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Comment by jawns | Hacker News Reader

I keep trying to think of practical implications for this technology, but every time I do, I just end up daydreaming about robot circuses.

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Balancing an inverted pendulum is one of the classic "hard" problems in control theory. (At least, in undergrad.) Not only has he solved that on a flying platform, but he's going to the next levels.

Tossing sticks around between flying robots isn't inherently useful, but it means they have a foundation for further, more complex work.

well you can do a single inverted pendulum pretty easily with a PID controller, it's the double inverted pendulum that is hard. But anything on a quadrocopter is really hard.

A free-flying small quadcopter is incredibly difficult as on-board sensors generally consist of noisy, drift-prone MEMS gyros and accelerometers, small and interference-sensitive magnetometers, bad civilian GPS, and barometers that are prone to environmental fluctuation. In addition, a free-flying quadcopter requires either complete autonomy or an RF link with some range or reliability, which generally requires a good amount of power.

But these aren't free-flying quadcopters; the researchers used a very high-end motion capture rig and a PC in close proximity, making everything a lot less difficult - with motion capture, positional accuracy is quite easy and sensor noise is easy to correct for, and with enough money someone else has already solved the latency issues in motion-capture for you.

I certainly agree this video is impressive but I also believe lab-only motion capture-based demos skew the hobbyist and public vision of what small quadcopters can do.

Did you see the show from Cannes last year?

http://www.youtube.com/watch?v=cseTX_rW3uM&t=50

I don't know how much of that was motion-capture, it seems like a quite difficult environment to have done that...

Read the video description: "Thanks to Vicon for the tracking system" - the same system used in this juggling video, as far as I know.

I think all of the KMel Robotics projects (at least all of the ones I've seen on video, like the Bond theme) have used the same basic design, which involves a Vicon system.

I wonder how they get it to work in a dark room with some _very_ bright moving lights? IR with really good visible light filters maybe?

I think so. Like most motion-capture systems, Vicon systems use high-frequency strobe lights to illuminate markers being tracked. IR strobing is definitely an option for these systems. I, too, am quite impressed that they worked in that situation, as the range on IR strobes is usually much worse than NIR and especially red ones. I suppose with the way the lighting is set up the cameras could have been in relatively close proximity behind the stage.

All the issues you mentioned ring a bell. Is there any progress in the hobbyist area on developing inline smoothing filters and adaptive kalman filters to clean the signals and compensate for drifts using all the instrumentation readings available?

I think Paparazzi probably have the most interesting adaptive control algorithms and sensor fusion code, although their community is perhaps smaller than other open-source flight control solutions: http://paparazzi.enac.fr/wiki/Main_Page . I guess they're not strictly hobbyist since as a university project, various contributors also publish several papers a year.

Pretty much everyone in the open-source arena (Ardupilot, OpenPilot, Paparazzi, PARIS/WiiCopter) experiments with various filtering approaches and sensor fusion strategies.

One interesting challenge is that more sensors increases cost and hobbyists are often cash-strapped (especially after crashing a lot!), so sensor fusion isn't as heavily pursued as adaptive control and basic filtering strategies for 6-axis input.

Ah, thanks for that.

I had a lot to do with the question of "where the hell are we & how the hell do we get to where we should be" in real time and to fairly tight tolerances (at scale) - sadly/luckily at the time it was left to the pilot to follow the blinking light rather than deal with the mechanics of moving control surfaces directly.

The main thrust of surveys like [1] though was enhanced final product accuracy through sensor fusion strategies, using calibration flights to tune filters to remove induced magnetic field effects from aircraft headings, using lidar, microwave, accelerometers, differential ground GPS, temperature, pressure, and humidity to get good estimates for actual height clearances, estimates for the mass of air column, etc, etc, blah, blah, old guy stuff.

That's a single survey of many, performed over decades, and it was interesting in the evolution of processing to watch it move from post processing to in line processing. Which of course prompted the question.

The paparazzi (seriously france? this is for drone RC craft to snap pics of celebrity boobs?) project pages look interesting, so I'll dive into those.

[1] Fiji, 1997 "A combination of helicopter and fixed wing aircraft was used to fly the survey with a total of 160, 000 line kilometers of data acquistion (~80,000km per aircraft type)"

http://webcache.googleusercontent.com/search?q=cache:http://...

Occasionally, quadcopters surprise people and seemingly inexplicably do hard things without trying:

http://diydrones.com/profiles/blogs/why-doesnt-the-ball-fall...

You can only control a inverted pendulum using a PID if it's near one of its equilibrium points. You need a linearized model of the dynamics and this is usually done using the small angle aproximation for the sine. I don't think they are using a PID controller for the pendulum in that video.

Oh, you're right. I was thinking of the double inverted pendulum.

actually you can control a single inverted pendulum with an on/off controller that is fast enough...

Indeed, the inverted pendulum is a textbook exercise. This is how cranes work: you don't want the heavy thing at the end of the cable to swing. This is how helicopter-cranes work too, but with added wind. They almost look as if they were nailed to the sky: the only trick is to have fast sensors, which are a given for literally decades now.

The only change is that sensors are manufactured in such large quantities, that they are so cheap that they are omnipresent (ie. almost every phone -- inconceivable decades ago). Quadcopters are also more stable by design than one would think (easier to stabilize than conventional ones).

I'd like to see an aerial battle-bots event. Imagine a giant transparent cube or orb 'stadium', with entry points for opposing fleets. There might be capture-the-flag or last-man-standing victory conditions, and a variety of units, perhaps including dirigibles.

> There might be capture-the-flag

How about "Transport the flag?" Or how about a bunch of flags? The other team is allowed to try and disrupt your transportation as well.

I want them to throw some sort a water-balloon like device at each other and have them try to gently catch it. Except this balloon explodes with fire instead of water if it can't catch it softly.

Capture the flag generally implies "transport the flag."

I was going for something like the economy in StarCraft. You have a stream of poles shot into the arena from catapults, and scoring is based on how many get transported back to each team's goal. (Minus the exponential increase, though.)

I can't read this and not think Quidditch-minus-Snitch.

Quadditch! Man, forget the Robocup (http://www.robocup.org/), I would watch the hell out of a Quadditch tournament.

You could use a little copter as the snitch.

In the eternal words of HPMOR!Harry,

"And then whichever Seeker gets lucky swoops in and grabs the Snitch and makes everyone else's work moot. It's like someone took a real game and grafted on this pointless extra position so that you could be the Most Important Player without needing to really get involved or learn the rest of it. Who was the first Seeker, the King's idiot son who wanted to play Quidditch but couldn't understand the rules?"

I entirely agree that the seeker less variant is a more interesting participant sport. The seeker variant will probably be requested since it is canon, at least at first.

On the other hand, "keeping your eyes moving in a pattern" sounds like a thing that would be interesting for computer vision.

Or "build the biggest tower"?

Build and defend!

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

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

That's where the juggling algorithm comes into play.

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

Or simply stronger windows.

Or a person can use a grenade launcher

Simple. Have the drone hold on to them for long enough that they explode before the others have a chance to return it.

From PBS's Rise of the drones http://www.pbs.org/wgbh/nova/military/rise-of-the-drones.htm...

They profiled a new type of drone which is basically a human-controlled missile. Fly it right into a window!

I'm actually a bit curious why we haven't yet seen any reports of organized crime related hits using cheap drones and explosives.

I'd just make the drones the bomb. Instead of the bomb deploy-er. These things will only get cheaper to produce anyway.

Yep, that's the way it will evolve, I think. Let's say you can mass-produce a drone with anti-tank explosive for $5000. That's much cheaper than guided anti-tank missiles we have now. And they can be designed to only work for 10 minutes, so no good quality materials required.

Make 1000 of them ($5 000 000 is sth like 1 tank), put them in groups of 20 in 50 places where you suspect enemy will attack. Program them to wait with sensors on, when they detect enemy tanks they go up, land on tanks and explode. Tanks usually have much less armor on the top.

Little ones with a small amount of thermite could fly into the gun barrels of main battle tanks.

Presumably the drone is the "grenade" and so performs evasive tactics. Targetted EMP? Or simply has a "balloon" to make it physically unable to exit the window again (bonus that the balloon blocks out natural light inside and seals the explosion magnifying the effect inside, eg for flashbang).

Smart grenades?

It's sad that research like this is first thought to be most of value killing people.

How is that sad? If it's not useful for sex, what else is more important than killing people?

Feeding people.

http://tacocopter.com/

They are going nuts over this. Just look at DARPA drone research, all the manufacturing contracts, the increased battlefield use, the call for more pilots to be trained...

Lots of scary things are possible as the hardware gets smaller/lighter/stronger and the control algorithms get more sophisticated.

Grenade lobbing is quite pedestrian compared to "precision targeting" in the video here: http://bit.ly/W6DnuO

They are already doing this: http://www.dailymail.co.uk/news/article-2281403/U-S-Air-Forc...

That's practical enough for me.

You could catch someone falling off a building or airplane with a (suitably large and fast) quadrocopter, I suppose.

Waiter, another beer please.

Please tilt head upward and open mouth.

I heard that you can weaponize unmanned aerial vehicles ...

My first thought was "I want to see these juggle three poles". Nothing wrong with robot circuses.

Construction comes to mind immediately, but yeah, I'm a sucker for those videos.

http://www.youtube.com/watch?v=SNPJMk2fgJU Aiming bullets, not poles.

Building emergency shelters as quickly as possible?

Repairing wind-blown greenhouses in remote places as quickly as possible?

Building a water-pipe as quickly as possible?

Elevator-to-the-stars building mechanic?

lol. I can only come up with gaming applications. flying robots that build stuff(jenga?), air battles.

I recently got a vacuum roomba and I am very entertained just on by watching it work. But I am a geek, probably not everybody is like that.

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