
Throwing and catching an inverted pendulum with quadrocopters - eguizzo
http://robohub.org/video-throwing-and-catching-an-inverted-pendulum-with-quadrocopters/
======
jawns
I keep trying to think of practical implications for this technology, but
every time I do, I just end up daydreaming about robot circuses.

~~~
devindotcom
Something that popped into my head is a drone tossing a grenade through a
window. The military would go nuts over this.

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sliverstorm
What happens when somebody else develops a drone to catch & return grenades
thrown in through your window?

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sliverstorm
(I'm guessing the answer cumulates in anti-drone drones, e.g. air superiority
drones. Drone dogfights!)

~~~
elektronaut
Or simply stronger windows.

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slurgfest
Or a person can use a grenade launcher

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zacharydanger
I couldn't figure out _how_ the quadrocopters were coordinated. Turns out it's
a high-speed motion capture. More here: <http://www.flyingmachinearena.org/>

~~~
beambot
I've ranted on this topic before [1]. I still think it's a bit dishonest...
academics shouldn't promote their work to general audiences without properly
denoting caveats. In this case... they're using a ~$50k vicon motion capture
system that returns millimeter-precision pose estimates at ~1kHz.

[1] [http://www.hizook.com/blog/2012/07/02/being-honest-robot-
vid...](http://www.hizook.com/blog/2012/07/02/being-honest-robot-videos-
motion-capture-speedup-rates-and-teleoperation)

Without the vicon and (probably) a central control PC, this feat would be
SUPER difficult -- by ~1-2 orders of magnitude. The real problem is: when
someone does solve _that_ herculean problem, the general public won't care.
They'll just say, "eh, we've seen that before."

~~~
snowwrestler
Who cares what the public thinks? The funding and eventual commercialization
will come from people who do understand what is going on here.

I'm no expert, but I would imagine that research using remote viewing and
centralized processing is just a first step that could make it easier to
validate particular solutions, which can then be "baked into" self-contained
platforms.

~~~
beambot
It's the same as industry... good PR goes a long way toward acquiring funding.
Would you be upset if (say) Apple, Google, or Microsoft's PR machine was
intentionally deceiving folks? Academics are even more sensitive to this --
it's why we're always railing against "shitty science reporting."

Also, I suggest reading the article. I _am an expert_... I greatly admire this
group's research(!!), which is why I don't mind giving 'em some tough love.
But I also want the group that "cracks the egg" for self-localization and
decentralized control to get their deserved limelight. This video makes that
less likely.... as evidenced by the fact that so few people in this thread
(probably) know what a Vicon is, how it works, or that it's being used.

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ChuckMcM
That is insanely cool. Quit your job and play with quadrocopters cool.

I'm surprised we've not seen larger versions of this platform for civilian
use.

~~~
Ao7bei3s
They have been in civilian (private/commercial) use for a few years (since
2008 or so). Mostly for taking pictures from above -- they are relatively
well-suited for that. (And for fun flying of course)

For transporting big things: it's more efficient to have larger rotors than to
have multiple rotors.

For transporting really big things: see above, and helicopters have been
around for a long long time; "we" (not me) have decades of experience with
helicopters; you probably _really_ want something that is safe and reliable.
You can't just scale up your model.

As for quadrocopter piloting: right now, all pilots crash. Repeatedly.
Luckily, repairs are cheap (unless you happen to carry an expensive camera).
For a full-size aircraft, crashing is probably not an option, so add lots of
dev/testing time for safety features and pilot training.

BTW (somewhat unrelated): One huge problem with (smaller) quadrocopters is the
many people that start new copter projects and get nowhere instead of
contributing to one of the existing major projects or reusing its
soft/hardware. Some of these projects are already way beyond what a single
person or even a small team can achieve in a few years work.

~~~
eric-hu
Can you explain the physics behind why it's more efficient to have larger
rotors than multiple rotors?

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jackpirate
Two reasons. First, surface area. For an equivalent surface area, one rotor
results in a much smaller craft than 4 rotors.

Second, precision machining. It is much easier to balance 1 set of rotors
weighing hundreds of pounds than it would be to balance 4 of them. I'm
guessing your typical quadcopter is too small right now for this to be a real
concern.

~~~
Ao7bei3s
Balancing props is a very real concern, but for another reason than
efficiency: unbalanced props cause more vibration and lead to reduced
image/video quality due to the rolling shutter effect (image looks wobbly).
That being said, many people don't bother with propeller balancing.

Size of the aircraft is a very important point, but there are other reasons
besides the two you mentioned. Generally, larger _motors_ are more efficient
than smaller ones. Larger, slower, props are more efficient than smaller,
faster, ones, because Thrust ~ Rotor Speed^2 but Power ~ Rotor Speed ^ 3. Why?
I don't recall, sorry. I'm more interested in the software. (If you do figure
it out though, let me know.)

~~~
sopooneo
Because KE is proportional to v^2, and then you get another factor of v since
the volume (and thus mass) of air through the rotors per unit time is
proportional to how fast the air is moving.

At least that's my guess. And if I'm right, it's also why, to a first
approximation, the power generated by a windmill is proportional to the cube
of the wind speed.

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tunesmith
So, just get two larger quadrocopters and you could walk across a gorge. Each
one would just catch each of your steps.

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flavorcountry
I feel like it'd be insanely easier to, you know, ride one quadrocopter.
Across the gorge.

~~~
tunesmith
But, but.... um...

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jfoster
TED talk that preceded this, featuring 3 quadcopters with a net and ball:
<http://www.youtube.com/watch?v=C4IJXAVXgIo>

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tel
Could anyone put together a rough curriculum for the control theory needed to
understand something like this? It's absolutely fantastic.

~~~
femto
Read any "control theory"[1] text, frequently used in undergraduate
engineering courses. I hesitate to recommend the text from my undergraduate
years, as it wasn't very good, and is probably dated by now. The inverted
pendulum [2] is a canonical test in control engineering, frequently used to
test feedback control algorithms. Consequently, it should be treated in most
texts.

A separate problem is the modelling and control of the quadcopter. I say
separate, since the maths behind throwing an inverted pendulum should be
similar, whether it is being thrown by quadcopters or industrial robots. The
real (and more complex) story here is the quadcopter control algorithms. Using
an inverted pendulum is a sexy way to show off the quadcopted control
algorithms, compared to a dry graph of an error function.

[1] <https://en.wikipedia.org/wiki/Control_theory>

[2] <https://en.wikipedia.org/wiki/Inverted_pendulum>

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catilac
I feel like a link has popped up on HN, but I can't find it.

Where can I buy a small quadrocopter which I can program, and build my own
system with?

~~~
WA
I think you mean this one, right?

[http://www.seeedstudio.com/depot/preorder-crazyflie-nano-
qua...](http://www.seeedstudio.com/depot/preorder-crazyflie-nano-quadcopter-
kit-10dof-with-crazyradio-bccfk02a-p-1365.html?cPath=170_172)

~~~
catilac
Yes! Thank you. How did you search for that by the way?

~~~
femto
Translating your original question into a google search returns a relevant
result at position #2:

buy small quadcopter site:news.ycombinator.com

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hemancuso
Looking forward to when Amazon's warehouses are automated with quadrocopters.

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Wingman4l7
Kiva Systems already makes a warehouse robot. I didn't know if Amazon used
them or not, so I did some quick Googling and it turns out Amazon bought the
company! [http://dealbook.nytimes.com/2012/03/19/amazon-com-buys-
kiva-...](http://dealbook.nytimes.com/2012/03/19/amazon-com-buys-kiva-systems-
for-775-million/)

~~~
jayzee
and it was the same guy Raff D'Andrea who started that company

~~~
Wingman4l7
Hah, good catch! Small world =)

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Eliezer
Since this uses an explicit model of the world, Rodney-Brooks-style robotics
is now officially dead.

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mdda
I was puzzled by your comment. Is this Brooks paper[1] the thinking that
you're referring to?

[1] <http://people.csail.mit.edu/brooks/papers/representation.pdf>

~~~
Eliezer
Among others, but sure.

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mikekij
Holy crap, that's amazing. I'm excited when I can get MySQL started on my
development machine.

Those are some smart dudes ( and / or ladies).

~~~
rmollo
>dudes and ladies

You mean men and women. Although I didn't see any women in the video. (Better
include them just in case, so my friends don't think I'm a sexist pig!)

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speedyrev
All fun and games until they fly in your window at night and kill you in your
sleep.

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borplk
Imagine what kind of quadrocopters DARPA and similar agencies have these days.

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pointernil
"The Diamond Age: Or, a Young Lady's Illustrated Primer", Neal Stephenson

just saying ;) ...

~~~
pbhjpbhj
Why are you just saying that. Presumably that's a book suggestion, why is it
pertinent?

~~~
Simucal
"...then Bud made himself scarce, because the monitors - almond-sized
aerostats with eyes, ears, and radios - had probably picked up the sound of
the explosion and begun converging on the attack. He saw one hiss by him as he
rounded the corner, trailing a short whip antenna that caught the light like a
hairline crack in the atmosphere.

Aerostat meant anything that hung in the air. This was an easy trick to pull
off nowadays. Nanotech materials were stronger. Computers were infinitesimal.
Power supplies were much more potent...a device built with several thrusters
pointed along different axes could remain in one position or indeed navigate
through space." - The Diamond Age, by Neal Stephenson (1995)

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jordan_clark
Mathematics in motion is a beautiful thing.

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deadwait
how did they get arnold for the commentary?

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mauricio-OH
0.65s of pure robotics awesomness...

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sgoody
Batteries not included.

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davidradcliffe
Wow.

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evo_9
Congratulations - machines are one step closer to destroying the human race.

~~~
jeremyarussell
And only 999,999 more steps to go.

