Rollers for variable diameter tubing

[SNIPE]

Hi,

What would the best mechanism be to have rollers that wrap around tubing that can be up to (lets say, 1 inch squared) it can be square or round in cross-section.

Since I'm not sure what the diameter will be yet until it arrives, I will make the mechanism adjustable, but also the bottom tubing is round i cross section and narrower than the top tubing, which is square in cross section.

Here is how the layout will be anyhow, c stands for carriage:

I made a simple lever and linear actuator mechanism but forgot to have just a single wheel then a beam on both sides.

Since the carriages are heavy and hang off the sides of the tubes I'm not sure if just these rollers will work, I think I need rollers for 2 or 3 sides of each tube.

I could also have something like this:

But instead claw panels its rollers and instead of actuators I could have worm gears, but that would imply its a central worm gear/actuator that drives all 4 claws, but the tubing will be in the way there, so you would need 4 worm gears/actuators on each corner of the tube - over-complicated.

This would be WAY easier if LEGO made springs that expand instead of compress, rubber bands are too unreliable.

Here is a real 4 sided roller around some square tubing, these use 2 rollers per side which I probably don't need:

Edited 3 hours ago by SNIPE