
Should Quadrotors All Look Like This? - eguizzo
http://spectrum.ieee.org/automaton/robotics/aerial-robots/iros-2013-should-quadrotors-all-look-like-this#.UoRAb7LvVFs.hackernews
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neya
Wow, readers, please do yourselves a favor and watch the linked video in that
article!
[[https://www.youtube.com/watch?v=p8t41avFuCc](https://www.youtube.com/watch?v=p8t41avFuCc)]
though it's slightly WTf-y, it's definitely cool. I'm just wondering - Are
heli's better at carrying my Canon DSLR or would the triquad work better for
this?? Anyone with experience, please suggest, as I am SO gonna build this tri
quad (and integrate it with my Raspberry Pi) :D

~~~
fijter
A heli carrying a DSLR is big, expensive, hard to fly, dangerous and
maintenance intensive. It's good for lifting a DSLR but I would go with a
multicopter, the more blades the better. A hexacopter or even an octocopter
are very stable, easier to fly, possibly cheaper to build and have a fail-
safe, if a motor fails you can land it safely because the other motors take
over. You can find a nice video about the subject here:

[http://flitetest.com/articles/T_Rex_800E_DSLR_Camera_Gimbal](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.

~~~
neya
Thanks! That's pretty informative! :)

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shitlord
Did anyone else watch the linked video of the RC helicopter? It was amazing! I
had no idea that those things were so powerful. The only ones I've ever seen
are the ones at the mall.

~~~
look_lookatme
Link

[http://www.youtube.com/watch?v=p8t41avFuCc](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...

~~~
btown
Is it possible to scale one of those up to Predator-size? Would the limiting
factor be that the power requirements wouldn't scale linearly? Are there
properties of the atmosphere that model-scale aircraft can take advantage of
that larger-scale ones cannot?

~~~
jamesaguilar
Yes. It would be called a helicopter. Full sized ones can have fuel engines,
which can carry more energy per weight and can go further. On the other hand,
they are heavier and not as durable because of that weight. They cannot change
directions like this mid flight.

~~~
aaren
Can you explain why?

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?

~~~
barrkel
Yes.

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.

~~~
mturmon
Right, sometimes called "square-cube law"
([http://en.wikipedia.org/wiki/Square-
cube_law](http://en.wikipedia.org/wiki/Square-cube_law)). Worth knowing about
so you can explain to yourself the differences noted above.

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CraigJPerry
How does this perform cross wind compared to a traditional micro quad?

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.

~~~
loup-vaillant
Accelerometers are bound to detect such adverse effects. Correcting roll and
pitch automatically shouldn't be hard. Also, I would guess that the higher the
main rotor (compared to the centre of mass), the more susceptible the device.
So, if you build the main rotor as close to possible as the centre of mass,
you should have a more neutral design.

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](https://en.wikipedia.org/wiki/Swashplate_%28helicopter%29)

~~~
CraigJPerry
AIUI there's all sorts of considerations & trade-offs. E.g. the motors have a
limit to how quickly they can change output (up to around 400Hz today).

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.

~~~
loup-vaillant
The design I was thinking about puts the lowest rotor below the gravity
centre. First, it would lower the highest rotor, and second, crosswind would
have the _opposite_ effect on the low rotor. I really expect such a design to
be neutral.

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kybernetyk
I always wondered why there are no "real life" sized quadcopters in use for
manned flight. From what I understand the design is simpler and requires less
maintenance compared to "normal" helicopters.

Are there any reasons why we're not flying quadcopters around instead?

~~~
2bluesc
Lady Gaga flies with a hexacopter @
[http://www.dailymail.co.uk/sciencetech/article-2499954/How-L...](http://www.dailymail.co.uk/sciencetech/article-2499954/How-
Lady-Gagas-flying-dress-works.html)

... what the world is coming to?

~~~
pygy_
Morning coffee, this put a big smile on my face.

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?

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jwr
I really like this, because it shows that quadrotor (and flying vessel in
general) research is far from "done".

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.

~~~
Gravityloss
One might almost say that anybody knowing basics of Newtonian mechanics would
say maximizing your blade swept area reduces power needed to stay aloft. Then
there's stuff like tip vortices etc. So just one big rotor is great.

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.

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bambax
It takes (at least) six months to learn to fly a helicopter (or, in the case
of the linked video from the article, probably a lifetime).

It takes ten minutes to learn to fly a quadcopter.

~~~
nakedrobot2
No. Try a cheap quadcopter without any auto stabilization. it takes more than
10 minutes. Maybe 8-12 hours of flying time to become proficient enough to,
say, risk mounting something breakable (like a camera) onto it.

Less time than a normal helicopter though, so I get your point.

~~~
bambax
I have two quadcopters -- that both have auto stabilization: Parrot AR Drone
and DJI Phantom, and it did take around 10 minutes to learn to fly them.

Is it even possible to fly quadcopters without stabilization? Would they not
start spinning out of control as soon as they take off?

~~~
Sae5waip
He probably means "stabilized using gyro _and_ accelerometer" (ie, release
sticks = evens itself out) as opposed to "just stabilized by gyros" (ie,
release sticks, copter stops any rotation but keeps pitched/rolled position).

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?

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speeq
"The researchers explained that the standard "control" quadrotor had an
optimized design, while the triquad was not optimized at all (because its
design was constrained to keep it as similar as possible to the control
quadrotor). This gave the control aircraft an advantage in power of about 9
percent."

I wonder what the optimized "triquad" would have looked like?

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brianbreslin
Is there a video of this thing in action? I didn't see a link in the article
(skimmed it quickly though)

~~~
BrandonMarc
I can't find one, but these links may help:

Dr Paul Pounds, the project leader:

[http://www.itee.uq.edu.au/bme/pounds](http://www.itee.uq.edu.au/bme/pounds)

[http://www.eng.yale.edu/pep5/](http://www.eng.yale.edu/pep5/)

Scott Driessens, his student:

[http://www.youtube.com/user/sdriessens](http://www.youtube.com/user/sdriessens)

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krasin
What software should I use to verify their claims? aerodynamics simulators or
how they are called?

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marvin
This is really cool, and probably a better solution than quadcopters for many
applications. However, what we would _ideally_ want in the end, would be a
tilt-rotor of some sort which incorporates wings. Fixed wings are a lot more
efficient than active lift, and is necessary if you want to squeeze more speed
and range out of your UAV.

~~~
Pxtl
So, like, a remote-controlled Osprey?

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rplst8
I for one welcome our new...

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zobzu
That's kinda stupid garage-scienticism to be honest.

\- 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=qzu5eSZqKpY)
[http://www.youtube.com/watch?v=8QP0QjIsTTM](http://www.youtube.com/watch?v=8QP0QjIsTTM)

So yeah. Not exactly impressed when that's coming from a university. I
expected much better.

~~~
joosters
\- Taking cheap shots about their measures of efficiency is hypocritical. TFA
says that the researchers did investigate the efficiency and calculated a 25%
gain. Presumably their calculations will be in their research paper. You on
the other hand have just given a YouTube video and battery capacities as your
'proof'. Heck, the researchers went as far as constructing a device to test
their efficiency claims.

\- 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.

~~~
zobzu
I investigated and I say this is wrong. No backup either. = The point.

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).

