ClimbBot

Arm One and Two use the Drive Wheels along with the Drive Axel to move up and down as well as forward and backwards.
This motion (simular to a steam engines piston) in each arm, drives the 'hand over hand' locamotion alowing the robot to 'climb' along a cable.

The Lego RCX brick simply runs both motors at a constant speed.
When the bumpers are connected to the Sensor Array impacts with objects set the motors on reverse.

If the Drive Axel is removed then the Arms move indepentently of each other and we easly loose the 'hand over hand' action, leaving us with a 'pull up' action (useless).