http://www.cyberblue234.com/images/p...04/robot/3.jpg
This is a link to our 2004 robot. It had heavy duty tank treads. The treads gripped the edge of the platform and pulled the robot up.
These were functionally good, but very heavy and required a special drive "cog" on the inner tread.
However, they were practically indestructable - they had a kevlar layer in them and we actually designed for bomb finding robots.
Several other robots used similar designs of treads to make the step up.