Airflow on/around quadcopter drone

[mfb]

True, but with the center of mass below the plane of the rotors, stability would be greater than with the center of mass above the plane of the rotors.

I doubt that. It is not true for rockets, and quadrocopters are not that different from rockets in terms of passive stability.

 

[rcgldr]

True, but with the center of mass below the plane of the rotors, stability would be greater than with the center of mass above the plane of the rotors.

I doubt that. It is not true for rockets, and quadrocopters are not that different from rockets in terms of passive stability.

OK, my comment seems like the inverted pendulum fallacy for rockets. There are algorithms for quad rotors to balance inverted pendulums, ones that are bearing mounted. These rely on lateral movements to keep the inverted pendulum balanced. The same approach applies to a non-inverted pendulum, but the situation is more stable, since the pendulum would just swing back and forth even with no lateral correction by the quad rotor, and friction in bearing would dampen the oscillation.

With the pendulum directly connnected to the quad rotor, angular inertia is increased, and adverse torque could occur during lateral motion due to aerodynamic drag (due to the relative crosswind).

 

[mfb]

Torque needed to restore a vertical position is identical in both cases. The quadrocopter needs significantly more torque than usual, but again, that is common to both cases (above and below).
If you mount it as a pendulum which is free to rotate, things are different, but that's not the case here.

 

[rcgldr]

Torque needed to restore a vertical position is identical in both cases. The quadrocopter needs significantly more torque than usual, but again, that is common to both cases (above and below).

and more torque needed in order to lean for lateral movement. I updated my prior posts.

I was thinking more of the aerodynamic aspect and lateral stability in the case of a gusting crosswind or when trying to achieve and maintain lateral motion. In the case of a gusting crosswind, the inverted pendulum could cause the quad rotor to lean the "wrong" way (lean downwind), increasing the recovery time, while a non-inverted pendulum would cause the quad rotor to lean the "right" way (lean upwind, into the wind). In the case of lateral motion with a relative crosswind, the inverted pendulum could oppose the lean, while the non-inverted pendulum would increase the lean, some of which might be needed to overcome the lateral drag from the non-inverted pendulum.

I'm also wondering about any arrangement that would signficantly increase the angular momentum of a drone. Usually cameras are gimbal mounted, with separate gyro and servor drivers. When holding a camera orientation, the gimbal mount effectively acts as a bearing, reducing the impact of the camera and housing on the angular inertia perceived by the main part of the drone.

Getting back to the original post, and a later post with an article about showing a top mounted sensor on a quad rotor, this particular quad rotor uses relatively large rotors closely enough spaced that there may not be room to locate a sensor on top of the quad rotor.