[Al Skierkiewicz]

Acer,
An extension for 6-7 meters would need some serious counter balance or a support at the end to hold up the extensions. How much stess will the device receive from the blocking action? Will the opposing robot be able to crash against your device? If the answer is yes, you might want to come up with a different strategy.
As to telescoping assemblies, Small Parts sells tubing that nests inside the next larger tube, but they are not long enough for the 6-7 meter dimension. On our robot lasst year, we used some drawer slides from McMaster Carr. They were heavy but allowed us to have and extension that went up to about 5 meters vertically with a 2 meter height when collapsed.