pic: Piston-in-Tube Concept

I’ve noticed a lack of stuff-in-tube mania on CD lately, so I thought I’d fix that. :stuck_out_tongue:

More pictures: http://imgur.com/gallery/EmCRX

This is a 3/4" bore cylinder sitting inside a 1x1x1/16 square tube, but the concept could be applied to larger tubes and larger cylinders. At least until the cylinder gets so big, there’s no point to protecting the piston rod anymore. This is the only way I could think of to do linear motion without a separate support bars and a more complex superstructure. There’s probably an easier way to achieve linear motion out there though.

I put a lot of rollers cause I’m not really sure how many I need. Do I have too many? too few? I hope it’s too many; I made a less-than-CAD prototype of this with what I had on hand, hoping to put it on our Stronghold robot if it works well.

(Someone’s probably going to scold me for calling cylinders pistons, but cylinder-in-tube just doesn’t have the same ring to it. :smiley: )

Team 5830 did something similar for their climber last year, though not including the protection for the stroke (obviously, given the dimensions). It is nice how neatly these cylinders fit in such tubing.

Rather than using bearings, what’s keeping you from using a short section of tube of the next size up, and possibly applying a thin sheet of delrin or HDPE as a bearing surface?

Some clever material selection here could eliminate the bearings entirely, while still providing the same effect.

I’d be a little leery of only using two bearing sets if straightness was critical (it often is), and would suggest 3-4 sets (2 on one side, 1-2 on the other) in such applications. Or, as noted, some clever material selection.

We did something like this back in 2011, but only the cylinder was in the tube, not the piston rod. Rather than using bearings we used linear slide rails on the mechanism it was actuating. Worked pretty good, and definitely saved space.

Isn’t a pneumatic cylinder on its own already a piston-in-tube device?
You could shave some weight off if you used a bracket to secure a tube to the nose of the cylinder so that only the piston rod is enclosed. You might need to rethink mounting, but the weight saved would be non-negligible. In addition, it could be argued that such a design would be more faithful to the name.

We did something similar with Delrin tubes and bars for our 2013 climber (underside, CAD shot). No rollers since the Delrin slides. It ended up being a good way to steamline the package for the pyramid skids. Be ready to demonstrate to the inspectors that you haven’t modified the cylinders, however. Some RIs will pay close attention to any pneumatics they can’t clearly see. (We showed them a spare.)

Generally, in my experience, these kinds of things are more for saving space than weight. Square tube is also much easier to mount things to.

Any weight that can be shaved off is more weight for future improvements. Furthermore, if you wanted to place the mount near the nose of the cylinder anyway, the method I proposed would not present any impediment.