Cable lacing on the Curiosity rover
igkt.net
igkt.net
For example, is it possible that there exists another, more optimal, type of knot that we should have chosen had only our knot theory had been more advanced?
Surely it would be safer to contain those cables in the body? It would just take a rock to fall on the rover from a cliffside or similar to damage those cables.
http://upload.wikimedia.org/wikipedia/commons/4/46/System_Te...
Saturn V instrument unit.
Awesome piece of engineering.
In these kinds of applications, what do they use to attach the cables to something? It looks like on the rover they have special tie points built onto the rover surface -- is that what is done in other applications too?
The first item is amazing as well (ST-124-M3 inertial platform i.e. Gimbal unit for Saturn V)
About: http://en.wikipedia.org/wiki/ST-124-M3_inertial_platform
Pron: https://upload.wikimedia.org/wikipedia/commons/4/44/ST-124_u...
This sort of engineering is as much art as engineering and I truly respect the people who designed and built it.
http://www.amazon.com/Standard-Aircraft-Handbook-Mechanics-T...
Different people like different things. Just because they geek out on something different from what you geek out on does not make them abnormal.
http://www.fieggen.com/shoelace/
I think it is perhaps the single greatest website on the entire internet.
What I find fascinating about this story is I've seen much larger and much more elaborate cable lacing jobs that look just as good at telco central offices and data centers, but its always very vague about what exact part of my NDA or employment agreement I'd be violating by posting (or taking, or distributing) pictures. These mars pictures, cropped, may be the only chance for a civilian non-employee to ever legally see professionally done cable lacing, weird but true. There's a zillion other places to see the surface of mars, but only a few to see cable lacing.
Its interesting that in advertising pictures they always use superglue to make the cables look "PHB-good". So you can't see cable lacing in ads, which is too bad.
Done correctly, cable lacing is, literally, an art form. One guy I worked with "knitted" geometric patterns as he spaced the lacing in various locations and used different colors. Also I saw at least one large example of AT+T being "dot matrixed" into a large bundle of cables by careful spacing of lacing.
Artistic cable lacing is kind of an "apprentice" masterpiece situation, you learn lacing well enough to do art, then you show it to other techs (and your boss) to prove you're not an apprentice anymore, then, sadly, for most techs, no more lacing art work. Oh well.
Another interesting point is that in general, the more specific the sub-reddit, the less it is infected with the type of "reddit culture" that gets so much bad rep here on HN (although occasionally it always gets some, cause Reddit has a shared culture--I personally don't mind, really).
However, this comment, along with the negative comments about the uptime of Tindie's blog (http://news.ycombinator.com/item?id=4472348), has me thinking that these complaints of undue negativity are justified.
I find the attention to detail involved in selecting knots to be a tremendously interesting aspect of sending a physical vehicle to mars, and I find it to be a testament to human specialization and intelligence that there's a whole community of knot experts that can provide so much insight into the knot choices. Implying some sort of OCD around sock drawers seems incredibly rude, and counter-productive to building or maintaining a culture of technical excellence.
However I would say that if you want to maintain a culture of technical excellence, it should be built well enough in the first place to cope with things like occaisional wayward comedy about the possible sock organisiation habits of fans of practical topology, without getting too upset about it.
Otherwise it isn't a very good culture of technical excellence and it will all fall apart the first time somebody sneezes.
[edit] I was also not being backhanded in the first place. You are allowed to include jokes in complements and you do not have to show some sort of undue reverence for people whose work you appreciate when you point out that you like what they do.
The problem with this analysis is that while Dilbert is funny (and fake), you were demeaning (of real people), and your defense uses the same subtly demeaning tone as your original comment.
Also, I would rather you didn't attempt to try and act as some sort of translator for me, as you appear to be a complete and utter dick.
Sorry for my undue negativity about this.
Perhaps there's a cross-cultural interpretation associated with sock drawers that I'm missing. Granted there has been negativity on HN lately, but are we not manufacturing drama here?
//edit: I read it that he's impressed with their focus and passion, which sounds more like a compliment.
I do hope so. As then there is a chance that we might find out what it is and then everything might just make sense. Otherwise I'm just going to paraphrase Keynes and assume that internets can remain irrational a lot longer than I can stay sober.
There's a pretty clear implication that it's silly to "crop out" pictures of mars, focus on knots, and the kind of people that would do that would be OCD in their maintenance of sock drawers.
It's a silly, vaguely cutting generalization. Observe the top reply, which takes a defensive stance: http://news.ycombinator.com/item?id=4474178
Mars itself is neat. But they haven't done much exploration with this rover yet, and so: Knots is what we got. :-)
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.
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.
Less of a concern on Mars, but the edge where the excess is cut away can be really sharp and hazardous as well.
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...
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.
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/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.
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.
Also arm chair guessing.
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?