I have managed to get hold of some very cool Rotacaster.com.au 125mm omni-directional wheels to try out. I managed to use up most of my yellow technic beams building this massive platform which will eventually house a large robot. I plan to mix it up a bit with some of the new metal parts I have been sent including some very large beautiful linear actuators.
The video below shows the platform easily moving over 12.5kg of weight using 4 XL power function motors. The wheels are a little on the heavy side compared to a normal Lego wheel however they are massively stronger and can hold over 100kg per wheel. They are 6 studs wide.
If you are interested in these wheels, please contact Rotacaster.com.au