6 ms·

Why haven't quadcopters been scaled up yet?

111 points by vitoc 12y ago

jamesaguilar 12y ago
Distilled: - Large rotors are more efficient than small rotors. - Because of the square-cube law, bigger, heavier aircraft require higher fuel energy densities than can be delivered by batteries. Therefore you need a relatively complex engine rather than simple motors, and you can't afford to replicate it four times. - A variety of handling and safety benefits of helicopters compared to quad rotors.
- randallsquared 12y ago
  As someone down the page mentions, hybrids seem like the obvious solution to this set of problems.
- ObviousScience 12y ago
  Trains require a HUGE engine, yet they relay their power via electrical linkage. This is actually more efficient than other systems, because it allows the engine to run at its optimum power generation cycle, without worrying about converting RPM down to the appropriate amount via mechanical linkage. An electrical linkage would be relatively straightforward to split in to 4 components.
  - bdonlan 12y ago
    It's still a lot of weight to carry around a high-power generator, large-gauge power cables (or heavy transformers and smaller-gauge cables), and four electric motors. This is less of a problem on a train, because the train only has to deal with the additional friction, and doesn't have to worry about generating more lift to make up for the increased weight.
  - dredmorbius 12y ago
    Being able to individually step wheels is also a big win -- if a given wheel starts to lose traction, it's much easier to cut electrical power than mechanical. Steel-wheel-on-steel-rail has fairly low static friction (which is why you find electrically-powered trains with many powered wheelsets, and virtually _all_ trains with track-sanding capabilities to increase traction).
- IshKebab 12y ago
  Most people are still missing the real reason, which is that quadrocopters vary thrust by changing the speed of the rotors. You can only do that with small rotors due to inertia, so with large rotors you'll need variable pitch to change the thrust. And if you have variable pitch you only need one rotor. The only exception to this is to have many small fixed pitch propellers, which has been done and is probably quite attractive from a price point of view, and to a certain extent safety (although you can't autogyro). But it is undoubtedly less efficient.
jonah 12y ago
What I'd like to see are more small "drones" with alternate arrangements. Counterrotating Coaxial for example.[1] http://www.youtube.com/watch?v=DUGEjQdoylY http://www.youtube.com/watch?v=DUGEjQdoylY
- miahi 12y ago
  As many of the other answers say, the current multicopters are very simple, mechanically: an electric motor directly coupled to a fixed-pitch propeller. Everything is controlled by the amount of current the motors receive. Any other alternate arrangement means a more complex mechanical control: servos, gears, larger propellers, variable-pitch propellers... This makes them less reliable, harder to mend and more dangerous (that's one of the reason model helicopters never really caught on, even with modern electronic stabilizers - even a smaller 450-class blade can break bones if you hit it).
SoftwareMaven 12y ago
This is the interesting answer there, IMO. An interesting take on a real multi-prop vehicle: https://www.advancedtacticsinc.com https://www.advancedtacticsinc.com The video linked at the bottom is worth a watch.
kashkhan 12y ago
They are coming... http://zee.aero/ http://zee.aero/ http://www.jobyaviation.com/S2/ http://www.jobyaviation.com/S2/ For practical reasons and redundancy more than four rotors is better.
- spacefight 12y ago
  Zee: Zero learned. A better insight can be gained here: http://www.gizmag.com/flying-car-zee-aero/29890/ http://www.gizmag.com/flying-car-zee-aero/29890/ S2: Interesting concept - the battery density will still be an issue.
  - kashkhan 12y ago
    yep. there are pictures floating of the zee aero plane. http://cdn.slashgear.com/wp-content/uploads/2013/11/6r363-on-Instagram-611x420.png http://cdn.slashgear.com/wp-content/uploads/2013/11/6r363-on... If your mission is 100miles radius electric is doable. 200kg payload, 200kg airframe and 200kg batteries (100kWh) 6minute hover at 200kW => 20kWh 30minute flight at 200mph (60kW) => 30kWh 1/2 hour margin for legal reasons. low hover tip speed (200m/s) for low noise.
Crito 12y ago
> "The only effect that can make quadcopter stable is having centre of gravity below centre of lift just like normal helicopter." This strikes me as incorrect (http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy), though I am not totally confident of that.
- baddox 12y ago
  It sounds wrong to me as well. I would think you would want the center of lift as close as possible to the center of gravity, and that you would also want the flight controllers accelerometers and gyroscopes in the same spot.
  - deleted 12y ago
    [deleted]
utopkara 12y ago
It must be the costs... Multirotors have enjoyed open source development by enthusiasts so far, and they built heavily on the experience of the RC enthusiasts, and they repurposed tons of hardware that is suitable for small applications. A few thousand dollars is within the budget of many developers, so the small UAV improvements could proceed very much like software-based innovation curve does. But, any size/budget/project bigger than that is bound by a different progress curve. I bet it can be done, and if it is practical, it will be done too. Aerospace engineers were always a very innovative bunch; check out autogyro (https://en.wikipedia.org/wiki/Autogyro https://en.wikipedia.org/wiki/Autogyro).
- waps 12y ago
  It's not the cost. The problem is electrical planes. Helicopters are known for their agility, coming at the cost of extreme energy use (and, imho, extreme danger. Any mechanical failure in any part of the helicopter WILL result in contact with the ground in 2 minutes or less. Redundancy (in your standard helicopter craft) is effectively zero). Getting a normal plane to fly electrical is a huge challenge. Getting a helicopter to fly electrical is a bigger challenge. In 2011, for the first time in history, a manned helicopter took flight. More than 1/4th of the flight mass was batteries and that afforded the craft ~2 minutes of powered flight (hover, not maneuvering). [1] We just don't have the electrical storage solution to pull it off easily. It's not impossible at these efficiencies either, but it's bloody hard. It's not just electrical power that falls short. For the longest time, planes were quite picky fuel wise and gasoline also fell short. Even today, it's not gasoline that's used, even though most planes will fly fine on your car's gasoline (not diesel though), even corn ethanol, but less efficient (range reduction of ~20-30%). The answer to most of the "can we do X with electricity" is simply : find a way to store 4 times (or more) the electrical power in something the size and weight of our best batteries (take lithium-polymer), and it'll work. Without that, it's barely possible. We do have things that store electrical power more effectively than a battery, but you won't like them. Plutonium batteries would easily allow for an electrical helicopter and would allow it to remain flying constantly for 40 years straight (or more if you like, thousands of years wouldn't be out of the question, really). There are a few other nuclear options that would provide similar performance. But I don't think I need to explain why this isn't done. Plutonium batteries have the advantage that they do direct electricity generation, making them very, very small and efficient. Also, in space, temperature is supposedly -271 degrees celcius, but because there's no gas colliding with the craft, heat will take weeks to leak away from the spacecraft. So anything with a heat based generator (which is nearly everything) is out. Which is why plutonium batteries are pretty much the only answer. [1] http://www.industrytap.com/worlds-first-electric-powered-helicopter/3693 http://www.industrytap.com/worlds-first-electric-powered-hel...
ghostdiver 12y ago
Does it necessarily has to be a *copter? http://en.wikipedia.org/wiki/Hawker_Siddeley_Harrier http://en.wikipedia.org/wiki/Hawker_Siddeley_Harrier
- Sami_Lehtinen 12y ago
  There's a long list of VTOL aircrafts, but all of those are more or less horrible compromises. https://en.wikipedia.org/wiki/List_of_VTOL_aircraft https://en.wikipedia.org/wiki/List_of_VTOL_aircraft
moepstar 12y ago
While it is a multi-copter instead of a quad, this thing looks promising: http://www.e-volo.com/ http://www.e-volo.com/ Video of first flight is on this page: http://www.e-volo.com/ongoing-developement/vc-200 http://www.e-volo.com/ongoing-developement/vc-200
milankragujevic 12y ago
A quadcopter changes direction by spinning up or down the appropriate set of propellers. The smaller the propellers, the less energy (time) it takes to slow them down. Meaning a huge quadcopter is increadibly unstable and can't change direction fast enough for anything. They're uselessly inefficient other than the smallest ones (flying circuit board, ~4cm long) and the bigger ones just use bigger batteries and have the same flight time (mainly for lifting cameras, but they too are slower or use much more energy to go the same speed as the small ones).
- exDM69 12y ago
  > A quadcopter changes direction by spinning up or down the appropriate set of propellers. To extend on this further... a quadcopter uses the motors to quickly change the speed of the blades rotating. This requires a lot of power, depending on the inertia of the rotor. The inertia of the rotor is roughly proportional to the fifth power of the blade length. Double the blade length, 32x the inertia. The power requirements of this forbids scaling up. Contrast this with a traditional helicopter, where the rotor is spinning at stable speed (low engine torque requirement) and the helicopter is controlled by changing the pitch of the blades. The pitch of the blades changes during every rotation and is controlled with a mechanism called a "swashplate". There have been "hybrid" helicopter designs involving a variable pitch propeller in a quadcopter as well as supplementing a quad with a large propeller for lift. But the most promising research on quadcopters is focusing on using several independent quadcopters co-operatively.
  - milankragujevic 12y ago
    That's what I meant. I'm bad at talking, I mainly just play with quadcopters and "study" their flight. IMO, I like them as they're really cheap, much cheaper than fixed pitch or collective pitch single rotor nano helicopters, and coaxials are really slow to respond and are incredibly bad at handling even minor wind.
  - Gravityloss 12y ago
    You can have collective pitch setting in a quadcopter, with which you can scale up quite a lot without having to go to full cyclic pitch control (helicopters). So basically it's a spectrum of scale: 1) fixed pitch (small quads) 2) collective pitch (large quads, autogyros) 3) cyclic and collective pitch (real helicopters)
jokoon 12y ago
Also electrical rotors have much finer control than a piston engine.
- jacquesm 12y ago
  Electrical fixed rotors. Once you have a swashplate to give you variable pitch that can be used to give you the same kind of control that you get by changing the RPM and the electrical advantage disappears.
Arcanum-XIII 12y ago
There's alternative to the common arrangement of a motor per blade, like the http://curtisyoungblood.com/V2/products/quadcopters/stingray-500 http://curtisyoungblood.com/V2/products/quadcopters/stingray... - one motor, variable pitch. It's clearly more complex, but you gain agility, motor efficiency and it seem to give a better running time.
WalterBright 12y ago
An airplane is a vehicle that wants to fly, a helicopter wants to crash. A helicopter is inherently unstable and requires constant adjustment. It has multiple single points of failure, any one of which will result inevitably in a crash. This is dealt with by insanely expensive quality control, constant inspections, and constant maintenance. The quadcopter doesn't improve on this, it makes it worse. It has 4 engines - if one engine fails, it crashes. It has inherently 1/4 of the reliability of a single engine helicopter. Losing one rotor blade will also cause a crash, so its 1/4 of the reliability there as well. QA, maintenance, and overhauls will cost 4x as much.
- serf 12y ago
  http://spectrum.ieee.org/automaton/robotics/aerial-robots/every-quadrotor-needs-this-amazing-failsafe-software http://spectrum.ieee.org/automaton/robotics/aerial-robots/ev... stable flight is not impossible with the loss of a motor on a quadrotor platform. it's currently stuck in labs, but the dynamics are doable.
  - miahi 12y ago
    That kind of stable flight is ok for an unmanned vehicle, but I don't think a passenger/pilot would be delighted abut that kind of accelerations and spin.
    - louthy 12y ago
      I guess if it's a choice between smashing into the ground and short period of spinning whilst an automated system landed the vehicle, I think I know what I'd go for.
      - ljf 12y ago
        Depending on how fast you are spinning, I imagine the deceleration on landing, for a human passenger would be lethal or life threatening.
    - gvr 12y ago
Terr_ 12y ago
The same reason the birds and the bees have radically different wings. Scaling up insect flight to bird size does not go well, because physical properties do not scale evenly.
- keenerd 12y ago
  Scaled up insects work just fine when the atmosphere has 50% extra oxygen. Birds figuratively ate them for lunch, but for several million years 70cm wingspans were not uncommon for dragonflies.
ck2 12y ago
Can quadcopters safely land on three motors? How about less?
- Istof 12y ago
  http://diydrones.com/profiles/blogs/new-algorithm-can-save-a-quadcopter-after-one-motor-prop-failure http://diydrones.com/profiles/blogs/new-algorithm-can-save-a...
Htsthbjig 12y ago
Because quadcopters are naturally unstable, so you need complex electronics(and sensors and electric motors) to control it. You can make helicopters very stable just with weights in the rotor, like any RC fan knows. Until very recently the inertial motion control complex elements were very expensive. Accelerometers in cars and gyros in smartphones later had made those sensors inexpensive. The iPhone was released in 2007, that was 7 years ago. Every air device carries gyros inside, but for controlling the plane they had to give you a digital signal, it is not enough with the artificial horizon sphere. The simple helicopter design has been mass produced for decades(and wars like Vietnam subsidized them more), and it is well tested and reliable. Any new design has to compete in price and will have to iron lots of bugs at first. The second most important reason is that you need to use electric motors as normal heat engines could not respond as fast as needed. So in order to make a quadcopter you need to generate electricity onboard, which means a big hybrid engine. I see quadcopters as the future, but in order to compete in price, they will have to evolve from small UAVs.
- Htsthbjig 12y ago
  PS: In order to understand how much wars influenced the development of helicopters, my father used to work manufacturing helicopters in Spain. When Vietnam war ended, the market become so saturated and the prices went down so much that the company my father worked in could not compete and closed its doors.
- headShrinker 12y ago
  You touch on a number of good points here. It's true you need accelorometers measuring and giving feedback a few hundred times a second. Electric motors are the only motors that can respond to feedback that fast. So the batteries will be a big deal on a scaled up quad. The most important aspect you didn't mention is that they are inherently inefficient. The more blades you have, the more inefficiency is introduced. that's why scaling them up doesn't make much sense.
  - mrestko 12y ago
    Why couldn't you use a turbine to generate electricity that is then fed to electric motors controlling the blades? Is there actually a requirement for large, efficient batteries?
Sami_Lehtinen 12y ago
Here's one quadcopter design which is more efficient that most of older designs: http://www.geek.com/science/weve-been-designing-quadcopters-incorrectly-since-day-one-1577256/ http://www.geek.com/science/weve-been-designing-quadcopters-...
dharma1 12y ago
Also wondering if VTOL multi rotor/fixed wing hybrids could be scaled up
- dharma1 12y ago
  Appears they can http://www.janes.com/article/42425/darpa-awards-boeing-contract-for-phantom-swift-as-new-vtol-x-plane http://www.janes.com/article/42425/darpa-awards-boeing-contr...
tim333 12y ago
The Lady Gaga copter is quite funky http://www.10news.com/news/lady-gaga-takes-flight-in-hovering-dress-designed-in-part-by-carlsbad-pilot-11242013 http://www.10news.com/news/lady-gaga-takes-flight-in-hoverin...
lotsofcows 12y ago
One major reason for multi rotor machines is to avoid the classic helicopter problem of the rotor blade's leading edge approaching the speed of sound while the trailing blade is simultaneously stalling. Unfortunately, this would require such a scaling up of existing quadcopter designs that it's unlikely to ever happen for all the reasons already listed.

111 points by vitoc 12y ago

Distilled: - Large rotors are more efficient than small rotors. - Because of the square-cube law, bigger, heavier aircraft require higher fuel energy densities than can be delivered by batteries. Therefore you need a relatively complex engine rather than simple motors, and you can't afford to replicate it four times. - A variety of handling and safety benefits of helicopters compared to quad rotors.

randallsquared 12y ago
As someone down the page mentions, hybrids seem like the obvious solution to this set of problems.
ObviousScience 12y ago
Trains require a HUGE engine, yet they relay their power via electrical linkage. This is actually more efficient than other systems, because it allows the engine to run at its optimum power generation cycle, without worrying about converting RPM down to the appropriate amount via mechanical linkage. An electrical linkage would be relatively straightforward to split in to 4 components.
- bdonlan 12y ago
  It's still a lot of weight to carry around a high-power generator, large-gauge power cables (or heavy transformers and smaller-gauge cables), and four electric motors. This is less of a problem on a train, because the train only has to deal with the additional friction, and doesn't have to worry about generating more lift to make up for the increased weight.
- dredmorbius 12y ago
  Being able to individually step wheels is also a big win -- if a given wheel starts to lose traction, it's much easier to cut electrical power than mechanical. Steel-wheel-on-steel-rail has fairly low static friction (which is why you find electrically-powered trains with many powered wheelsets, and virtually _all_ trains with track-sanding capabilities to increase traction).
IshKebab 12y ago
Most people are still missing the real reason, which is that quadrocopters vary thrust by changing the speed of the rotors. You can only do that with small rotors due to inertia, so with large rotors you'll need variable pitch to change the thrust. And if you have variable pitch you only need one rotor. The only exception to this is to have many small fixed pitch propellers, which has been done and is probably quite attractive from a price point of view, and to a certain extent safety (although you can't autogyro). But it is undoubtedly less efficient.

jonah 12y ago

What I'd like to see are more small "drones" with alternate arrangements. Counterrotating Coaxial for example.[1] http://www.youtube.com/watch?v=DUGEjQdoylY http://www.youtube.com/watch?v=DUGEjQdoylY

miahi 12y ago
As many of the other answers say, the current multicopters are very simple, mechanically: an electric motor directly coupled to a fixed-pitch propeller. Everything is controlled by the amount of current the motors receive. Any other alternate arrangement means a more complex mechanical control: servos, gears, larger propellers, variable-pitch propellers... This makes them less reliable, harder to mend and more dangerous (that's one of the reason model helicopters never really caught on, even with modern electronic stabilizers - even a smaller 450-class blade can break bones if you hit it).

SoftwareMaven 12y ago

This is the interesting answer there, IMO. An interesting take on a real multi-prop vehicle: https://www.advancedtacticsinc.com https://www.advancedtacticsinc.com The video linked at the bottom is worth a watch.

kashkhan 12y ago

They are coming... http://zee.aero/ http://zee.aero/ http://www.jobyaviation.com/S2/ http://www.jobyaviation.com/S2/ For practical reasons and redundancy more than four rotors is better.

spacefight 12y ago
Zee: Zero learned. A better insight can be gained here: http://www.gizmag.com/flying-car-zee-aero/29890/ http://www.gizmag.com/flying-car-zee-aero/29890/ S2: Interesting concept - the battery density will still be an issue.
- kashkhan 12y ago
  yep. there are pictures floating of the zee aero plane. http://cdn.slashgear.com/wp-content/uploads/2013/11/6r363-on-Instagram-611x420.png http://cdn.slashgear.com/wp-content/uploads/2013/11/6r363-on... If your mission is 100miles radius electric is doable. 200kg payload, 200kg airframe and 200kg batteries (100kWh) 6minute hover at 200kW => 20kWh 30minute flight at 200mph (60kW) => 30kWh 1/2 hour margin for legal reasons. low hover tip speed (200m/s) for low noise.

Crito 12y ago

> "The only effect that can make quadcopter stable is having centre of gravity below centre of lift just like normal helicopter." This strikes me as incorrect (http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy), though I am not totally confident of that.

baddox 12y ago
It sounds wrong to me as well. I would think you would want the center of lift as close as possible to the center of gravity, and that you would also want the flight controllers accelerometers and gyroscopes in the same spot.
- deleted 12y ago
  [deleted]

utopkara 12y ago

It must be the costs... Multirotors have enjoyed open source development by enthusiasts so far, and they built heavily on the experience of the RC enthusiasts, and they repurposed tons of hardware that is suitable for small applications. A few thousand dollars is within the budget of many developers, so the small UAV improvements could proceed very much like software-based innovation curve does. But, any size/budget/project bigger than that is bound by a different progress curve. I bet it can be done, and if it is practical, it will be done too. Aerospace engineers were always a very innovative bunch; check out autogyro (https://en.wikipedia.org/wiki/Autogyro https://en.wikipedia.org/wiki/Autogyro).

waps 12y ago
It's not the cost. The problem is electrical planes. Helicopters are known for their agility, coming at the cost of extreme energy use (and, imho, extreme danger. Any mechanical failure in any part of the helicopter WILL result in contact with the ground in 2 minutes or less. Redundancy (in your standard helicopter craft) is effectively zero). Getting a normal plane to fly electrical is a huge challenge. Getting a helicopter to fly electrical is a bigger challenge. In 2011, for the first time in history, a manned helicopter took flight. More than 1/4th of the flight mass was batteries and that afforded the craft ~2 minutes of powered flight (hover, not maneuvering). [1] We just don't have the electrical storage solution to pull it off easily. It's not impossible at these efficiencies either, but it's bloody hard. It's not just electrical power that falls short. For the longest time, planes were quite picky fuel wise and gasoline also fell short. Even today, it's not gasoline that's used, even though most planes will fly fine on your car's gasoline (not diesel though), even corn ethanol, but less efficient (range reduction of ~20-30%). The answer to most of the "can we do X with electricity" is simply : find a way to store 4 times (or more) the electrical power in something the size and weight of our best batteries (take lithium-polymer), and it'll work. Without that, it's barely possible. We do have things that store electrical power more effectively than a battery, but you won't like them. Plutonium batteries would easily allow for an electrical helicopter and would allow it to remain flying constantly for 40 years straight (or more if you like, thousands of years wouldn't be out of the question, really). There are a few other nuclear options that would provide similar performance. But I don't think I need to explain why this isn't done. Plutonium batteries have the advantage that they do direct electricity generation, making them very, very small and efficient. Also, in space, temperature is supposedly -271 degrees celcius, but because there's no gas colliding with the craft, heat will take weeks to leak away from the spacecraft. So anything with a heat based generator (which is nearly everything) is out. Which is why plutonium batteries are pretty much the only answer. [1] http://www.industrytap.com/worlds-first-electric-powered-helicopter/3693 http://www.industrytap.com/worlds-first-electric-powered-hel...

ghostdiver 12y ago

Does it necessarily has to be a *copter? http://en.wikipedia.org/wiki/Hawker_Siddeley_Harrier http://en.wikipedia.org/wiki/Hawker_Siddeley_Harrier

Sami_Lehtinen 12y ago
There's a long list of VTOL aircrafts, but all of those are more or less horrible compromises. https://en.wikipedia.org/wiki/List_of_VTOL_aircraft https://en.wikipedia.org/wiki/List_of_VTOL_aircraft

moepstar 12y ago

While it is a multi-copter instead of a quad, this thing looks promising: http://www.e-volo.com/ http://www.e-volo.com/ Video of first flight is on this page: http://www.e-volo.com/ongoing-developement/vc-200 http://www.e-volo.com/ongoing-developement/vc-200

milankragujevic 12y ago

A quadcopter changes direction by spinning up or down the appropriate set of propellers. The smaller the propellers, the less energy (time) it takes to slow them down. Meaning a huge quadcopter is increadibly unstable and can't change direction fast enough for anything. They're uselessly inefficient other than the smallest ones (flying circuit board, ~4cm long) and the bigger ones just use bigger batteries and have the same flight time (mainly for lifting cameras, but they too are slower or use much more energy to go the same speed as the small ones).

exDM69 12y ago
> A quadcopter changes direction by spinning up or down the appropriate set of propellers. To extend on this further... a quadcopter uses the motors to quickly change the speed of the blades rotating. This requires a lot of power, depending on the inertia of the rotor. The inertia of the rotor is roughly proportional to the fifth power of the blade length. Double the blade length, 32x the inertia. The power requirements of this forbids scaling up. Contrast this with a traditional helicopter, where the rotor is spinning at stable speed (low engine torque requirement) and the helicopter is controlled by changing the pitch of the blades. The pitch of the blades changes during every rotation and is controlled with a mechanism called a "swashplate". There have been "hybrid" helicopter designs involving a variable pitch propeller in a quadcopter as well as supplementing a quad with a large propeller for lift. But the most promising research on quadcopters is focusing on using several independent quadcopters co-operatively.
- milankragujevic 12y ago
  That's what I meant. I'm bad at talking, I mainly just play with quadcopters and "study" their flight. IMO, I like them as they're really cheap, much cheaper than fixed pitch or collective pitch single rotor nano helicopters, and coaxials are really slow to respond and are incredibly bad at handling even minor wind.
- Gravityloss 12y ago
  You can have collective pitch setting in a quadcopter, with which you can scale up quite a lot without having to go to full cyclic pitch control (helicopters). So basically it's a spectrum of scale: 1) fixed pitch (small quads) 2) collective pitch (large quads, autogyros) 3) cyclic and collective pitch (real helicopters)

jokoon 12y ago

Also electrical rotors have much finer control than a piston engine.

jacquesm 12y ago
Electrical fixed rotors. Once you have a swashplate to give you variable pitch that can be used to give you the same kind of control that you get by changing the RPM and the electrical advantage disappears.

Arcanum-XIII 12y ago

There's alternative to the common arrangement of a motor per blade, like the http://curtisyoungblood.com/V2/products/quadcopters/stingray-500 http://curtisyoungblood.com/V2/products/quadcopters/stingray... - one motor, variable pitch. It's clearly more complex, but you gain agility, motor efficiency and it seem to give a better running time.

WalterBright 12y ago

An airplane is a vehicle that wants to fly, a helicopter wants to crash. A helicopter is inherently unstable and requires constant adjustment. It has multiple single points of failure, any one of which will result inevitably in a crash. This is dealt with by insanely expensive quality control, constant inspections, and constant maintenance. The quadcopter doesn't improve on this, it makes it worse. It has 4 engines - if one engine fails, it crashes. It has inherently 1/4 of the reliability of a single engine helicopter. Losing one rotor blade will also cause a crash, so its 1/4 of the reliability there as well. QA, maintenance, and overhauls will cost 4x as much.

serf 12y ago
http://spectrum.ieee.org/automaton/robotics/aerial-robots/every-quadrotor-needs-this-amazing-failsafe-software http://spectrum.ieee.org/automaton/robotics/aerial-robots/ev... stable flight is not impossible with the loss of a motor on a quadrotor platform. it's currently stuck in labs, but the dynamics are doable.
- miahi 12y ago
  That kind of stable flight is ok for an unmanned vehicle, but I don't think a passenger/pilot would be delighted abut that kind of accelerations and spin.
  - louthy 12y ago
    I guess if it's a choice between smashing into the ground and short period of spinning whilst an automated system landed the vehicle, I think I know what I'd go for.
    - ljf 12y ago
      Depending on how fast you are spinning, I imagine the deceleration on landing, for a human passenger would be lethal or life threatening.
  - gvr 12y ago

Terr_ 12y ago

The same reason the birds and the bees have radically different wings. Scaling up insect flight to bird size does not go well, because physical properties do not scale evenly.

keenerd 12y ago
Scaled up insects work just fine when the atmosphere has 50% extra oxygen. Birds figuratively ate them for lunch, but for several million years 70cm wingspans were not uncommon for dragonflies.

ck2 12y ago

Can quadcopters safely land on three motors? How about less?

Istof 12y ago
http://diydrones.com/profiles/blogs/new-algorithm-can-save-a-quadcopter-after-one-motor-prop-failure http://diydrones.com/profiles/blogs/new-algorithm-can-save-a...

Htsthbjig 12y ago

Because quadcopters are naturally unstable, so you need complex electronics(and sensors and electric motors) to control it. You can make helicopters very stable just with weights in the rotor, like any RC fan knows. Until very recently the inertial motion control complex elements were very expensive. Accelerometers in cars and gyros in smartphones later had made those sensors inexpensive. The iPhone was released in 2007, that was 7 years ago. Every air device carries gyros inside, but for controlling the plane they had to give you a digital signal, it is not enough with the artificial horizon sphere. The simple helicopter design has been mass produced for decades(and wars like Vietnam subsidized them more), and it is well tested and reliable. Any new design has to compete in price and will have to iron lots of bugs at first. The second most important reason is that you need to use electric motors as normal heat engines could not respond as fast as needed. So in order to make a quadcopter you need to generate electricity onboard, which means a big hybrid engine. I see quadcopters as the future, but in order to compete in price, they will have to evolve from small UAVs.

Htsthbjig 12y ago
PS: In order to understand how much wars influenced the development of helicopters, my father used to work manufacturing helicopters in Spain. When Vietnam war ended, the market become so saturated and the prices went down so much that the company my father worked in could not compete and closed its doors.
headShrinker 12y ago
You touch on a number of good points here. It's true you need accelorometers measuring and giving feedback a few hundred times a second. Electric motors are the only motors that can respond to feedback that fast. So the batteries will be a big deal on a scaled up quad. The most important aspect you didn't mention is that they are inherently inefficient. The more blades you have, the more inefficiency is introduced. that's why scaling them up doesn't make much sense.
- mrestko 12y ago
  Why couldn't you use a turbine to generate electricity that is then fed to electric motors controlling the blades? Is there actually a requirement for large, efficient batteries?

Sami_Lehtinen 12y ago

Here's one quadcopter design which is more efficient that most of older designs: http://www.geek.com/science/weve-been-designing-quadcopters-incorrectly-since-day-one-1577256/ http://www.geek.com/science/weve-been-designing-quadcopters-...

dharma1 12y ago

Also wondering if VTOL multi rotor/fixed wing hybrids could be scaled up

dharma1 12y ago
Appears they can http://www.janes.com/article/42425/darpa-awards-boeing-contract-for-phantom-swift-as-new-vtol-x-plane http://www.janes.com/article/42425/darpa-awards-boeing-contr...

tim333 12y ago

The Lady Gaga copter is quite funky http://www.10news.com/news/lady-gaga-takes-flight-in-hovering-dress-designed-in-part-by-carlsbad-pilot-11242013 http://www.10news.com/news/lady-gaga-takes-flight-in-hoverin...

lotsofcows 12y ago

One major reason for multi rotor machines is to avoid the classic helicopter problem of the rotor blade's leading edge approaching the speed of sound while the trailing blade is simultaneously stalling. Unfortunately, this would require such a scaling up of existing quadcopter designs that it's unlikely to ever happen for all the reasons already listed.