The state of the art in copter drones and flight control systems | Hacker News Reader

The state of the art in copter drones and flight control systems

mdpi.com

114 pointsPaulHoule34 comments

We have built drones with open source platform PX4 and NuttX OS for both fixed-wing and multi-rotor drones but each has their own limitations. Fixed-wing is very fuel efficient and travel far distance while multi-rotor drone is the opposite but can perform hovering easily. The hybrid VTOL is basically the combination of the both techniques as provided in Figure 1.

However the taxonomy in Figure 1 is missing a very important class of drone namely gyrocopter or gyroplane. For full size manned gyrocopter it's a beast to control manually but unmanned drone gyroscope will be the way to go due to its energy efficient flight dynamics and it can perform complex manuevering not unlike multi-rotor drones and semi-hovering (can perform loitering but not vertical movements while hovering).

For what it's worth, MDPI has a lot of criticisms from academia as a publisher. Criticisms regarding editorial reliability, methodology acceptance, rigour, etc, etc. Here's just a smattering: https://en.wikipedia.org/wiki/MDPI#Evaluation_and_controvers...

It's been enough where I end up automatically ignoring MDPI papers unless someone I respect recommends one to me. For better or worse. But MDPI made it's own bed in many ways.

Go take a look at Frontiers.

There are reasonable MDPI journals, and reasonable Frontiers. Just like there are predatory IEEE journals and conferences.

You can't just look at the publisher.

A quick shortcut is to look at who are the editors/organizers. If you don't see affiliations from the West, it's unfortunately a very bad sign.

... and plenty of ethical problems in terms of the very business model of Science, Nature, Elsevier and all that. Not to mention what they've done to maintain their comfortable position.

MDPI is the most active RSS feed by far in my collection, they publish a lot of stuff. I'd be interested in getting feeds of Open Access papers on other journals (say from Science) but so far no dice.

I've heard this and actually had a paper published in an MDPI journal. My personal experience was that it was astonishing quick to do so. Usually the submission/review/acceptance/publishing process is many months but this was less than two if I remember correctly. The paper was reviewed and the reviewer comments were reasonable. Not just editorial but with technical comments. So that seemed fine. As soon as we submitted the revised manuscript it was pretty much published immediately. So all the normal steps were followed, just at a faster rate it seemed.

Again, this is my one and only experience with them. I'd be interested if others have any...

those criticisms are from people who think that publishers and reviewers should evaluate scientific papers, when obviously the right way to evaluate papers is by the larger research community over the course of many years. worse, many of the criticisms are from institutions that are attempting to use bibliometrics for hiring and tenure decisions, which is an obviously stupid idea

most papers are worthless, but when they are first written, it is too early to tell which ones they are; of course reviewers' suggestions are often helpful in improving the quality of a paper, but they cannot improve a worthless paper into a groundbreaking one

pre-publication peer review was instituted mostly in the mid-twentieth century and should be regarded as a failed experiment belonging to the age of paper. most peer-reviewed papers are worthless, and peer review often serves merely to retard progress

most of the papers i see on mdpi are mediocre, but some are useful, and it certainly isn't vixra-style garbage

Accusations against MDPI, Frontiers and such take this form

https://en.wikipedia.org/wiki/Predatory_publishing

the claim is that they are ripping off the scientists. Note

https://en.wikipedia.org/wiki/Jeffrey_Beall

was forced to retract his claim that MDPI was predatory.

some do take that form, yes; others are simply complaints that tenure and hiring boards were going to have to evaluate the quality of candidates' research for themselves because mdpi wasn't doing it for them

Peer review is great in theory, but fails because it makes too many assumptions and because the incentive structure. And it certainly doesn't scale well. It's important to remember that the point of publishing is communication. Anything more or less is ill founded.

It is obtuse to think that a few people can read a paper and know it's validity. It's falsifiable but even that's fuzzy. The problem then comes down to the incentive structures. Why do people cheat? Because we're lazy evaluators. It's odd to me that we won't read the works of peers in a department, lab, whatever. But doing that would be a much stronger form of evaluation than anything that could be inferred from citations, h-index, conference ranking, etc. Plus, the structure is to push novelty fast and frequently. That's not only not possible but ignores a fundamental aspect of science: reproducibility.

But this also doesn't mean there aren't scam publishers and publishers scammers prefer. But I'd say that those are a result of the former issue. Because metrics are not being treated as guides. It's just Goodhart's Law in action.

entirely agreed

i don't think mdpi is a scam publisher, but then, i don't read mdpi papers from following some kind of latest-mdpi-papers feed; i read them because other papers cite them, so i couldn't tell you if the utter-bullshit-paper percentage on mdpi is 1% or 99%

i just know i heave a sigh of relief when the paper i'm looking for turns out to be on mdpi, because i know that not only will i be able to read it without hassle, it will have a clearly marked creative-commons license that permits me to archive and redistribute the paper. same with hindawi actually, though i'm mmaybe a bit prejudiced against hindawi papers

Yeah I can't say anything about MDPI, and this isn't in my domain. My domain is in ML and all I can say there is that the signal to noise ratio over conference publications and arxiv papers is within error. But research continues for the same reasons it always has, because people are communicating and niches know their niches. But I think it doesn't bode well for Academia or even industry, who are letting the metrics dictate how they evaluate people. Especially for industry, where things have to end up working. I think Gemini is doing a great job at showing how being great on benchmarks doesn't mean you're a great tool. It's because benchmarks are only guides. When they aren't, they will be hacked (if they already aren't). And that's a dangerous situation to be in.

here are some mdpi papers i have in my bookmarks file; all of these seemed pretty decent, if i recall correctly

http://www.mdpi.com/1996-1073/9/8/622/htm a 2016 #paper on #solar #energy payback times and EROEI (“EROI”) and life-cycle analysis (LCA) and net energy analysis (NEA). In particular fixed ground-mounted “multicrystalline” silicon #photovoltaic cells have EPBT of 0.9 to 2.1 years depending on irradiation (insolation), and an EROEI of 15 to 35. This is surprising because that’s pretty much what it was when NREL published an EPBT analysis around 2001 or so.

https://www.mdpi.com/1996-1073/2/1/1/htm “#Energy Inputs in #Food Crop Production in Developing and Developed Nations,” Pimentel’s #EROEI #paper where he found about four joules returned per joule spent on industrialized #agriculture, #CC-BY, Energies 2009, 2(1), 1-24; https://doi.org/10.3390/en20100001

https://www.mdpi.com/1424-8220/21/2/438 Elfring, Torta, and van de Molengraft’s more comprehensive #particle-filters #tutorial #paper (with #PDF) which supposedly has example code that I can’t find. This is recent (02021) and open-access (#CC BY, I think), and many pages long, and has an overview of a lot of the motivation, but in some sense not very approachable.

https://www.mdpi.com/2075-163X/12/2/220 #CC #paper describes various excavation methods (plasma, foam injection, etc.) including #expanding-grout, which it says works by hydrating lime under confinement and also producing ettringite, but lists four different types: type K (4CaO·3Al₂O₃·SO₃ + 8CaSO₄⋅H₂O + 6Ca(OH)₂ + 74H₂0 → 3(3CaO⋅Al₂O₃⋅3 CaSO₄⋅32H₂O, can be enhanced with silica fume and plasticizer), type M (CaO⋅Al₂O₃ + 3CaSO₄⋅H₂O + 2Ca(OH)₂ + 24H₂O → 3CaO⋅Al₂O₃⋅3CaSO₄⋅32H₂O), type S (3CaO⋅Al₂O₃ + 3CaSO₄⋅H₂O + 26H₂O → 3CaO⋅Al₂O₃⋅3CaSO₄⋅32H₂O), and class [sic] G (CaO + H₂O → Ca(OH)₂). Calls it “SCDA” and mentions ASTM C 845 “Standard Specification for Expansive Hydraulic Cement”. It says they work too slowly (12h) to replace explosives in the usual mining cycle, but I suspect that’s not true of class G, where the main problem is keeping it from reacting to completion before you can pour it into the hole.

Note that the authors are two Latvians and a Ukrainian.

First sentence of today's ISW briefing: "Select Russian military commentators continue to complain about superior Ukrainian drone and electronic warfare (EW) capabilities on the battlefield, continuing to highlight the rapid and constant tactical and technological innovation cycles that are shaping the battlespace in Ukraine."

https://www.understandingwar.org/backgrounder/russian-offens...

Citing blatant propaganda during an active war phase?

Now that's what I call research!

I'm not sure exactly which direction your critique is oriented. The functioning of the Russian milblogger space serves multiple functions, and there are competent ways to learn things from it.

If you're calling the ISW propaganda, shrug.

I think the point stands: if you're interested in the state of the art in drone tech, you're almost certainly paying attention to the Ukrainians and Latvians.

The ISW is so blatantly biased in their coverage they are indeed best though of as an classy looking info-warrior than something like to a neutral observer.

For a long while I only distrusted their political commentary, as it was so obviously shit, at just rolled my eyes when they pretended the Ukrainians didn't send troops on raids toward Belogorod, but otherwise trusted that they at least covered military movements accurately.

Lately I have however seen accusations that they are also uselessly slow at reporting Ukrainian withdrawals, so at this point I wouldn't trust their milblogger coverage to deliver more than selected defeatist posts.

All that said, I think your point that (some of) the state of the art in drone tech is being desperately pushed in Ukraine is a good one. Though I'd add the qualifier that they have very specific concerns and constraints on their drone use (the one-way trips being a prominent one).

> if you're interested in the state of the art in drone tech, you're almost certainly paying attention to the Ukrainians and Latvians

Definitely not to the ISW, though. (Just lmao.)

I wouldn’t cite ISW for anything serious regarding this war. Yes, I am pro-Russia when it comes to this war, but at the same time I respect opinions “from the other side” which are not complete bollocks. ISW is not doing that, unfortunately for them.

Later edit: Just to make sure, I’m not calling bollocks on ISW for this particular statement of theirs (even though I find it highly debatable), but on the information generally coming out of ISW

An omitted use case for the Affordable and Massively Used category of multi-rotor drones: Drone light shows. These are starting to replace fireworks shows as the latter bring up safety and fire hazard concerns.

What a tragedy that would be - nothing replaces the visceral whump of a shell going off. I love it so much!

> nothing replaces the visceral whump of a shell

Expect for having PTSD

drones already / are gonna have this issue too -- funny how these two technologies fill both roles, each in very different ways.

Regarding quadcopters, this video by "Verity Studio" https://www.youtube.com/watch?v=3h1Kh152ygU claims that they have developed a technology to enable drones to continue to fly a little, and then land safely, with just three motors and the fourth disabled.

But to the best of my knowledge this hasn't been implemented anywhere, and today's drones simply fall out of the sky if one motor fails or its propellers are destroyed.

Anyone know why that is? Is the video simply fake? (Comments on the video are disabled, which is not a good sign...)

Even if the video is fake, this seems like an important area of research for drone safety; what's the state of the art?

I remember a paper/ video from ETH Zurich demonstrating this sometime around 2015. There's nothing particularly difficult about it if your motors and controllers are sufficiently overspecced and you're willing to let the aircraft start spinning (you sacrifice yaw control).

Edit: here it is, 2013 not 15. https://ethz.ch/en/news-and-events/eth-news/news/2013/12/new...

> Is the video simply fake?

I don't think so. At least there is nothing impossible about what they are claiming to have achieved.

> Anyone know why that is?

I think the problem is that it wouldn't gain you a new ability. If you are working on something where resilience against failures is important you are much better off with an octo- or hexacopter arrangement.

With that algorithm if a failure occurs suddenly you are in a brand new control regime where the pilot is probably not as proficient. How will they know which way to push the stick when the drone is spinning like crazy? So you probably want a fully autonomous controlled drone (like the ones in the theatre production they are showing).

> today's drones simply fall out of the sky if one motor fails or its propellers are destroyed

There are many systems claiming some level of redundancy. Here is an octocopter setup with some motors intentionally disabled: https://www.youtube.com/watch?v=EeChr2JCfJs

> it wouldn't gain you a new ability (...) suddenly you are in a brand new control regime where the pilot is probably not as proficient

It would be an incredibly powerful marketing message.

The pilot doesn't need to be able to control the drone; the drone would simply land where it is, which, depending on the location, could be not ideal, but in any case much better than falling like a brick...

> But to the best of my knowledge this hasn't been implemented anywhere, and today's drones simply fall out of the sky if one motor fails or its propellers are destroyed.

I'm a former Skydio[1] employee and our motion-planning & state-estimation teams implemented this on all our drones years ago. It wasn't completely fool-proof, but in many non-high-speed scenarios a loss of a motor was not catastrophic and the drone could 'emergency land' within a few meters of where it was flying. I wish I had proof for you but unfortunately no longer have access to any internal videos :)

[1] https://skydio.com

Ref 61 as the single citation for a lot of content in Section 3 claiming that hex and octa copters have more endurance than quads. I'm not sure I agree with that statement and it needs a lot of qualifiers if it is to be relied upon.

As a hypothesis at least it seems probable, just based on lift disk size and proximity. Lift disks closer together form more of an annular lift ring around the craft, for more uniform flow, and larger disk areas in general should lead to increased hovering efficiency.

In my experience flying octa vs quad, the octa definitely outperforms the quad. This was some time ago and DJI has made improvements in leaps and bounds to something like 30mins for a Mavic now? But back then, the octa easily had longer flights as it had larger capacity which was filled by larger batteries. It was also easier to fly/handle. Essentially, I'm just repeating/agreeing with everything they said on pages 11&12.

this has been my experience, too.

more rotors = more power consumption capability, but in practice it yields lower duty cycles for each of the motors. That effect, along with additional lift capacity for batteries, creates a platform that generally stays up longer.

as others mentioned there are also aerodynamic advantages as long as we're staying away from coaxial designs.

Mdpi should fix its format as a third of any given article is whitespace.

Oh, and hi Paul!

Ok, maybe its a quarter.

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