Yes, we used identical tubing for all stages. Each of the rails fits a little loosely inside of each other - too tight and it'll bind and not move.We have small roller assemblies that hold the stages together - you can see some of them in the close up pictures, or at the top of
this picture. The roller assembly is essentially a small aluminum plate that is bolted to one of the stages, and sticks out both in front and behind the stages. Attached to it are small rollers that hold the adjacent stage in place.
If you look at the outer most stage, there is a roller bolted near the top. The middle stage (the first stage that actually moves) slides up between those rollers. Near the bottom of the middle stage, a roller is bolted on that sticks out around the outer stage - this way as the middle stage goes up, these two sets of rollers get closer together, eventually meeting at the top (if we didn't have a physical stop before then).
The inner most stage is relatively small, and has rollers bolted both to the top and the bottom of it, sticking out around the middle stage. As it goes up, there's a physical stop to keep it from leaving the middle stage at all.
We had to run a few wires with this - you can see the rollers and motors in the first picture, and they had to be powered. All the wires went up one of the tubes of the outer stage, then hung down the back through some energy chain (available in the KoP!), where they attached to the inner most stage - you can see the energy chain in the close up pictures. The wires were long enough to accommodate the entire extended height of the elevator, while the energy chain ensured they moved in a controlled fashion.
the whole contraption was built pretty well... the elevator still moves freely, and aside from cannibalized parts, the whole thing would still be working. The elevator still slides up and down extremely easily (as it must - the battery on that robot was right below it, so we have to life the whole thing up just to get it powered!).