Battery Powered Trolley
In 2006, LEGO will release 9V battery powered trains. Here is
a 9v battery powered trolley I bult around 1998. It can run
on 9v metal track or 4.5v gray track. The trolley
automatically reverses when it reaches a stop block (a 2x2 tile, on top
of a 2x2 plate, attached to the middle of the track). I
technic axle hangs down and is connected, through a connecting link to
the arm on a 9v polarity reversing switch. When the trolley
hits the stop bloc, the polarity switch is turned, polarity reversed to
the motor and the trolley reverses direction. This trolley
uses the larger, 9v motor for the wheels.
At the time this was built, green bricks were considered very rare.