5 ms·

Helicopters can autorotate under full engine failure. https://en.wikipedia.org/wiki/Autorotation https://en.wikipedia.org/wiki/Autorotation

TeMPOraL 9y ago
But can multirotors do that too? N-copters seem to have pretty small propellers; will they be able to store enough kinetic energy for autorotation? Also, AFAIK electric motors directly connected to propellers don't exactly have "idle" mode - they either use power or generate power.
- PhasmaFelis 9y ago
  For whatever it's worth, one of the other comments points out that heavy-lift drones are likely to be conventional helicopters rather than multicopters, since smaller rotors are less efficient.
- repiret 9y ago
  If the terminals of the motor are open, it will rotate freely.
- usrusr 9y ago
  Autorotation uses the energy stored in mass x height to spin the rotor for most of the descent, they are "charging" the kinetic storage until very close to the ground. This speed kinetic energy is only used for the final touchdown. The fixed pitch blades of a multicopter make this impossible. Autorotation is not a question of rotor mass, it's a question of pitch control. Lack of pitch control is the defining property of multicopters.
  - TeMPOraL 9y ago
    I forgot about pitch control, which is indeed the deciding factor here, but still - isn't the angular momentum used as that "kinetic energy storage"? Small, light propellers suck at that anyway.
    - jdmichal 9y ago
      We're talking about cargo drones, so I'm assuming the rotor would be relatively heavy duty compared to the size of the craft. And since we're talking unmanned, you can probably accept higher landing speeds than normal. You are really just interested in preventing a catastrophic landing, so navigating towards an empty area and not exploding on impact.
  - cr0sh 9y ago
    > Lack of pitch control is the defining property of multicopters. It is possible to do pitch-controlled propellers on a multi-copter. I recall that someone did this once for an engine-powered multi-rotor craft in order to be able to quickly vary the thrust from each rotor (using a servo that actuated the blade pitch via a rod that extended thru the rotor axle shaft) - because such engines usually can't be varied in speed/thrust as quickly as is needed for multi-rotor control.
    - baybal2 9y ago
      There certainly are Chinese makers of quads with pitch and collective for each rotor
    - usrusr 9y ago
      A lot is possible, even building a helicopter ;) While simple pitch control is certainly easier than the phase-dependent pitch control required for a helicopter, a pitch-controlled multicopter would lose a lot of the mechanics simplicity that made multicopters interesting in the first place. But autorotation control code for a pitch-multicopter would be an interesting challenge, maybe for the hobbyist who wants to dive deep doing more than just reimplementing stuff that already exists.

TeMPOraL 9y ago

But can multirotors do that too? N-copters seem to have pretty small propellers; will they be able to store enough kinetic energy for autorotation? Also, AFAIK electric motors directly connected to propellers don't exactly have "idle" mode - they either use power or generate power.

PhasmaFelis 9y ago
For whatever it's worth, one of the other comments points out that heavy-lift drones are likely to be conventional helicopters rather than multicopters, since smaller rotors are less efficient.
repiret 9y ago
If the terminals of the motor are open, it will rotate freely.
usrusr 9y ago
Autorotation uses the energy stored in mass x height to spin the rotor for most of the descent, they are "charging" the kinetic storage until very close to the ground. This speed kinetic energy is only used for the final touchdown. The fixed pitch blades of a multicopter make this impossible. Autorotation is not a question of rotor mass, it's a question of pitch control. Lack of pitch control is the defining property of multicopters.
- TeMPOraL 9y ago
  I forgot about pitch control, which is indeed the deciding factor here, but still - isn't the angular momentum used as that "kinetic energy storage"? Small, light propellers suck at that anyway.
  - jdmichal 9y ago
    We're talking about cargo drones, so I'm assuming the rotor would be relatively heavy duty compared to the size of the craft. And since we're talking unmanned, you can probably accept higher landing speeds than normal. You are really just interested in preventing a catastrophic landing, so navigating towards an empty area and not exploding on impact.
- cr0sh 9y ago
  > Lack of pitch control is the defining property of multicopters. It is possible to do pitch-controlled propellers on a multi-copter. I recall that someone did this once for an engine-powered multi-rotor craft in order to be able to quickly vary the thrust from each rotor (using a servo that actuated the blade pitch via a rod that extended thru the rotor axle shaft) - because such engines usually can't be varied in speed/thrust as quickly as is needed for multi-rotor control.
  - baybal2 9y ago
    There certainly are Chinese makers of quads with pitch and collective for each rotor
  - usrusr 9y ago
    A lot is possible, even building a helicopter ;) While simple pitch control is certainly easier than the phase-dependent pitch control required for a helicopter, a pitch-controlled multicopter would lose a lot of the mechanics simplicity that made multicopters interesting in the first place. But autorotation control code for a pitch-multicopter would be an interesting challenge, maybe for the hobbyist who wants to dive deep doing more than just reimplementing stuff that already exists.