3 ms·

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 the

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)
Retric 12y ago
You could change the pitch on the blades a lot faster than you can change their rotation speed. But, at that point a helicopter becomes not just more efficient and stable, but easier to build as well.

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)

Retric 12y ago

You could change the pitch on the blades a lot faster than you can change their rotation speed. But, at that point a helicopter becomes not just more efficient and stable, but easier to build as well.