What to Do After Finding Hot Connectors on Overhead Power Lines (2017) [video]
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I don't know the first thing about helicopters, but the negative feedback circuits that keep things steady in many applications, from power supply voltages to Segways, could help with that.
It's a very simple basic concept that has been around for many decades, even before analog electronics, never mind digital devices: https://en.wikipedia.org/wiki/Negative_feedback
(I repeat I do not know if they are available in helicopters. It may well be the pilot doing it by hand the hard way.)
https://en.wikipedia.org/wiki/AgustaWestland_AW139#Design
https://en.wikipedia.org/wiki/Eurocopter_HH-65_Dolphin#Desig...
Check out: https://github.com/betaflight/betaflight/wiki
Granted, it's for hobby scale drones, but the same principles apply.
https://github.com/iNavFlight/inav/wiki
The underlying differences in how they fly aren't that relevant. You have a six-axis IMU, various controls that influence how the craft behaves in those axes and various PID loops that influence the controls.
I don't really understand the downvotes. Obviously, having a type certificated auto-pilot for a commercial helicopter is a world apart from the flight control system for a hobby-scale drone, but the gap between them has nothing to do with the technology and everything to do with the process of type certification.
My point is that it's pretty impressive what these software projects are able to achieve with sub $100 MCUs. Some of them now have 32khz control loops with 32khz IMU sampling. Anyone that's ever peeked under the hood of a commercial auto-pilot would be amazed by that.
You can read Maxwell's On Governors from 1868 and see that, although it explores their math in some detail, it doesn't attempt to generalize beyond braking or otherwise slowing down steam-engines: https://www.maths.ed.ac.uk/~v1ranick/papers/maxwell1.pdf
So, although devices with negative feedback had been built for centuries — and many natural or simple artificial objects can be usefully analyzed in terms of feedback — the general idea of negative feedback as such seems to date from the 1920s, and apparently Black discovered its usefulness in 1927. The idea was so outlandish at the time that his patent was initially rejected as describing a useless invention — why would you want to reduce the gain of an amplifier? It wasn't public until 1933.
After Black's invention, which upgraded FDM for long-distance telephony (the "carrier system") from three voice channels per wire up to nine, then dramatically more, and permitting long-distance circuits with a sequence of 34 repeaters, rather than, say, three.
Bennett's "A history of control engineering, 1930–1955" discusses this history in detail; find it at your favorite library.
At the same time, in 1922, Minorsky formalized PID control, which gets into negative feedback from a different angle, that of automatic ship steering.
Black's, Minorsky's, and earlier negative-feedback designs were not generalized into a general theory of negative feedback until the work of Nyquist and others in the 1930s — most prominently, Wiener!
Nowadays, explicitly designed negative feedback is far more ubiquitous than your comment suggests. By far the most common analog circuit component, for example, is an op-amp, which is almost invariably applied with negative feedback; also, though, negative feedback is central to nearly any kind of homeostasis, optimization, or stable static mechanical equilibrium. So, for example, we have negative feedback in TCP bandwidth usage, in glucemia, and in your toilet tank. Parkinsonian tremors — the opposite of your "very steady hand" — are now being analyzed as oscillations in a negative feedback system involved in human motor control, though the theory is not yet fully mainstream in neuroscience.
As for "digital devices", those date back at least to Leibniz; they are far older than analog electronics, which in turn are a couple of decades older than the concept of negative feedback.
But I get the feeling that a large part of the audience here is not that aware of those possibilities - I was just pointing in that general direction.
I mean, sure, the general concept of feedback is "simple" and applicable to helicopters, in the same way that addition is "simple" and applicable to planetary orbital dynamics.
But even basic control theory – what you'd need to actually stabilize a dynamic system as complex as a helicopter – fills a textbook or two, and the field is still evolving. [1]
Not to mention that the whole concept of "hovering" is damn difficult for a machine to quantify. You'd need LIDAR and/or visual tracking systems to accurately hold your place in all six dimensions well enough to keep a worker next to a powerline, and only in the past decade have those even become good enough for use in land-based vehicles.
I am not that good at math, but I feel like if I was trying to solve that problem, it should be as simple as finding someone smart and saying "use a Kalman filter"...
In one sense I can't say it's "simple" or "basic" because I can't do it, but I'm under the impression that it is a manageable solved problem that can be summarized in four words. Is that wrong?
There are – like I said – entire textbooks on the subject – and why it is complex – if you are genuinely interested. I mean, heck, there's two textbooks alone about one particular system I randomly found on Wikipedia [1].
However to directly address your misconception, Kalman filters are not control systems. They are related to control theory, and are used to provide inputs to control systems. But control theory is its own thing, and there is no "general" solution to correctly control any given system.
In a lot of fields, elegant analysis has given way to cheap brute-force application of computers that is easier to generalize - that's what I'm fumbling at here.
After all, if you or I try to balance a pencil on our fingertip, we are not doing the math on that wikipedia page in our heads. We are in fact using something more akin to the brute force method - sense, synthesize, act, repeat.
Piloting a helicopter in general requires an incredibly steady hand on unintuitive controls that interact with each other in ways that are difficult to predict[1]. Being able to do that with high precision, a disturbingly small margin of error, and fatal consequences for almost any error is basically a superpower.
[1] SmarterEveryDay has an interesting video[2] about learning to hover a helicopter, which apparently requires trying to hover (badly) until the brain learns how to abstract away all of the complexity.
The best analogy I've heard: imagine trying to stand on a basketball. Now imagine trying to stand on a basketball without flailing your arms around. Now imagine trying to do that for half an hour while someone's life depends on you not screwing up even for a single second.
More to the point, helicopters and power lines have both been around a lot longer than helicopter autohover technology, and aviation is an inherently conservative enterprise. Even if these sorts of repairs are being done using autohover today (I don't know) they were surely flown manually in the past.
UPDATE: I asked this question on /r/flying and got this response from an actual helicopter pilot:
https://www.reddit.com/r/flying/comments/998c8b/helicopter_p...
"In a low energy state like an OGE hover, and especially when doing dangerous work like utility (as in the video), live hoists, etc we are almost always handflying. You would be surprised at how few helicopters out there are even capable of auto-hovering. We have an IAHAAS system on the Pave Hawk which in theory can do things like auto hover, auto land, maintain radalt and baro altitudes, even fly zero vis approaches etc. but we don't trust it. I have personally seen it do some sketchy things like virtually departing us from controlled flight during a steady hover for literally no reason."
Cars with automatic transmission don't have a "backup manual transmission" for when the automatic transmission fails. The automatic transmission doesn't fail.
Um, what kind of car do you drive?
And all those transmission repair shops are doing... what, exactly?
Actually, that is exactly what we're talking about. Why would you doubt it? You not only need to keep the helicopter oriented, you need to keep it in the same place, i.e. you need it to follow a zero-velocity trajectory. Why would you think that this is any different from a regular autopilot?
The kind of system I'm talking about here, on the other hand, is essentially a physical model of the three available controls and how they interact to move the aircraft (and thus predict how the aircraft will be moved); combined with actuator-sensors, accelerometers, and gyroscopes to read off how the aircraft is being affected by those controls (and thus correct the prediction)—enabling you to translate linear movement of a flight-stick to linear movement of the helicopter. It's a dynamic torque model feeding a control system, with a user-supplied reference point. You can make an ASIC that does that and put it through fuzz-testing for literally every potential input combination it'll ever receive.
Yes, said ASIC might physically fail (even after you've done an extensive burn-in test)—but, given the tolerances we have in making ruggedized solid-state electronics these days, vs. the tolerances we have in making mechanical systems, it'd be the least likely part in the control chain to fail.
It is true that state-of-the-art navigation systems operate the way you described. But airplanes have been flying for over 100 years, and there have been autopilots for nearly all of them (the earliest autopilot dates back to 1912). The vast majority of airplanes flying today do not have state-of-the-art systems.
Helicopters can also have advanced and full integrated routing systems that will complete an entire trip from A to B, just as fixed-wings can have a simplistic input-to-output linked autopilot that just aims to keep the plane level and with the same heading.
So yes, an advanced system is more complicated than a simple system, but both systems can fail. And since that is inevitable, it's usually better to have a complex system with redundancy that will tolerate failure, than a simple system with no backup that will lead to catastrophe.
Automatic transmissions fail all the time, and then the car stops moving. Ok for cars but serious problem for flight so these aircraft have multiple automatic and manual redundancies.
Helicopter autopilots are indeed full guidance systems like fixed wing aircraft, but they can hold the craft in hover position because it's just another flying position possible for helicopters, but it is still actively flying.
Other parts of the automatic transmission system fail, sure, but those parts are the same parts that are in a manual transmission. (Because, after all, in modern cars, a manual transmission's control system still ends up as signals sent to an electronic gearbox.)
So, like I said—in modern cars, where you've just got an electronic gearbox anyway, there's no sense in having both the ASIC issuing control-commands to the electronic gearbox, and a backup manual stick for issuing the same commands. If there's any fault in the system, it's far, far more likely to come from the stick's mechanism breaking down and issuing spurious commands, than from the ASIC breaking down and issuing spurious commands. And more likely than either is the gearbox getting messed up because it's sitting in a hot, dirty engine compartment.
In 2018, it is possible to have a car with an ECU that is 30 years old, and I happen to have one. Solder joints can go bad over time, and repairing the control unit is a thing that people do on cars like mine. If I was looking forwards regarding some other bit of electronics, I would probably worry about capacitors too.
That has more to do with aggregate risk management predominantly driven by predicted MTBF, failure mode analysis, and safety criticality levels.
Either way, failure is not unique and can happen in either domain. There are plenty of examples of electronics failing and again it is strange to say that they don't. Silicon chips might not move but they are physical products that can overheat or short-circuit or just break.
Aircraft are much more critical than cars and the reason they have multiple completely redundant systems is precisely because things do fail all the time.
To be sure, it's not because they fail all the time, but to probabilistically address the risk that if Murphy does come knocking, consequences won't be immediately catastrophic.
I only meant to clarify that aircraft redundant systems exist because failure mode consequences would be catastrophic with unacceptably high probability otherwise; not simply because things in general fail all the time, as was asserted.
It's a subtle yet significant difference that other readers in passing may not recognize.
No, they don’t (so long as you are talking about stick-shift and not paddle shift).
Autopilot systems, however, are only as good as the people who program them. A helicopter, as mentioned elsewhere, is dynamically unstable and requires so many tiny inputs to maintain steady flight, let alone hovering. Just like in Teslas that 'nope' out of their Autopilot systems back to the driver milliseconds before a crash, a pilot has precious little time to retake control should the electronics fail.
Car ECU keeping your car moving in one dimension (forwards) - fairly safe to let a computer take over, minimal danger if it fails.
Autonomous technology keeping your car moving in two dimensions (forwards AND steering) - very complex, very little time to retake control in a failure scenario, very dangerous.
Autopilot keeping your helicopter moving in three dimensions - I think you get the idea by now :)
Until the technology is good enough for taking the pilot away, it's not a gain.
If that were true modern airlines wouldn't have autopilot.
And by the way, there's an ongoing discussion on airplane groups about all the new failure modes created by the autopilot-pilot interface. It creates plenty of problems.
Regarding drones, I suspect that you are at least partly right. There is a lot of interest already in drones as inspection platforms. Perhaps they will go farther as drones get more commercial aviation clearance.
I'd imagine the reason a DJI drone's capabilities are so much greater than those of a helicopter carrying passengers is that the former can fall out of the sky every now and then and it's no big deal. The latter has to pass a whole lot of rigorous FAA (or equivalent) testing.
This reminded me of another comment I read recently, and I was actually able to remember where I read it! https://news.ycombinator.com/item?id=17723107
> Hi- I used to work in regulated pharma and I want to be clear: " The core problem is that the FDA-approved devices are optimized not for getting the best result, but for ensuring the manufacturer can't be blamed if something goes wrong" is a misleading statement. The reason everything is regulated is that sometimes things do go wrong, and it's necessary to have root cause attribution so the problem can be remedied and a fix deployed, and, if somebody did something illegal or dumb, they can be sanctioned.
(The quoted part of this comment, itself from a previous comment, is the part I found relevant, but I quoted the whole thing (reply and all) because I found the whole thing interesting.)
I think I can naively say with confidence that aviation and medical certification are very similarly rigorous.
So, it sounds to me that the autohover functionality you describe was perhaps the equivalent of Tesla "Autopilot" (which really amounts to auto-steer). The context of doing rescue lifesaving over sea is indeed very stringent, but at the same time, it's not going to be the end of the world if the helicopter moves around a bit, because it's in the open air. And if the situation is dire - strong crosswinds, or someone in critical condition - the pilot's training probably instructs them not to use it.
In this situation, letting the controls go for 2-3 seconds (as per the other comments here) is going to mean an unrecoverable crash, and perhaps a rotor blade might cut one of the cables and then you have 220kV waving everywhere, hitting other power lines, touching the ground..... no. You just find the best pilots that can hover Really Well™, and pay them metric stupid amounts of money so they don't go anywhere else.
Now I'm wondering if the pilots hold hovering competitions, in the same way people in the military frequently do target practice.
Yes. Have a read of "Rescue Pilot" by Jerry Grayson. It's a great read. He describes how they used to practise hovering with a single front wheel resting on the top of a particular coastal rock formation. It was a competition in the sense that one crew upped the ante by managing to balance their tail wheel on the rock, so the rest of the crews followed.
[1] https://www.bloomsbury.com/au/rescue-pilot-9781472918840/
Edit: Another link: http://rescuepilot.net/
Yet another book to add to the wishlist... I'm gonna need a job that gives me a bit of spare time, the pile is getting pretty big, haha.
The Vulcan bit leapt out at me; I've also read Vulcan 607! That book was purely technical; I would have appreciated an explanation about the political upheaval going on with the RAF at the time as well, I had absolutely no idea.
I had no idea hovering over sea is as complex as it is - of course everything underneath the helicopter is going up and down. So the helicopter needs to match that if it doesn't want to whomp onto the deck as it lands. Hah.
And so, in the same vein, hovering over a ship doing rescue operations is clearly going to preclude the use of the kind of autopilot described in the GGP comment.
I've been interested in the idea of flying since I was about 15, but I've been dragging my feet on getting involved for years (I'm 27 now) - if I love it, I'll be depressed I can't afford to dive right in, but if I hate it or can't get my head around the flight controls (I have poor hand-eye coordination, a lot of visual things don't "click" for me, and I can't keep an RC helicopter in the air), I'm not sure if I'd handle the let-down. Because of the expense involved I'm a bit on the fence about it.
Various health issues are why I didn't go the RAAF route a long time ago. (I'm not even sure what to name my condition - I've briefly described it at https://news.ycombinator.com/item?id=15005811 and https://news.ycombinator.com/item?id=17780498.)
At the end of the day, any mistake at 5 foot or 50 foot away is likely to be fatal!
I havent seen a quad that can autorotate, a necessary emergency trick if you want to carry people. When the power fails on a quad it just falls. Traditional helos can actually glide to a controlled landing.
Autorotation is where helicopters get their speed/altitude restrictions when carrying passengers. They generally are not allowed to hover at low altitude because from there they cannot safely autorotate onto the ground. If drones want to carry people, or carry heavy things over people, then they will need to develop some sort of plan. Total engine failure should never result in the total loss of the aircraft.
Admittedly it would be a pretty terrifying ride to the ground, but preferable to plummeting. There’s a lot of rotational energy in the aircraft though.
I think there’s probably significant scope for improvement in redundancy of these systems.
However, it may be that using some other form of control than a mouse works better.
[1] namely, Thrustmaster T-Flight HOTAS X, IIRC
Plus you're very highly-motivated to stay alive.
When all helicopters are quad, tailless, designs flying will be much easier.
If it required similar skills to a human standing on a basketball, then a Helicopter is an monumental engineering failure.
That's baffling. Engineering is the art of compromise. The helicopter _does_ have many compromises in it's design, but it's benefits are unmatched by other aerial vehicles. In other words, the benefits outweigh the negatives.
I’m not really into aviation and don’t have any helicopter pilot friend.
https://www.reddit.com/r/flying/comments/3zzajl/fire_pilots/
They sent out flyers to all the residents a few days ahead. This video shows once splice. I can't imagine the crew (or crews) that were working the miles of lines behind our house doing this for multiple days in a row.
The arc when the helicopter finally disconnects from the power line is pretty astounding. To the lineman, it's all in a day's work, I guess.
At those kinds of temperatures, oxidation is much faster, and you'll get heating and cooling stresses causing micro fractures as the load on the line goes up and down.
As the resistance increases even a little, the temperature will increase more, making the above effects even worse.
They probably just make sure the wind isn't gusting too much.
Nevertheless, it's the same for the weather, Fall/Winter is gonna be windy enough you can't wait around for it.
All in all, I wouldn't extrapolate too much from that little statement.
Also there will be more wind at 200 feet than at ground level
Not an issue when any electrical ground is at a far distance.
I don't understand why there's an arc at the end when the lineman disconnects and pulls away the safety rod. That's there to keep the helicopter at the same potential as the transmission line, right? So why's there a potential difference when the safety rod is withdrawn?
Assuming a spherical helicopter 1M in radius, the capacitance to ground is
>>> 4 * pi * 8.8e-12
1.1058406140636071e-10
>>> 60 * 2 * pi * 220e3 * 1.1058406140636071e-10
0.009171625977844317
>>> 220e3 * 0.009171625977844317
2017.7577151257497
(and all of this of course assumes that the metal helicopter has low enough resistance to charge up to the full voltage)
I think 220 kV is the RMS voltage, so you get RMS current from the formula above. Peak voltage would be √2 * 220 kV.
Indeed, both the capacitor and the arc are in series, so actual current and power is somewhat less. As the arc grows longer, there should be an optimum length where you get 1/√2 of the maximum power.
Apparently there are other factors as well. This StackExchange answer can address it better than I can:
https://aviation.stackexchange.com/questions/9357/can-rotorc...
I have no source for this, just amateur reasoning.
AC makes isolating rather complicated since increasing your resistance to ground naturally turns you into a capacitor which acts like a resistor in AC (which is why thin rubber soles on your shoes don't protect you, you want think ones to increase resistance and decrease capacitance) so a small current will flow.
At high voltage this small current can still be transmitted over an plasmaarc.
How did the lineworker and helicopter not get electrocuted? Is it because they attached themselves to the transmission line, similar to how a squirrel doesn't get electrocuted? Or were the lines taken down or something (I find that hard to believe but maybe). At those levels, if they were at the same voltage as the lines, isn't there still a risk of arcing to another line?
Edit: Misreading on my part. Parent meant "a line closer to the tower" not "a conductor within the line."
When the work is done, the above is reversed to extract the worker.
There's a segment showing this in "Modern Marvels" episode S11E45, "Wiring America" starting at 23:44 [1].
I've also seen a documentary somewhere [2] that was similar but more focused specifically on line work. That had a clip showing a worker being lowered to a particularly difficult to reach conductor. There were at least 3 horizontal layers of conductors, with at least 3 parallel conductors in each layers, and the one needing work was in the middle horizontally and had at last 2 layers above it.
For that one, they had several dry wooden poles connected end to end to form a kind of chain. They put this together in a dry area, then had a crew carry the pole chain outside careful to not let it touch the ground, so it would not get wet from the morning dew on the ground. One end was attached to the helicopter, which slowly started lifting it, with the crew that was holding it making sure to not release segments until they were sure they would not swing into the ground on the way up. Finally, the line worker was attached to the last segment. From then on, it was similar to the segment from Modern Marvels.
They used the dry wooden pole chain because there was no way to reach the work conductor without whatever was suspending the worker simultaneously touch two of the above conductors, so it was imperative that this not short out things.
I believe they used a pole chain rather than some non-conducting rope because a rope can get tangled in things or wrap around things. The pole chain consists of rigid segments, which are not going to get wrapped around anything.
[1] https://youtu.be/vuRNs50VMJ0?t=23m44s
[2] Probably on the History Channel or Discovery Channel.
It doesn’t look like the safest job in the world, but a lot of crazy-looking things can be reduced to tolerable levels of risk with lots of training and good, methodical procedures.
After all, packing a couple hundred people into a pressurized tube six miles above the ground is pretty crazy too, and used to be fairly dangerous, but these days it’s the safest way to get from A to B.
I have no idea if they work as well as advertised though, hence the question.
I've seen those things crawling along a nearby power line a couple times, although these particular ones seemed too small to be able to do anything besides inspecting the line with a camera/sensors. I'm not in the US though, things are different here, we don't use aerial transport on every occasion.
EDIT: on a further inspection, the robots seem to have issues with crawling over more complex line sections, and are used mainly on very high voltage lines. Apparently, the tech is still in its infancy.
Not sure what they do if the line to be fixed is not the one on the top (fixing one of the lower lines would mean the helicopter interferes with the upper lines).
There is no way to ground (other than capacitance which likely causes the arcs you see in the video)
According to a comment elsehwere based on capacitance the amount of current flowing is rather low and not immediately dangerous.
OTOH, the only thing I've ever seen take down high tension towers was an ice storm so bad, they collapsed under the weight.
https://www.google.com/search?tbm=isch&q=2016+South+Australi...
ahem, I never said that only ice was required. But those towers didn't just fall over on a calm summer's day. :-)
It did cost over $2B to rebuild the network.
https://www.cbc.ca/news/canada/montreal/ice-storm-1998-1.446...
Above ground is the way to go since it's cheaper to construct and much easier to service when things go wrong.
For example, if you'd simply stick a high voltage line into the ground, then there would be a voltage gradient between the ground voltage far away and (almost) the line voltage directly at the place where you stuck it; and since the earth isn't a very good conductor (compared to e.g. yourself), if you walk towards it, then the "step voltage" between your leg closest to the wire and the other leg can be sufficient to kill you.
That being unavoidable (vehicle on fire, etc.), don't walk away from the vehicle, jump, two feet at a time, and keep jumping that way, until you're a good distance away. This avoids you ending in a situation where you have that step voltage between the voltage rings.
Here's the tl;dr version: https://hackaday.com/2015/07/27/find-and-repair-a-230kv-800a...
More importantly I want to understand how to let go of such inhibitions (and thoughts) of not pursuing such ideas..
Overhead powerlines developed gradually from an overhead line running power from one side of someone's lab to the other, to power running between buildings, to city wide distribution and beyond. As time went on, the powerlines got larger and higher voltage.
There aren't a lot of options -- underground powerlines are possible, but they have their own disadvantages so are not a clear-cut winner.
The damaged section will have a higher electrical resistance than what it was designed for, and as a result that section will dissipate more energy (heat). The splice/patch effectively increases the cross sectional area, which will lower the resistance, which will lower the dissipated energy, which will lower the heat.
https://www.youtube.com/watch?v=oBJyyEAw-6g
I sincerely hope it's the actual lineman talking and that he takes a job in voice work when he retires.
You probably get good benefits and disability securities, and overtime pay. But it means working in dangerous, frequently laborious, conditions, working away from home all over the province/country, and working frequent overtime. Makes me scratch my head when the people holding the infrastructure together get compensated so little.
Because they are very far away from where value is captured. That's a seriously annoying part of the way capitalism as we know it works: you only get paid a substantial fraction of the value created if you are near the point of value capture. That's why sales people tend to earn well.
Although looking closer, it looks like it's the flexistrap type mount put over a smooth helmet, so makes sense.
Point is, kludges are everywhere!
B) you can also see someone holding the other camera on the ground, as well, which is interesting to see.
If you're referring to the helicopter,I believe they already have helicopter mounted saw blades for trimming trees, in particular, for transmission line corridors.
See here: https://youtu.be/Pla06PO6Odk
The first thing they do is attach the platform to the cable. They use the "wand thing" first, so that their hands are away from the inevitable sparks, and allow the platform he's sitting on to equalise (voltage wise) with the wire. In other words, he's sitting on a platform thats 10k or more volts! Once equalised, a hook is attached - this is also conductive.
Once the job is done, the wand thing comes back out - the hook is detached, without sparks as their is an alternative path for the electricity through the wand, and then the wand is slowly removed.
Linemen are nuts!
Same like you should do on your car wheel. First put them all ass much as you can without force, then apply force. In a star bolt pattern.