A standard metal tape measure has a slight transverse curve to it when unrolled, so that it has a certain rigidity and can hold itself straight against gravity. When it gets retracted back into the body of the tape measure, that curve gets flattened out so that the tape can roll smoothly around a spool inside the case without kinking. In fact, when the transverse curve is flattened out, the metal tape spontaneously curls up lengthwise.
The amount of transverse curve built into the tape strikes a balance between offering enough rigidity and keeping the edges of the tape close to the underlying surface so that accurate measurements can be made.
But what if we added more transverse curve to the tape? Could we have the tape come out and form a transverse semicircle? Could you have the tape edges overlap, spontaneously forming a (not sealed) tube as the tape comes off the reel? You could then ‘unzip’ the tube back into a reel of flat tape.
Depending on the material, you can only bend it so far before it loses it’s ability to go back to it’s ‘original’ shape.
Seamless gutter machines will bend lengths of sheet metal (which is basically what a tape measure is) into just about any shape you want. On the one hand, they won’t go back to flat…OTOH, they would go back to being flat if you ran them backwards through the bending machine (or maybe a different bending machine designed to take the creases out).
Having said that, I don’t see why you couldn’t come up with a grade, thickness and width of steel (possibly more than one layer welded together at the edges), that would bend into a circle when laid out and be flat when wound up. However, I have a feeling it would be fairly stiff and take more than a pre/auto loaded spring to wind it back up.
Rather famously, the original and first replacement solar arrays on the Hubble Space telescope (and thus one might expect a lot of other spacecraft) used a version of what you describe to create the struts that held the solar panels. Famously, the design caused a problem, that although not as severe as the optical problems, still created a very significant issue. The two sides of the strut would heat differentially in the sun, and as the HST orbited the Earth this differential heating would change from one side to the other. This caused a slight change in length which made the struts curve, and flap every orbit. And the flap took ages to damp down. This was enough to create major headaches in pointing the craft. The first HST service mission replaced the panels with identical ones - but with insulation around the struts. A later mission replaced those with high performance gallium arsenide panels with no flappy struts (same as the NRO sats had always had.)
Thanks, Francis Vaughan! The Storable Tubular Extendable Member is exactly the kind of thing I was thinking of! It’s impressive that there are versions that can push with 150 lb of force.
While we’re at it about spacecraft, tape measures are also used for antennae on satellites. As in, literally tape measures. They buy them off-the-shelf from the same companies that make them for carpenters (though I think they arrange to buy them before they get the inch markings painted on). All that the satellite maker has to do is reverse the spring on the coil (so they spring out instead of springing in) and put something on the end to keep it from springing out early (like a thin wire that can be burned out like a fuse, when they want it to deploy).
Oh, and what’s so implausible about the name? It’s a description of the thing, and it’s similar to a stem, so the acronym works in both ways. Yes, yes, it can be interpreted phallicly, but that’d be an issue no matter what they called it, because no matter what you call it, it’s still basically a rod shape.
Actually, since you mention the natural (nature-al) suggestion of extensible members of all kinds, in seeing thread title I first thought of molecular (textural protein generation) or cellular dynamics of extending and compacting volume in sea organisms.
Not metal, but you might be interested in pipe conveyors. They’re flat for loading/unloading like a standard conveyor belt, but then they roll up into a pipe shape to combat spillage, dust, contamination, etc.
As a retired NASA engineer and collector of measuring tools, I can add a couple of interesting insights. At Glenn Research Center we worked on the original solar arrays for the ISS. They used the coiled, self building mast as mentioned. The one we used was called an “Astromast”, although when I Google that term the mechanism looks different then I remember.
As for the tape measure itself, that thin coiled blade design was the work of Hiram Farrand, and the Farrand Rapid Rule was described as a “concave-convex, flexible-rigid rule”.
I have several of them, and they are a marvel to use. Note that they used the housing merely to hold the rule, it was removed completely in use. The Farrand was coiled “inside-out” and pulled from the center, not the periphery. Pulled was the wrong term, you did not have to pull it, it was self driven, without any springs, just the rule itself. Those two handles are gripped between the thumb and forefinger and squeezed together (after the rule was pulled out a few inches), at that point the friction lock would release and rule would straighten and eject itself with considerable velocity. An unaware user can easily stab his eye.
I once managed to shoot the rule across a room and embed it into a wall!
(Reminder to self: make a video for Youtube)
Even when the first manufacturers changed it around to pull out the way we are used to, it was still removed to use. Stanley Rule advertised this version as the Stanley Safety Rule, since the eyes of everyone in the room were safe! When they finally attached it to the axle, it was called the “Push-Pull” rule.
I used to have an 18 inch metal ruler that was the same idea as a Rapid Rule or modern tape measure but minus the container. It was just a coil of metal that you could unroll flat then it’d snap into its rigid shape.
The only downside while using it was it was kinda easy to push on it wrong and flatten a spot. At which point it would spontaneously coil itself up like a giant pillbug. Usually whacking your fingers pretty good in the process, or grabbing your pencil out of your hand and flinging it across the room. Such fun.
There’s also these things: Amazon.com : slap bracelet which were all the rage with kids a few years ago. And may still be for all I know.
