Should Quadrotors All Look Like This?
spectrum.ieee.org
spectrum.ieee.org
http://flitetest.com/articles/T_Rex_800E_DSLR_Camera_Gimbal
It demo's a Heli carying a DSLR and afterwards (after the first 7 minutes of video) they talk about this compared to multi-rotors. For the best video results you should probably pick the stable octocopter, you can fly FPV as well with a multicopter, great for live previewing your video.
Though quads are much more trendy in the tech world today, as you can see from that video, plain-old RC helicopters are pretty amazing today. The biggest advance in the hobby IMHO has been the development of very small (~1oz) RC helicopters (e.g. [http://www.bladehelis.com/Products/Default.aspx?ProdID=BLH33...) that include the same fundamental control system (called collective-pitch) that enables these large (~10 lbs) helicopters to be so acrobatic. The size shrink brings huge benefits: Small helis basically don't get damaged in most crashes, they mostly can't hurt you, and they are cheap.
Today's super-stabilized and gps-locked quads are like a modern AAA game: you press "A" over and over and watch them go, and say "Wow!". A micro collective-pitch heli is like an old-school game--you're going to need a lot of restarts, but is great fun and will provide many hours/months of challenge.
... and I couldn't help but think, if a life-size helicopter were even capable of such maneuvers, its human occupants would likely die from the G forces.
Clearly such maneuvers seem only possible in an unmanned craft.
http://en.wikipedia.org/wiki/G-force#Human_tolerance_of_g-fo...
I've only seen one live demo of a "pro" RC pilot doing his thing and saying it was awe-inspiring is a massive understatement. These are folks that eat, drink and breath RC and the amount of time and enthusiasm spent is really astonishing. If anyone can find a way around the laws of physics, it's those in the RC community.
http://www.youtube.com/watch?v=p8t41avFuCc
The thought of a weaponized version of that is terrifying. A weaponized and non-human controlled version is straight up Cyberdyne level stuff...
Is it to do with the bulk properties of the materials not varying with scale? Or scaling with some power of length < 3?
If you tried to spec a full sized helicopter engine to make speed changes like those in the video would it tear itself apart?
Mass increases with the cube of scale, while structural material cross-section area increases only with the square of scale. So insects can have miniscule legs, while elephants have tree trunks, proportionally.
Imagine a dozen of these swarming an objective in Afghanistan, expiring their batteries over the course of a 30 minute attack, disappearing, and just when the combatants thought it was safe, another dozen show up because there is a drone acting as a recharging hive for dozens of these things and it's is doing slow circles around the objective.
That's sci-fi sounding and yet seemingly plausible.
We should not hide the uncomfortable truth.
Not that the machines care much about that, though.
'To avoid counting civilian deaths, Obama re-defined "militant" to mean "all military-age males in a strike zone"'
IOW, pretty easy to defend against with a shot gun, netting around your position, and so on. An air strike, on the other hand, not so much.
http://www.nydailynews.com/new-york/queens/teen-killed-remot...
http://nypost.com/2013/09/05/man-decapitated-by-remote-contr...
They're already incredibly dangerous. That trick helicopter just needs one uncontrolled bounce and hit a person and someone will have very very unpleasant day.
Quadricopters seem much easier to make safe afaict.
Overall such helicopters are not insanely dangerous, when operated incorrectly they can be hazardous, but that's also true of ordinary lawn mowers.
edit: One of the above articles explicitly says decapitation. If someone has a coroners report i'm all ears
Let us not sensationalize when we don't know the facts either, shall we?
> “I was playing at the park and we came into the clearing and we just saw a body on the floor,” said Maria Delgado, 13. “He was just decapitated — the whole top of his head was gone,”
People die every day. Being squeamish is no excuse for not reporting accurate and honest information.
> “I was playing at the park and we came into the clearing and we just saw a body on the floor,” said Maria Delgado, 13. “He was just decapitated — the whole top of his head was gone,”
> “I was playing at the park and we came into the clearing and we just saw a body on the floor,” said Maria Delgado, 13. “He was just decapitated — the whole top of his head was gone,”
So I think it's safe to say that a witness report from a 13-year-old who misuses the word "decapitation" doesn't make for a good source.
However, that helicopter seems ideal for antipersonnel rapid assault. Add an ounce of C4 and how could you defend against it?
If you're talking about asymmetric forces, then it's a different ballgame, but I'm still not convinced that there aren't innovative defenses. I saw a game show (of sorts) some time ago where engineers competed to develop a solution to a problem given a very limited set of resources. Some of the ideas the contestants came up with blew my mind.
1: And I still don't think it would be all that hard for someone who is talented with a shotgun.
Its hard for an unalerted human to defend against a fast-moving strike drone flock. Against a civilian - no hope.
So what? It's hard for an unalerted human to defend against a fastpitch baseball to the head too. Because something is deadly doesn't make it practical.
My point is that this is a nonsensical threat (suicide drones) that will not be developed because there are so many effective, and much cheaper methods of neutralizing targets.
I'm not saying weaponized drones aren't a future threat. I'm saying that C4-strapped, wildly-aerobatic weaponized drones are Hollywood threats, not real world threats. The dumb alternatives (bullets, mortars, etc) are too effective and too inexpensive, and the weapons that are high-tech will use more sophisticated attack vectors (like what we're already seeing).
Interested in other attack vectors..what did you mean by that?
How is a drone swarm not human-attended in a way that is distinct from existing drone weapon systems? More specifically, what advantages does a drone swarm have over existing drone weapon systems?
I still think you're missing the reason why this is a non-starter. It's not that they're ineffective (although I'd argue that they are of limited effectiveness), it's that there are too many better alternatives.
> Anybody can afford them; its anonymous; it comes from above so is hard to anticipate.
Russian 50mm mortars are inexpensive and readily available on the arms market. You can drag it through mud, drop it, and shoot it with small arms, and it will still work.
It's anonymous, because the high trajectory allows you to fire from an enclosed position, then simply walk away when you're done; remember they're cheap and available.
When you fire a mortar, it travels a long distance and comes from above, so it's hard to anticipate.
Guerilla forces love mortars. They use them all the time. They get the job done.
The SciFi-fantasty drone swarm is far too cumbersome and expensive for guerrilla forces, and it's too much of a blunt instrument for 1st-world powers.
First-world powers don't need kamikaze drones, because they can field larger, more sophisticated drones that are mounted with more advanced sensors and traditional munitions. They can fire on many targets in succession with terribly effective weaponry like a 20mm cannon. They can fire from altitude where you don't even see them. They can fly in-theater, autonomously until the time that they're needed. They can return to base, be reloaded with cheap ammunition, then return to the theater of operation.
There are some very limited scenarios where the weapon system you're proposing makes sense, but it's a tiny niche. There are too many simpler, effective options to acheive the same result. The only thing this concept has going for it is the cool factor, which doesn't count for much.
Science-fiction? You just watched the video, and you dismiss it somehow as fantasy?
For instance, for assassination, intimidation, even spying (look in a 30th-floor window, relay audio and video) a rotored drone has no equal.
It'll be amusing to see the expression on your face the first time a quad-rotor drone peers in your window. "Hey! That can't be! It's impractical in the scenarios I've imagined!"
> However, that helicopter seems ideal for antipersonnel rapid assault. Add an ounce of C4 and how could you defend against it?
I asked some pretty pointed questions about that hypothetical, and you haven't offered any rebuttal. I've also tried to explore their utility from the viewpoint of a guerrilla soldiers and a nation state.
Yes, I believe that small drones will be utilized. Yes, I believe they will be weaponized. Yes, I believe we really should do something about it! I just don't think the small ones will be weaponized in the way you're suggesting (strap on an ounce of C4 and send them in swarms). That's all.
Actually...
EDIT: Also, according to witnesses, the top of his head was 'gone', so while not decapitated I guess, it was basically the same (if not worse).
At that point (& cost) there are cheaper, more effective (what a cold term) and just down right more terrifying ways, to induce terror.
The small UAVs are destined mainly for aerial photography; they are awesome at that, no question.
spose if you see enough of them it wont look fake no more.
That main rotor will act like an umbrella does in a gust of wind. The micro quads don't suffer the same problem.
I'm not sure of the physics involved (and if anyone knows i'd love to learn more!) but just from hands-on piloting both micro quads and larger helis, the micro quads are some of the least susceptible to cross winds i've ever flown.
While we're at it, I've flown a little toy with two main rotors, rotating in opposite directions, controlling power and yaw, while the tail rotor controlled pitch (the whole thing was auto-stable, so there was no need for roll control). It worked like a charm. So, if we're willing to suffer the complexity of an actual swashplate[1], we could try a design with 2 main rotors, one above, and one below, hereby getting a neutral, manoeuvrable, and (hopefully) efficient design.
[1]: https://en.wikipedia.org/wiki/Swashplate_%28helicopter%29
Because there's no swashplate on the upper rotor of those wee co-axial rotor designs, they're really ineffective in cross wind. You can't apply the required corrective input when the top rotor gets blown off axis.
That said, in this design, having two different types of rotors mounted non-symmetrically seems bound to induce some yaw from winds.
Are there any reasons why we're not flying quadcopters around instead?
> First, quadcopters do not require mechanical linkages to vary the rotor blade pitch angle as they spin. This simplifies the design and maintenance of the vehicle.
As already mentioned I'm blatantly ignorant about this topic so it would be nice if someone who knows this stuff could chime in :)
small quadcopters basically speed up and slow down the motor itself to control how much lift is generated. As the size and weight of the blade increase, inertia makes that impractical, so you have to go to variable pitch for control.
... what the world is coming to?
She (or, probably, her team) has been hacking the entertainment scene for a while.
Dubbing "a dress" what would otherwise be considered a nerd toy is genius. What's not a dress for her?
The explanation is simple: quadrotor physics do not scale up. The rotational inertia of the rotors is proportional to the length of the rotor blade to the fifth power. Double the rotor blade length and the inertia of that rotor goes up by a factor of 32.
High inertia rotors are not suitable for quadrocopter because fast changes in the rotation of the rotors required for maneuvering them.
Having one big rotor for lift and three (or more) small ones for control is a very good idea. Another idea that is being researched is having multiple quadrotor copters flying in co-operation.
Assuming mass scales with length, inertia should be proportional to the third power. Where am I wrong?
Unfortunately I can't remember the source where I saw the 5th power figure.
In addition, the aerodynamics of a rotor don't scale up linearly either.
The name "Discojet" is way more badass name than "Skycar." Just another sign of lowered expectations.
I wonder how much damage he does to the nascent industry if personal flying vehicles by sucking all the oxygen out of the room.
Most people would tell you that you'd be insane to try to design new types of aircraft, because we already know how to do that. This research proves otherwise.
The problem becomes control. With many small rotors you don't need to control blade pitch, as the electric motors have high torque and the blades are light, so you can control with quick engine thrust changes. And it's that what makes the quad rotor system much more attractive than a normal helo. The traditional helicopter pitch control system is complex and requires precise high stress components that are well built and maintained.
But it's a very inelegant brute force system in my opinion. The pitch control could be improved a lot as well if you have powerful electromagnetics with very precise control.
You still need a tail rotor though.
The real helicopter is seeing some real progress at the moment as well, all in the name of higher speeds. There's Sikorsky's X2 and AVX's modified Kiowa. They have coaxial main rotors with a pushing tail rotor and two pushing fans respectively. Then there's tilt rotors by Bell and Boeing, IIRC. These were, at least at some point, all part of a US scout helicopter competition. And then there's the Eurocopter X3, with no tail rotor but twin pulling rotors like a twin prop airplane. X2 and X3 have flown.
It takes ten minutes to learn to fly a quadcopter.
Less time than a normal helicopter though, so I get your point.
Is it even possible to fly quadcopters without stabilization? Would they not start spinning out of control as soon as they take off?
Sure, learning to hover in one general spot is doable in 10 minutes. I wouldn't call that "learning to fly".
What about very basic maneuvers like landings (no bouncing around, no dropping from too high, and at the spot where you wanted to land) or circles/eights, dealing with ambiguous orientations when your copter is high enough (~ 6m ?), nose-in flying / dealing with control reversal and recovering from orientation loss?
I wonder what the optimized "triquad" would have looked like?
Dr Paul Pounds, the project leader:
http://www.itee.uq.edu.au/bme/pounds
Scott Driessens, his student:
- TFA does not mention the stability issue. Guess why people and drones fly tri, quads, etc and not regular helis. Yeah. (a simplification: stand on one leg. Now stand on 2, and use your 2 hands as well. 4 legs. Stable heh?)
- Yes single large prop is more efficient than many tiny props. But put many large props and the difference isn't so big. Let's take a $1000 ultra efficient quad: www.youtube.com/watch?v=t0SR5bzuFq4 yeah thats 100min of flight time for something smaller than the Align Trex of the video. And it's cheaper too.. The trex flies 5 to 10minutes (6S 5000mah). At equivalent batteries, the trex flies 25min (hint: the trex is not made for efficiency, it's made for 3D). An average camera-less quad flies 10 to 15min (3S 3000mah).
- TFA compares a $5000 Align Trex 700 with a bunch of expensive upgrades - the top of the top - with one very good pilot with decades of training... to a $200 toy.
- $200 toys made of wood and plastic flown by random people are actually pretty good at acro. Why? Because being more stable they're much easier to fly. Ex: http://www.youtube.com/watch?v=qzu5eSZqKpY http://www.youtube.com/watch?v=8QP0QjIsTTM
So yeah. Not exactly impressed when that's coming from a university. I expected much better.
Maybe there is something more complicated going on with helicopters that I am not aware of, but a helicopter would not be an inherently stable system due to it "hanging" from the rotor because the direction the rotors are providing thrust changes (all other things being equal), when the helicopter starts to tip one direction.
- The stability might be an issue for completely manual flight (but then, people fly ordinary helicopters just fine...) but with computer-assisted balancing, the problem can be much reduced. Even existing quad copters often have computer-aided stability.
Now then again, I actually fly every of these so I pretty much know what the efficiency is.
YES they gain 25% efficiency with the tricopter that has a huge prop in the middle, I TRUST that. But the test is meaningless:
If you change the 3 props instead and put big props, with corresponding motors. Guess what. Efficiency is probably higher than the 25% difference. I actually design my own. In fact, I also design my own control boards (the software that is)
Quadcopters use accelerometers, barometers, gyroscopes and magnetometers (and GPS) to ensure stability. Guess what. Measurement from these devices isn't 0ms. Actuating the motor control isn't 0ms.
On regular 1 rotor head heli it isn't either. In fact, it's longer.
Result? it's more stable with 4 props than one prop. It has more inherent stability., even if it wasn't "computer assisted". Timecop did a fully gyro stabilized quad copter recently that shows exactly that, if any "actual proof" was needed. Gyro stabilized can be made with no computer whatsoever (like helicopters are/used to be - that's why they're very, very hard to pilot, real ones and RC ones).
The sikorski prize was claimed a few months ago.
http://www.youtube.com/watch?v=syJq10EQkog
you can get a 600 or 700 class that can do "3D" flying as in the video for much less than 5k. The entry point is below $1k.
their configuration makes sense to get the best features of both. it's not solving all problems but it's an improvement over quads for some tasks.