably more powerful and convenient to
use than their predecessors. The 9V line also has greater
variation, including motors for boats with propellers and
watertight housings. The 9V motors are widely available
and highly popular. We’ll discuss this line of motors in this
chapter, with the exception of some specialized ones, such
as the Trains and Monorail motors, which are very difficult
(or downright impossible) to use outside their intended
applications