When you need a LEGO robot attachment to lift heavy things on the competition field. Probably at FIRST LEGO League or World Robotics Olympiad. This attachment uses 4-5 gear wheels to lift a heavy object.
Build with LEGO Mindstorms EV3 parts.
Building instructions for a robot for the World Robotics Olympiad Sputnik competition. This is the light version without the lift at the top.
For the FIRST LEGO League 2016-2017 Animal Allies we prepared an attachment for lifting the robot. The idea of the attachment is to show how you could lift the whole robot with a system of gear wheels, levers, and scissors constructions.
Built mainly from LEGO Mindstorms EV3 parts but could probably be constructed from NXT sets.
This construction demonstrates one way of using а rack with a gear wheel. It allows to turn circular motion in to a liniar one.