Previously: https://news.ycombinator.com/item?id=48781539
Drone Physics
21–30 of 39 posts
Re: Drone Physics
#22I wrote something similar (though admittedly more in depth) some time ago: https://www.cggonzalez.com/blog/index.html
Re: Drone Physics
#23> This article describes drone physics. Audience should have familiarity with introductory linear algebra, introductory calculus, and introductory classical mechanics. Having familiarity with all 3, as soon as I read this sentence I knew it was all down hill for me.
Going down hill is easy, right?
Re: Drone Physics
#24> This article describes drone physics. Audience should have familiarity with introductory linear algebra, introductory calculus, and introductory classical mechanics. Having familiarity with all 3, as soon as I read this sentence I knew it was all down hill for me.
Going down hill is easy, right?
In general, no... most drones do not support negative altitude in their guidance systems.
The readers have a right to complain about LLM slop content. Especially when publishers use credential stuffing to sound authoritative with nonsense. =3
Re: Drone Physics
#25I was looking for an explanation of how you deal with the fact that quad rotors are under-actuated, and therefore you lack the complete control authority to do any arbitrary motion in space. So path planning has to take this into account, but how is this described?
Re: Drone Physics
#26Earlier quoted context omitted.
Why does four seem optimal? Why not three or five? or eight?
4, 6, and 8 are all fairly standard, as quadcopter, hexacopter, and octacopter, because you have a pair of motors rotating in each direction, which allows you to slow down all the motors spinning in one direction and speed up the others (as long as each set spinning the same direction is on opposite sides of the center of gravity), to maintain constant lift while yawing left or right. Tricopters are possible as tilt-…
> Two is possible if the payload hangs below the props
I think this is incorrect, it's the somewhat unintuitive rocket pendulum fallacy.
Re: Drone Physics
#27I was looking for an explanation of how you deal with the fact that quad rotors are under-actuated, and therefore you lack the complete control authority to do any arbitrary motion in space. So path planning has to take this into account, but how is this described?
Pitch and roll are coupled to fwd/back and Left/right respectively. So, you can make it move however you want, but its attitude can't be set independently of its motion. That's a simplification. One consequence is, for example, if you have a fixed camera mounted fwd etc, the angle it looks will correlate with the speed you have it move.
If you are just concerned with moving the center of mass to different locations in space, or have it travel with a specific velocity, you're fine.
This sort of limitation is common vehicles of all sorts; having 4 independent DOF is above average!
Re: Drone Physics
#28Earlier quoted context omitted.
4, 6, and 8 are all fairly standard, as quadcopter, hexacopter, and octacopter, because you have a pair of motors rotating in each direction, which allows you to slow down all the motors spinning in one direction and speed up the others (as long as each set spinning the same direction is on opposite sides of the center of gravity), to maintain constant lift while yawing left or right. Tricopters are possible as tilt-…
> Two is possible if the payload hangs below the props I think this is incorrect, it's the somewhat unintuitive rocket pendulum fallacy.
Here is a video of one: https://www.youtube.com/watch?v=qO747JB4Nr8
There's a few demonstrated here (26-32 seconds in): https://www.youtube.com/watch?v=vBsyFj8bEJk
And here's one that uses the ailerons instead of being able to tilt the motors: https://www.youtube.com/watch?v=L2fgL97rgK0
I could've sworn Peter Sripol built one while on Flite Test too, but I can't find it atm.
Looks like the rocket pendulum fallacy is about expecting meaningful passive stability from the location of the center of thrust vs center of mass, but even 2-rotors need to be able to tilt independently (or deflect thrust) for active control.
Theoretically this could still work even if the center of mass was above center of thrust, but the tilting/vectoring responsiveness would need to be very high. These RC models at least move so slowly that the air resistance of swinging back and fourth really does help dampen oscillations passively, but they all still have active flight controllers that are trying to keep angular velocity at zero without control input.
Re: Drone Physics
#29Earlier quoted context omitted.
4, 6, and 8 are all fairly standard, as quadcopter, hexacopter, and octacopter, because you have a pair of motors rotating in each direction, which allows you to slow down all the motors spinning in one direction and speed up the others (as long as each set spinning the same direction is on opposite sides of the center of gravity), to maintain constant lift while yawing left or right. Tricopters are possible as tilt-…
> Two is possible if the payload hangs below the props I think this is incorrect, it's the somewhat unintuitive rocket pendulum fallacy.
He specifically says if the motors independently tilt. This is active control. The Rocket pendulum fallacy is only valid for systems requiring passive stability.
Tandem rotor helicopters exist.
Re: Drone Physics
#30[dead]