[Mr_I]

Leav,
In our 10 year history, we tried a telescoping pole only once: in 2004, our robot lifted a grappling hook 15' up to grab the bar. We used multiple lengths of PVC pipe of various diameters, so that each section nestled into the next, and we used cascading cabling using 600 lb test Kevlar cord (as we hadn't discovered spectra cable yet). The results are why we never used telescoping poles since.
The first stage cabling was under such high stress that it snapped repeatedly, forcing a complex restringing. We used a dual-diameter capstan pulley to pull the poles back down, since the pole was pivoted to aim for the bar, and as such we couldn't rely on gravity. We designed and built the capstans ourselves to match the geometry of the pole. We used a window motor to do the lifting and retracting.

If we ever have cause to lift again, we will hopefully never use that design again. Even though the pipe sections slid nicely, friction was a big issue. Spectra cable with (pulleys around turns!) is a must, unless you go a chain & sprocket route. And I would concur with others that draw glides are a good approach, as they are likely manufactured to higher tolerances than you can do in the shop in 6 weeks.