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 Sunday at 09:19 PM by SNIPE

[allanp]

From the given information I shall assume that the rails will only ever be horizontal and level. It sounds like the wheels need to do two things. 1) Drive the carriage forwards and backwards and 2) support the carriage against gravity.

So could you have the top roller be the drive roller and otherwise fixed (non adjustable) and then have the remaining 3 rollers be adjustable idler rollers to clamp the varying sizes of tube and instead of using an overly complex linear actuator setup you would just used hard springs.

[SNIPE]

18 hours ago, allanp said:

From the given information I shall assume that the rails will only ever be horizontal and level. It sounds like the wheels need to do two things. 1) Drive the carriage forwards and backwards and 2) support the carriage against gravity.

So could you have the top roller be the drive roller and otherwise fixed (non adjustable) and then have the remaining 3 rollers be adjustable idler rollers to clamp the varying sizes of tube and instead of using an overly complex linear actuator setup you would just used hard springs.

I mean there's no motor, it gets moved by hand not by a motor. I suppose I could use springs after all and find another way of braking the wheels

[allanp]

Ah okay. Maybe another way could be to have one braking wheel that's non adjustable, and is braked using a beam that screws down to contact the tire via a single linear actuator or worm gear, or even an over center mechanism like you see on some industrial locking castor wheels.

Then the rest of the wheels could be made tight around the rails via hard springs as mentioned or via a single rope/string that wraps around the 4 wheel mounting arms and can be tightened.

[ord]

I think you're on the right track with the linear actuator. Springs could be a problem if you have different loads going through the carriage.

Or you could try a bunch of different wheels until you find some that are close enough (obviously you'd have to wait for the tubes for this).

Final thought (which is probably over-complicated) is looking into lathe chucks. Four-jaw chucks are capable of holding square or round tube, which can pass through the middle too.