Using the Java applet on the right you can pick out the differnet components of the ClimbBot

Arm One and Two use the Drive Wheels along with the Drive Axel to move up and down as well as forward andbackwards.
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).

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Here you can see all
around ClimbBot and the
arms in motion.
gif 17 frames (297k)

MORE images of climb Bot

Source code for the above Java applet can be found here