5 ms·
Two words: zip tie.
by kghose 14y ago
Two words: zip tie.
- sosuke 14y agoPerhaps zip ties can't withstand the changes in pressures or heat. Expansion, contraction, and all that mess. I'm simply arm chair guessing here.
- skorgu 14y agoThe link itself addresses this: Overtightening of cable management bindings can cause conductor breakage, insulation damage, excessive chafing, and deformations between the conductive, dielectric, and shield parts of a cable, and no doubt a host of other issues. It is one of the classic problems with ratcheting plastic cable ties (i.e. "zipties") that they only have quantized adjustment steps and cannot be easily loosened. While zipties with a metal tooth insert do allow for smoother tightening, the possibility of this tiny metal part coming loose near electronics generally excludes their use. That zipties cannot easily be loosened or adjusted during tightening makes them more prone to being left in an overtightened state. Difficulty of adjustment might also be considered a possible strike against using the Constrictor Knot (and similar knots) for this application.
- kghose 14y agoI'm not convinced by this explanation. A skilled person will do fine with a zip tie. Knots once tied should not be easy to untie in such applications - you don't want possibility of failure. An over tightened zip tie can be quickly cut away. The thing that seems reasonable to me is lacing works for thin cabling, but if you have a fat bundle of cables (say 5mm or more in diameter) I can't really see a big problem for zip ties.
- jahg 14y agoLacing is lighter, and mass matters.
- deleted 14y ago[deleted]
- biot 14y agoHave you considered consulting for NASA? They've likely put no thought into materials selection and I'm sure they'd benefit from your vast experience in the performance of zip ties in non-terran environments.
- oasisbob 14y agoIt's not just NASA, zip-ties are banned in plenty of data centers and telecom facilities for the reasons cited. Less of a concern on Mars, but the edge where the excess is cut away can be really sharp and hazardous as well.
- stevenrace 14y agoIn the Aerospace industry, special applicator guns exist to zip bundles of wire in a specified tension. [1] But the use of butchers twine and wax line in still rather common. A few more points: - Zip ties are also made of ABS plastic - which has a Tg of <200*F...things start uncoupling around there. - Kapton gets brittle, and most of these cable bundles are covered in the stuff. - Mass. There are plenty of lightweight fibers (Aramid/Kevlar, carbonfiber, nanofibers, etc) whose tensile strength is greater than steel. - Lastly, I'm biased against zip ties after multiple recabling projects while in IT... [1] http://tools.tycoelectronics.com/cabletiegun.html http://tools.tycoelectronics.com/cabletiegun.html
- rhizome 14y agoSince there are no skilled persons on Mars, they have to do better than "fine."
- damoncali 14y agoThe thermal extremes of space are severe, and can easily render a simple zip tie to be useless. Another issue is the potential for materials (plastics are a particular headache) to offgass in a vacuum, which can send nasty contamination into places that it shouldn't be (like sensitive instruments). They actually test these components in vacuum chambers while thermally cycling the assemblies to figure this out.
- kghose 14y agoWell, neither wikipedia nor the linked article say why zip ties aren't used. I don't know what material the lacing is made from, but unless it is a natural thread I'm sure zip ties can be made from that material. It might be that tension (which is what I worry about when I zip tie delicate things like optic fibre) is better controlled in hand tied knots, but zip ties can be tied pretty precisely.
- ars 14y ago"but unless it is a natural thread I'm sure zip ties can be made from that material" A zip tie requires a different combination of compression strength, tensile strength, and elongation stability compared with lacing. So the materials are not interchangeable. Also, individual fibers bundled into a cable is MUCH MUCH stronger than the exact same amount of material as a single homogeneous cable. And individual fibers can handle flexing and vibration far far better than a single large strand.
- ChuckMcM 14y agoSee this: http://code541.gsfc.nasa.gov/Uploads_materials_tips_PDFs/TIP%20012R.pdf http://code541.gsfc.nasa.gov/Uploads_materials_tips_PDFs/TIP... for acceptable lacing materials. Zip ties are 'quantized' by the ratchet, so you can find an 'optimum' tension point that is between two ratchet points. Which doesn't happen with laces. And for threads (like kevlar thread) it doesn't have the compression strength to be good zip tie. There is a lot of information about what NASA considers to be good and not good wrapping techinques here: http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/401%20General%20Requirements.html http://workmanship.nasa.gov/lib/insp/2%20books/links/section... Also they mention out gassing which is something I completely missed, plastic zip ties have that issue as well. Any void in the zip tie also becomes a real problem in vacuum.
- rhizome 14y agoAs a matter of fact, the article goes into some detail about both why zip ties aren't used and what the lacing might be made of.
- uxp 14y agoSome of the more higher resolution pictures suggest that the lacing is actually made from metal wire or synthetic fiber in a braid, which might have better environmental suitability than an injection molded solid plastic zip tie. Knots also provide endless tightening configurations, where as zip ties have quantified steps, which could simply be over tightened on an essential cable by accident providing a stress point for a small cable or wire to break at in a couple of years. Also arm chair guessing.
- randlet 14y agozip ties are addressed itfa.
- deleted 14y ago[deleted]
- tlb 14y agoZip ties are certainly quicker, but when everything is vibrating they concentrate the cable flexing stress at the edges of the zip tie. I've seen wires crack in my own robots from cable ties.
- ChuckMcM 14y agoWhen there is an 'obvious' answer, its always useful to ask the question "Hmm, zip ties would have been easier/quicker than knots, do they know something I don't?" It is the 'curious' response. If you have used zip ties in adverse conditions you would immediately know they suffer from two huge issues, the first is that under stress the ratchet nib can break and they release, the second is that on a strength to volume and strength to weight ratio they are grossly inferior to any number of threads. So for something you are sending very far away, and for which you have to put 4.3 ounces of launch system together for every ounce you want to land on the surface, mass and volume add up, and you can't really go out and replace a broken one can you?
- stewartbutler 14y agoAlso, zip ties are plastic. Most plastics decay when exposed to ultraviolet. As this is NASA, there is probably some funny polymer that can get the job done, but why fix what isn't broken?
- jasonwatkinspdx 14y agoThree words: read the link.
- noonespecial 14y agoI can't use zip ties on my boat. Two months in the sun and they're toast. They quite literally turn to dust.