This picture shows teams 2468, 456, and 1421 triple balancing on the practice course at the Dallas West regional.
This balance was done (several times) following the rules of a normal match. We did not simply place the robots this way and take the picture. We had team 456 get onto the bridge first with 1421 behind them. Once the two of them were balanced, 456 turned sideways. The bridge was then tipped toward us (2468). With our strong drive and traction due to our pneumatic wheels, we were able to push both robots up the bridge rather smoothly.
This also happened without the help of a stinger or any such device (which we have since added)
As for a basic description of our robot, we use 8" pneumatic wheels which are great for going over the barrier, but alos provide excellent traction for pushing other robots both for defense as well as balancing. The "cannon" as we refer to it is a 100% student designed and built apparatus. It can both pick up balls and shoot them fairly accurately.