I was looking for the previous discussion on this topic and could not find it, but to recap my contribution to it;

Multi-copters became possible when several technologies got light enough and cheap enough.

The first was perhaps 6 and later 9 degrees of freedom MEMS (silicon) sensors (gyro, acceleration, magnetics). Early helicopter models required too much work to fly, but these sensors combined with cpus made multicopters 'fly by wire'

The second was a rechargable and light battery chemistry (Lithium Polymer batteries) which allow a multicopter to fly for a useful amount of time.

The third was brushless motor controllers which allowed for the creation of high power, but light, motors that were also efficient.

Some will also add high power SoCs (embedded 32 bit computers of 'cell phone class') but early multicopters were powered by 8bit controllers so I'm not sure that this is as important as the other three.

The things that are common to all of them, lightness and energy efficiency, these made the multicopter possible and as the price has been driven down with mass production for these parts it has made them easy to obtain for a big enough market. (and that is a positive feedback loop, the market grows, the quantity increases, the price goes down, the market grows ...)

The MEMS sensors, high power SoCs and sophisticated battery chemistry in a light/cheap form were all (arguably) enabled by the mass production of smartphones.

Now that multicopters are beginning to ramp up the mass adoption curve and drive innovations of their own will we see this same kind of technological cross pollination happen to other fields with what's being created for multis?

The pace of innovation in brushless speed controllers has been exciting to watch, but I can't think of what other applications there are for brushless motors that accelerate quicker or can change direction nearly instantly. Lots of work seems to be happening in the position tracking arena, with everything from cameras to sonar arrays to lidar being considered and used both professionally and on the hobbyist scene.

I really want to see one of Googles project tango boxes used as a sensor to do real time object avoidance on a quad.

Adressing object avoidance. Intel and AscTec are ahead in the game ;) [1]. But I agree that this indeed will become more and more prominent and really interesting in the coming years!

"[...] Someday obstacle avoidance technology in UAVs will be like seatbelts in cars: You simply don’t start going without it!” [2]

- Daniel Gurdan, CEO Ascending Technologies GmbH.

[1] https://www.youtube.com/watch?v=Us0BqJvsF9k

[2] http://www.asctec.de/en/ascending-technologies-and-intel-col...

There were drivers for each of the technologies that were independent of the combination of them as a smart phone. And they were singular, which is to say each technology, by itself, was important to some ecosystem. I used a mems gyro for example in an R/C car in the late 90s to tell me it was upside down and switch the left/right steering.

Around 2002 two german guys set the path for today's quadcopters. They built the X-UFO and developed the X-3D and X-3D-BL sensors [1], which for the first time enabled amazing control capabilities for the still rather unknown quadcopters [2]. This led to the first success stories and the market kind of jumped on the train. Media did it's job and here we are. Technology has advanced a lot since then [3, 4]. Better and smaller sensors and microprocessors. More sophisticated materials and design, production and marketing processes. This surely played a big role as well, now that consumer market UAVs and flying toys can be produced quite cheaply. Also various open source projects popped up and nowadays even beginners can build and program their own quadcopter and PID controller.

As for helicopter vs. quadcopter - The latter is much simpler to fly, especially with autopilots and control units such as the X-3D or today's AscTec Trinity. Also safety for consumer products is an issue, where quadcopters with their embedded propellers have the bonus. And its omni-directional nature of movement yields more freedom and fun, especially as a toy.

[1] http://www.asctec.de/en/ascending-technologies/company/

[2] https://www.youtube.com/watch?v=Csti6mHZNF4

[3] https://www.youtube.com/watch?v=Us0BqJvsF9k

[4] see ChuckMcM's comment

One of the AsTec founders (Daniel Gurdan) has an interesting back story.

Playing with explosives in his basement he lost part of his hand. Being an avid juggler he was sad that he could not juggle clubs anymore.

He built himself an robotic hand which won the first price at the German youth science competition [1]. He was 16 at the time.

The quadcopter was his follow up project and a main component of that project was that the copter was controlled with a glove[2].

Referenced articles are in German, but the images are worth a click.

[1] http://www.jugend-forscht.de/projektdatenbank/jonglierhandsc...

[2] http://www.jugend-forscht.de/projektdatenbank/die-ufos-komme...

Have you ever flown a (toy) helicopter? They are very non-intuitive. The torque of the main rotor causes every course change to have side effects that have to be compensated for.

Change the engine speed (lift), and the tail rotor needs to be adjusted so the copter does not yaw.

Change the tilt of the rotor blades to lean fore/after or drift to the side, and the engine needs to be sped up just a little to avoid slight loss of lift, and the tail rotor needs an ajustment to avoid yaw for the increased torque.

With multiple lifting, fixed, rotors, the electronics adjust the motor speeds for you to DWIM when you manipulate the sticks.

My friend with a helicopter license felt cheated the first time he flew a plane and discovered how easy it was.

I once took a helicopter lesson, and I watched some videos about flying before hand.

One of the guys said: "A plane wants to fly. A helicopter wants to crash". This seems true to me: flying a helicopter is a continual act of not crashing.

It makes complete sense to me that a quadcopter is 100x easier to write software to autonomously fly vs a helicopter design.

There's a popular quote in the pilot community:

"The thing is, helicopters are different from planes. An airplane by it's nature wants to fly, and if not interfered with too strongly by unusual events or by a deliberately incompetent pilot, it will fly. A helicopter does not want to fly. It is maintained in the air by a variety of forces and controls working in opposition to each other, and if there is any disturbance in this delicate balance the helicopter stops flying; immediately and disastrously. There is no such thing as a gliding helicopter.

This is why being a helicopter pilot is so different from being an airplane pilot, and why in generality, airplane pilots are open, clear-eyed, buoyant extroverts and helicopter pilots are brooding introspective anticipators of trouble. They know if something bad has not happened it is about to."

Harry Reasoner, Approach magazine, November 1973

The pedant in me feels obligated to point out that helicopters can accomplish unpowered landings using autorotation.

If I had to make a choice about which unpowered craft to be in though-- I'll take the plane!

Is there any data on this? Let's assume both an airplane and helicopter with highly trained and skilled pilots, with both aircraft high enough and going fast that there is time for the pilots to have time to fully prepare and react when they suddenly lose power.

It is certainly not obvious to a non-pilot like me that the plane is safer. If the plane can reach an airport, then sure. The plane pilot has less work to fly the plane then the auto rotating helicopter pilot has, so presumably can better concentrate on the landing. As long as he puts it down with enough room to stop, he should be fine.

But if they are not in range of an airport, so it is going to be a landing in a park or on a highway or something like that, would the plane still be safer? From the various videos I've seen of landings under such conditions, it seems that the big killer for planes is that they land with a lot of forward velocity. Essentially an unpowered plane landing outside an airport becomes a rough touchdown followed by effectively a high speed car crash in a car that was not really designed for that kind of crash.

The helicopter, on the other hand, wouldn't have much horizontal velocity, and so it would just be a rough landing.

Autorotation requires action from a skilled pilot, it doesn't happen automatically. It's also one-shot maneuver - if you fail it, you're done, and you can't abort it like you could abort an unpowered plane landing.

How do you abort an unpowered plane landing?

You basically answered it yourself upthread - the plane has lots of forward velocity on approach, which gives the pilot a pretty big window to abort by gliding away, turning some of this forward velocity into lift.

I fly RC planes, or on a good day, gliders. Much more relaxing.

If I can get an indoor toy heli to hop from one kitchen counter to the other, I feel like I've accomplished something. They are slippery beasts. I don't even want to think about flying a heli outside in wind.

We watched a real heli rescue some hikers/climbers in the park outside Las Vegas on a windy day a few years ago on vacation. The wind was blowing against the cliff. Dicey stuff.

Robert Mason's book on being a Huey pilot in Vietnam, 'Chickenhawk'does a great job of explaining traditional helo dynamics. Great book.

http://en.wikipedia.org/wiki/Chickenhawk_%28book%29

Also, with a multicopter you have N identical motors. Turning, moving and tilting is still complicated, but easier enough for the electronics of today

But why there's no trend of multicopters replacing helicopters? Big ones, with humans inside.

Multiple small rotors is much less efficient than one big rotor, especially at bigger scale. So it's not economical.

I've been into the hobby (building, flying and racing multicopters) for about 10 months now-- I personally think it was a combination of factors with the biggest one being the advent of the tiny / cheap gyro and accel sensors mostly used in smartphones. The catalyzing event for the hobbyist side of things was the release of the Nintendo Wii-- since the wiimote controllers were a readily available and relatively cheap source of these components the hobbyist "scene" really converged around an open source project to hack together active flight controllers from wii controllers and arduino boards. These flight controllers are what allows multicopters to hover so effortlessly-- the computer does all the hard work of balancing motor speeds on the millisecond timescale. (If you could go back and give one of these boards to the guys at NASA in the 60's they would have called it cheating.)

Obviously I've painted that with a very broad brush and people with different opinions will show up to tell me about how I'm wrong and a noob-- but this is how I see the history in a nutshell. Traditional model RC electric airplane components were also getting better and cheaper in conjunction with the birth of $20 flight computers. Faster and more efficient motors running on smaller better speed controllers, all powered by lithium polymer batteries that not only have great energy density and discharge capability but have become almost a commodity product thanks to modern consumer electronics.

MEMS sensor (gyros/accelerometers) technology developed for smartphones made cheap multicopter control systems possible.

I think small and mid-sized quads have dropped in price / increased in quality because of the fall in the price for gyroscopes, accelerometers, and ICs that can do decent sensor fusion. If you have ever broken these parts, you know that quadcopters are effectively impossible to fly. As for the preference over helicopters, multicopters all have fixed pitch rotors, which are cheaper.

I think they also benefit from increased mindshare given UAVs in the news.

I can't speak to why it wasn't invented sooner, but I do think that the biggest reason that they've taken off (pun?) is that they are much easier to fly and much more stable than a helicopter. The fact that many of them now have cameras attached to them that offer professional-quality photos and videos, along with the ability to get a live feed while in-flight, is definitely making them more and more popular every day.

I'd agree with the ability to get images and post them is a huge draw.

But I just spent a few minutes reading some about quadcopters vs even helicopters and from what I have read everyone so far seems in agreement that the quadcopters are less stable and less efficient then a helicopter design. It is the software stabilization that makes flight even possible, but even then they aren't very stable.

I had always wondered about this, as I have seen model helicopters (and full sized) maintain a level hover for significant time periods, but I can't ever recall a nearly still level hover from a quadcopter. From reading it sounds like that is tough to achieve given that they are constantly adjusting power to each of 4 motors to maintain flight and without the ability to change pitch of the blades that is the only option. So while mechanically easier to build they aren't necessarily more stable.

>but I can't ever recall a nearly still level hover from a quadcopter.

Seriously? Every one of the DJI products can do this out of the box using just GPS/accel/gyro/barometer. Newer ones can do it even better by adding in a camera pointing at the ground that works like an optical mouse. Some really insane stuff can be done if you throw an active positioning system into the mix: http://www.ted.com/talks/raffaello_d_andrea_the_astounding_a...

Just saw that, thanks for the link. I stand corrected, I hadn't personally seen them stay very still in a hover before, maybe it was operator inexperience.

If the quad has only an accel and gyro sensor onboard then yes, the stability will be based primarily on the skill of the pilot and how well the machine is tuned.

With a GPS and barometer thrown in, position hold should be pretty close to a still hover unless there is significant wind or unresolved problems with the power train

I'm surprised that GPS has enough accuracy to do a position hold. Why, then, my cellphone GPS is accurate only to 5-10 meters?

The copter doesn't need to know where it is, just whether it is moving and if so, how far and in what direction. Because the error in GPS measurements doesn't vary much in small time frames, that can be done more accurately than absolute position measurements. See http://en.m.wikipedia.org/wiki/Differential_GPS.

A "good" GPS system (the DJI version is ~$100 by itself I think) should be able to get you down to just a few inches of precision, but yes, the market is flooded with cheap (~$20) units that aren't nearly as useful for position hold (hovering completely still) but can still give you a good lat/long and do well with navigation, distance measuring or acting as a reference sensor for a automatic direction tracking antenna. Cell phones are similarly hit or miss-- some have nicer GPS modules than others, but ultimately the user is unlikely to notice this since smartphone style road navigation only requires 10 meters or so of accuracy and a vague single position can be greatly refined in that context by knowing the road/map layout as well as the direction and speed of travel.

That makes sense. Thanks for sharing more info, I like learning.

I've bought various helicopters through the years as gifts but they always get totalled on their 2-3 flight. The quadcopters I bought are still in good nick, are cheap to replace parts for and are very intuitive. The entry level models are £30 and robust enough for beginners.

level hover without stick input, will fly back to position if moved: [1]

[1] https://www.youtube.com/watch?v=OsATmfRC0U4

That is awesome. How is the "home" position set? Is it from where it starts or do you preprogram it? Also, how is elevation determined? GPS or an on board sensor?

Home is usually set where you power up / take off at, however there are plenty of users who can report that their misconfigured home position ended up with a drone taking off at full speed towards Shenzen or the 0,0 lat/long point off Africa.

Elevation can be determined by GPS, but a barometer works better.

Cool, that makes sense, thank you again.

I would think a barometer would work far better. GPS is not the best for vertical accuracy.

There are pros and cons to both-- PCB mount baros don't always respond well in settings with lots of moving air and various other nearby components that get warm-to-hot during operation.

Keep in mind for either method you also have an accelerometer, so even if GPS (or a crummy baro) provides a messy signal for altitude you can average it over a given timespan and compare that against how quickly you are accelerating upwards or downwards.

Yes, I think the ability to get instant high-quality pictures back and put them on the internet is the big sell that's new.

From an aerodynamic efficiency and maneuverability standpoint, a traditional single rotor helicopter is far superior. However, the operational benefits, safety, and mechanical simplicity (way less expensive when they crash) of the multirotor configuration make it a very popular choice. The confluence of better battery technology and cheap/lightweight controllers has allowed for increased viabiliity. As the commercial drone industry matures and payload carrying missions become viable, I expect there to be a shift in popularity back to the single rotor configuration. For example, more than 30% of Japan's rice paddy fields are sprayed with Yamaha's single rotor drone [http://textually.org/drones/2013/06/032493.htm]. There is an exception here; the multirotor configuration is a more stable platform for shooting video.

Being able to do this: [1] https://www.youtube.com/watch?v=NsxyV-kgfio

Using these: [2] http://www.fatshark.com/product/1757.html

Is also a contributing factor to the popularity ;-)

You can watch this happen in real time too-- every once and a while a video like this will bubble up through social media, hitting the reddit frontpage and making the rounds on facebook. Then TC or pando will run an article featuring the video and suddenly all the domestic part shops are out of stock for a week!

I think cheap rare earth magnets was a factor, although I suspect only a part of the reason. The motors are now far smaller, lighter and more powerful, as well as cheap to produce. Given you need four of them, they are now light enough that a small (therefore also cheap) battery can give a useful range to them, so you can have a very effective device at mass-market prices.

Controller boards and multi-axis sensors became cheap, powerful, and easy to work with. Companies then sprang up with pre-made kits that weren't too expensive.

If you're interested in seeing the start of this craze, check out the Wii Copter. The sensors in the Wii controllers, and also cheap boards like the Arduino, made it so any hobbyist could build one.

Pun intended?

Anyways, a university experiment video that went viral [0] is the first I recall seeing a quadcopter in action. Maybe the tipping point if you care to investigate further.

[0]: https://www.youtube.com/watch?v=YQIMGV5vtd4

Yep, same here. May have seen another article or video that same year but that was the one that stuck in my head. Kind of sad that I didn't even get a "toy" quad until this year but I ought to be building my own sometime this summer.

I feel old. This video is a late addition to the quadcopter world. But then again, while multicopters were popular within DIY scene for some time, they only recently went mainstream and started being sold to "normals".

I was going to reference the software that makes it possible for complete amateurs to fly these things, but there's no reason that the software couldn't have been developed 30 years ago. So the answer is probably battery technology (driven by cell phones).

Lithium-polymer batteries are much better than the old Nickel-Cadmium batteries we had when I was a kid. Also, brushless motors (with electronic controllers) are much more efficient than brushed motors. The power to weight ratio of electric propulsion in the last 10 years is incredible.

The software wasn't the hard part. The hard part was getting a multi million dollar military airplane gimbal sensor precise enough to fly by into a package that could both fit on a circuit board and be cheap enough to mass produce.

Smartphones got us that.

Simplicity and cost. At its most basic form a quadcopter is just two sticks, 4 motors with four speed controllers a flight controller and a battery. [1] if crashed they are easily repaired. a single rotor helicopter on the other had is more mechanically complex, more fragile and more expensive to repair. The reason they became popular was that different technologies (battery, ESCs, flight controllers) all aligned and some very good work was put into open source software to control them lowering the barrier to entry.

[1] http://undcon.com/rc/quadcopter/img_20101002_011858.jpg

Legal observation:

The tip of a single blade helicopter has much more energy than the tip of a roughly 1/4 radius of a quad-copter blade.

Despite the complexity, if the copter is large, I would think there's much less liability baked into a quad-copter.

Reality backs this up, a stunt pilot more or less decapitated himself with a heli a while back and while I've seen plenty of rough multicopter injuries ranging from bruises to lacerations I'm not aware of anyone who has managed to kill themselves with one... yet.

The two new biggest upcoming industries (VR and Drones) seem to have their origins with smartphones. Cheap screens and cheap/accurate gyros. Which all 3 got their start from cheap/fast computing.

I think its mostly the fact that technology caught up and became cheap enough. Battery technology, motor technology (brushless), electronics (ESC's which control the motors, and the onboard boards with gyros and accelerometers) and many other things.

I'd attribute it the most to battery technology. As part of the hobby myself, Ni-Cad batteries were the go-to's. But they were crappy. Li-Pos have existed before, but the thing about multi-rotors and flying in general is it doesn't need a high capacity, but a high output rate, which we can get now.

The reason that you see so many multicopters for the smaller ones is that they are much mechanically simpler, and thus cheaper to manufacture. All you need mechanically for a multicopter is a number of independent rotors that you can vary the speed on.

A traditional helicopter has a very complicated assembly to allow powering a rotor that can tilt forward, backwards, and to the sides, as well as change the angle of the blades. This is a lot more expensive to produce.

It is more efficient, in a power to weight ratio sense, to have only a single motor, which is why you see this design on full-sized helicopters. But for smaller, cheaper drones, you don't need as good of a power to weight ratio to make it worthwhile, and the cheaper simpler design makes them easier to mass-produce and sell to amateurs or professionals on a budget.

The things that probably have led to an explosion of them recently include electronics getting cheaper, and control systems getting better. Regular helicopters can be piloted by a skilled operator with some training. A mutlicopter needs a automated control system to keep it balanced. As electronics for the control systems have gotten cheaper, as well as MEMS sensors (accelerometers and gyroscopes built into ICs), these control systems have become cheap and easy to integrate into mass produced products.

In addition, battery technology has been improving, as has electric motor technology. While previously only the single big fossil fuel engine was the only viable power source, as battery capacity has increased and electric motors have gotten more efficient, it's more viable to have small electric copters.

Another thing that makes these more accessible to casual amateurs, and again makes mass production more viable, is that most people now carry around a flexible input device with wireless control capabilities. That means that you can sell devices without a dedicated controller, can do things like streaming video back from the drone, and so on, increasing the range of things that you can do with one.

Other technological improvements also help feed into this. Having widely available, small, light HD and 4K cameras means that you can actually do something useful with these drones; back when to do any real filming you needed a big, bulky camera, they weren't as efficient for getting aerial shots, but once there are small, light, high quality cameras, it becomes feasible.

The quadcopter design is much simpler and cheaper but less stable (before electronic stabilization) and efficient than a helicopter. The popularity is probably due to a combination of easy handling (with modern gyros/electronics), robustness, low cost and the trend to film everything. Helicopters are difficult to control and more suited to serious applications (carrying weight, long flight times...).

I really don't know, but a quick search popped up this article.

http://www.forbes.com/sites/quora/2013/12/23/what-makes-the-...

Those who are interested edx is featuring a course on quadcopter https://www.edx.org/course/autonomous-navigation-flying-robo...

My understanding is that the quad rotor configuration is more stable at low reynolds numbers, but I'm not a rotary wing expert.

This sounds rather far-fetched to me.

Original presentation in 2012: https://www.youtube.com/watch?v=jl5v3bsMH_E

Past events:

Oct 5, 2012 - Berlin by Core Team & JSConf.eu

Oct 20, 2012 - Dublin by Paul Campbell

Oct 31, 2012 - San Francisco by Christian Sanz

Nov 8-9, 2012 - Seattle, WA by Chris Williams

Nov 10, 2012 - Brighton by Remy Sharp

Dec 1, 2012 - San Francisco by Christian Sanz & Jyri Engeström

Jan 23, 2013 - Zurich by Jordi Boggiano

Mar 2, 2013 - Oslo by Trygve Lie & Gregers Gram Rygg

Mar 16, 2013 - London by Andrew Nesbitt

Mar 23, 2013 - Bath by Andrew Nesbitt

Apr 20, 2013 - Helsinki by Janne Aukia and Team

May 11, 2013 - Scotland by Andrew Nesbitt & Julian Cheal & Scotland.js

May 30, 2013 - Amelia Island by Core Team & JSConf.us

Jul 27, 2013 - Manchester by Andrew Nesbitt

Aug 10, 2013 - Southampton by Andrew Nesbitt & Julian Cheal

Aug 18, 2013 - London by Andrew Nesbitt

Sep 7, 2013 - Cincinnati by Jim Weirich & Carin Meier

Sep 13, 2013 - Berlin by Core Team

Sep 21, 2013 - Bristol by Andrew Nesbitt

Sep 28, 2013 - Berlin by Henri Bergius (NoFlo Edition!)

Oct 4, 2013 - Lisbon by A few Portuguese guys

Oct 13, 2013 - New York City by Core Team

Nov 23, 2013 - Sheffield by Julian Cheal & Caolan McMahon

Dec 6-7, 2013 - Amelia Island by Chris & Laura (RobotsConf!)

Jan 23, 2014 - Istanbul by Kod Mutfağı

Feb 12, 2014 - London by Andrew Nesbitt

Mar 17, 2014 - Warsaw, Poland by Core Team & Makerland

May 29, 2014 - JSConf, Florida by Core Team & JSConf

(and there's a year of other events since then - they need to update the website)

See http://www.nodecopter.com/