[TEntwistle]

An additional thought - the holes in the inner side of the outer tubes looks like they are there so that the bolts holding the brackets to the poles can be tightened or a nut placed on them. It sounds crazy, but if the machine screw were placed from the inner aspect of the pole (using the access hole), if the screw hear were slightly rounded to match the internal diameter of the tube, and if the hole in the outer tube were countersunk (countersinked?), the connection could still be secure, yet allow the outer pole to slide over the inner.

I like the idea of the bracket connecting to a 2x4 or aluminum box. Perhaps it creates a field element that raises adn lowers, giving the robots a short windoe of opportunity to cross from one side of the field to the other, like the year that the robots had to cross on the tilting platform.