
Every Quadrotor Needs This Failsafe Software - spectruman
http://spectrum.ieee.org/automaton/robotics/aerial-robots/every-quadrotor-needs-this-amazing-failsafe-software#.UxdDHIzx33Y.hackernews
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callmeed
I got my 3DRobotics IRIS a week ago. I've crashed it 3 times already,gone
through 4 replacement propellers, and busted my gimbal. None of my incidents
were due to a motor failing, I'm just a horrible pilot. Yesterday evening
while flying with the kids, we got too high and the wind drifted it down the
neighborhood. I switched it into "return to base" mode and it returned itself
into an avocado tree.

I guess what I'm saying is: this software looks really cool but I doubt it
will solve my current issues :)

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Florin_Andrei
Build yourself a foamie and fly that one until you learn RC piloting. Won't
help with the avocado tree, but it will surely help with the broken rotors.

[http://www.rcgroups.com/forums/showthread.php?t=1666155](http://www.rcgroups.com/forums/showthread.php?t=1666155)

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cube13
Or invest in a simulator package, and learn there.

It looks like Real Flight has quadcopters.

~~~
sean-duffy
Or buy a small quadcopter such as the Hubsan X4 for a fraction of the price,
and practise with that. :)

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akiselev
This is pretty cool. TLDR: in the case of failure, the quadcoptor starts to
tumble, just like a rocket reentering our atmosphere from a launch. Except
unlike with a rocket, the quadcoptor uses the remaining motors to keep itself
quasi-stable _while tumbling_. This keeps the quadcoptor rotating around the
path of descent and you can tweak the rotation through the last remaining
motors in order to change the over all flight path.

~~~
CamperBob2
This seems like an effect that would scale with the number of rotors. Makes me
wonder about the prospects of a craft with enough small rotors to approximate
a sphere.

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fasteddie31003
I hope the Arducopter community takes note of this algorithm and puts it in
future builds. Arducopter is in my opinion the best flight control board for
multicopters.

By the way I'm building a community to help RC builders show off their builds.
Take a look at some of the vehicles here
[http://www.rcbinder.com/vehicles](http://www.rcbinder.com/vehicles) . This is
my latest build [http://www.rcbinder.com/vehicles/aphid-
quad](http://www.rcbinder.com/vehicles/aphid-quad)

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pjc50
The article says "patent pending", so they'll have to come up with a different
one :(

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npsimons
As an aside, the IEEE is in favor of software patents, which is why I'm
currently boycotting them and not a member.

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btown
To be fair, the IEEE primarily represents researchers (in industry and
academia) who spend many years developing unique algorithms that, if any
software is deserving of a patent, would be the most deserving. I don't think
anyone's in favor of the existence of "swipe to unlock" type software patents.

~~~
dublinben
The owners of the "swipe to unlock" patent certainly are in favor of its
existence. Everyone always wants the law to specifically protect them, not
those other guys.

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lunixbochs
It was pretty lame when my quad caught a gust of wind, flipped upside down,
and cut off all motors to plummet ~150' onto a brick wall. Just had to replace
the crossbeam, but an ability to recover from extremely harsh conditions would
make me far more comfortable with flying it (higher than 15') anywhere but a
grass park.

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callesgg
How the fuck would it handle triple loss? 2 engine failures I can understand 3
not so much.

Also hope their patent fails. Physics should not be patentable.

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jfoutz
Imagine the thing tumbling. some % of the time, the remaining rotor will be
pointed in a useful direction, so you can give it the falling quad a push. If
you want it to fall slower, run the rotor when it's pointed vaguely up. If you
want it to fall somewhere safe (say to the north), run the rotor when it's
pointed vaguely north.

~~~
callesgg
I imagine that, that would mainly leed to the thing starting spinning more and
in the end make the crash even worse.

if they could fly a quad copter with only one rotor, the engineering behind
that is according yo me good enough to allow a patent.

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fancyketchup
(I can't watch the video) It certainly seems plausible that it _could_ work.

Imagine a copter with reversible motors that can respond quickly-enough
(weasel words!) to inputs from the control system. Now, the copter has angular
momentum along the direction perpendicular to the rotor disk and a vector
between the copter's center of mass and the working motor, and further that
the copter is oriented such that the vector is also parallel to the plane of
the ground.

As jfoutz said, running the motor ("forward") when the copter is upright and
off otherwise gives you net upward thrust (averaged over time). It also
applies a torque to the copter, which will _mostly_ be parallel to the extant
angular momentum vector. So, a first-order fix is to do what jfoutz said, but
also run the motor "backward" (negative thrust) when the copter is upside-
down. However, rotor also generates some torque perpendicular to the rotor
plane, which will cause the angular momentum vector to rise above the horizon
(since the motor reverses when it is upside-down, the angular momentum vector
rotates upward rather than revolving around the original direction of the
angular momentum vector).

However, if you allow the copter to have some angular momentum (i.e., you _don
't_ try to completely eliminate it), the rise might be slow enough to be
managed by running the motor at other times. For example, by running the motor
when the rotor plane is perpendicular to the ground, you could create a
similar drift in the angular momentum vector. But now it slowly drifts around
the compass instead of rising above the horizon. If you make the "compass"
drift faster than than the "altitude" drift, the torque from the first one
will average out to something very small. So by managing the rate of these two
drifts with an appropriate feedback loop, you can probably obtain a stable
solution where there is a net upward thrust and the angular momentum vector
"slowly" (for possibly large values of slow) precesses along the horizon.

~~~
callesgg
With reversible motor I see no problems it would take a shitload of a motor
but it could definitely work.

Unfortionaly the engines of the hobby quad copters we have today are not
reversible without a relay. And even if they where they would not be able to
change direction fast enough. One thing that could work is pitchble blades,
the problem with that is that it introduces a much bigger risk for failures.

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BrandonMarc
While we're on the topic of "every quadrotor should ____", how about the
improved efficiency of this design?

[http://spectrum.ieee.org/automaton/robotics/aerial-
robots/ir...](http://spectrum.ieee.org/automaton/robotics/aerial-
robots/iros-2013-should-quadrotors-all-look-like-this)

See also:

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

... and, if you have IEEE privileges, the paper is here:

[http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6...](http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6696530)

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deletes
Would it be possible to mount a miniature deployable parachute on such
quadcopters, and keep the fly time mostly intact?

~~~
pjc50
What do you mean by "keep the fly time mostly intact"?

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deletes
It doesn't weight much relative to copter, so battery charge is not affected.

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chrisfarms
Should this technique technically work for the failure of two motors too
(assuming the remaining motors are opposite)? Or would it be impossible to
build up the inertia for a stable spin? If motors could rotate, could it even
fly on one? ... so many questions, maybe I should just build one.

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kcorbitt
I'm no control theory expert, but I have a hard time imagining how you could
control a quadcopter in 3+ degrees of freedom with only a single input (the
speed of your single remaining motor) no matter how fancy your algorithms get.

However, as unwind mentions, the researchers in the article claim it's
possible.

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ChuckMcM
The essence of the algorithm is that you spin in the horizontal plane. If you
have enough power your single remaining motor can create a vertical airstream
that will keep the altitude constant. The limit on spinning is the structural
integrity of the system with all that angular momentum, the limit on flying is
the frequency response of your control system.

A number of people have built and demonstrated so called 'half prop'
helicopters based on the same principle. If you have ever seen an maple seed
fall you can understand the principle, search for 'maple copter' on Youtube
for some videos of them in action.

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kenrikm
Example: [http://www.livescience.com/12725-maple-copter-robotic-
craft-...](http://www.livescience.com/12725-maple-copter-robotic-craft-mimics-
falling-maple-seed.html)

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jeffrogers
Or just fly a Y-6 configuration instead of a quad and you can afford to loose
a prop/motor... no additional software/algos needed.

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vutekst
Very true, but with the caveat that you have now increased your motor, prop,
and ESC budget by 50%. And of course this will impact your battery life, as
coaxial arrangements trade away some efficiency for this redundancy.

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lsaferite
Then just make it a hex copter and do away with the coaxial arrangement. You
still have 6 motors, 3 per rotation direction. With good software you could
still fly with the loss of one motor per rotation direction with practically
no control degradation. You could lose 2 on a single rotation direction and
still likely control it enough to land.

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benihana
Looks like I triple E is taking a play out of the Upworthy Headline Writing
Playbook.

~~~
DoggettCK
#{your_town} mom discovers one wierd trick to safely land quadcopter. The FAA
hates her!

